File: rfc8705.html

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<!DOCTYPE html>
<html lang="en" class="RFC">
<head>
<meta charset="utf-8">
<meta content="Common,Latin" name="scripts">
<meta content="initial-scale=1.0" name="viewport">
<title>RFC 8705: OAuth 2.0 Mutual-TLS Client Authentication and Certificate-Bound Access Tokens</title>
<meta content="Brian Campbell" name="author">
<meta content="John Bradley" name="author">
<meta content="Nat Sakimura" name="author">
<meta content="Torsten Lodderstedt" name="author">
<meta content="
       
  This document describes OAuth client authentication and certificate-bound
  access and refresh tokens using mutual Transport Layer Security (TLS)
  authentication with X.509 certificates.  OAuth clients are provided a
  mechanism for authentication to the authorization server using mutual TLS,
  based on either self-signed certificates or public key infrastructure (PKI).
  OAuth authorization servers are provided a mechanism for binding access
  tokens to a client's mutual-TLS certificate, and OAuth protected resources
  are provided a method for ensuring that such an access token presented to it
  was issued to the client presenting the token.
 
    " name="description">
<meta content="xml2rfc 2.40.1" name="generator">
<meta content="JSON Web Token" name="keyword">
<meta content="JWT" name="keyword">
<meta content="MTLS" name="keyword">
<meta content="Mutual TLS" name="keyword">
<meta content="proof-of-possession" name="keyword">
<meta content="proof-of-possession access token" name="keyword">
<meta content="key confirmed access token" name="keyword">
<meta content="certificate-bound access token" name="keyword">
<meta content="client certificate" name="keyword">
<meta content="X.509 Client Certificate Authentication" name="keyword">
<meta content="key confirmation" name="keyword">
<meta content="confirmation method" name="keyword">
<meta content="holder-of-key" name="keyword">
<meta content="OAuth" name="keyword">
<meta content="8705" name="rfc.number">
<link href="rfc8705.xml" rel="alternate" type="application/rfc+xml">
<link href="#copyright" rel="license">
<style type="text/css">/*

  NOTE: Changes at the bottom of this file overrides some earlier settings.

  Once the style has stabilized and has been adopted as an official RFC style,
  this can be consolidated so that style settings occur only in one place, but
  for now the contents of this file consists first of the initial CSS work as
  provided to the RFC Formatter (xml2rfc) work, followed by itemized and
  commented changes found necssary during the development of the v3
  formatters.

*/

/* fonts */
@import url('https://fonts.googleapis.com/css?family=Noto+Sans'); /* Sans-serif */
@import url('https://fonts.googleapis.com/css?family=Noto+Serif'); /* Serif (print) */
@import url('https://fonts.googleapis.com/css?family=Roboto+Mono'); /* Monospace */

@viewport {
  zoom: 1.0;
  width: extend-to-zoom;
}
@-ms-viewport {
  width: extend-to-zoom;
  zoom: 1.0;
}
/* general and mobile first */
html {
}
body {
  max-width: 90%;
  margin: 1.5em auto;
  color: #222;
  background-color: #fff;
  font-size: 14px;
  font-family: 'Noto Sans', Arial, Helvetica, sans-serif;
  line-height: 1.6;
  scroll-behavior: smooth;
}
.ears {
  display: none;
}

/* headings */
#title, h1, h2, h3, h4, h5, h6 {
  margin: 1em 0 0.5em;
  font-weight: bold;
  line-height: 1.3;
}
#title {
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  border-bottom: 1px solid #ddd;
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  padding: 1em 0 0.5em;
}
.author {
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}
h1 {
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}
h2 {
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h3 {
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h4 {
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h5, h6 {
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#n-copyright-notice {
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/* general structure */
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.alignRight.art-text pre {
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.alignRight {
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}
.alignRight > *:first-child {
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}
.alignRight > *:nth-child(2) {
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svg {
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.alignCenter.art-text pre {
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.alignCenter {
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.alignCenter > *:first-child {
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  */
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}

/* lists */
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}
ol ol, ul ul, ol ul, ul ol {
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}
li {
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}
.ulCompact li {
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ul.empty, .ulEmpty {
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}
ul.empty li, .ulEmpty li {
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}
ul.compact, .ulCompact,
ol.compact, .olCompact {
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  margin: 0 0 0 2em;
}

/* definition lists */
dl {
}
dl > dt {
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}
/* 
dl.nohang > dt {
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}
*/
dl > dd {
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  min-height: 1.3em;
}
dl.compact > dd, .dlCompact > dd {
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dl > dd > dl {
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  margin-bottom: 0em;
}

/* links */
a {
  text-decoration: none;
}
a[href] {
  color: #22e; /* Arlen: WCAG 2019 */
}
a[href]:hover {
  background-color: #f2f2f2;
}
figcaption a[href],
a[href].selfRef {
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}
/* XXX probably not this:
a.selfRef:hover {
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} */

/* Figures */
tt, code, pre, code {
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pre {
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}
img {
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}
figure {
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figure blockquote {
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}
figcaption {
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}
@media screen {
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}

/* aside, blockquote */
aside, blockquote {
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  padding: 1.2em 2em;
}
blockquote {
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  color: #111; /* Arlen: WCAG 2019 */
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}
cite {
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}

/* tables */
table {
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}
th, td {
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th {
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tr:nth-child(2n+1) > td {
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table caption {
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table p {
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}

/* pilcrow */
a.pilcrow {
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}
@media screen {
  aside:hover > a.pilcrow,
  p:hover > a.pilcrow,
  blockquote:hover > a.pilcrow,
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  pre:hover > a.pilcrow {
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  a.pilcrow:hover {
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}

/* misc */
hr {
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}
.bcp14 {
  font-variant: small-caps;
}

.role {
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}

/* info block */
#identifiers {
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  font-size: 0.9em;
}
#identifiers dt {
  width: 3em;
  clear: left;
}
#identifiers dd {
  float: left;
  margin-bottom: 0;
}
#identifiers .authors .author {
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}
#identifiers .authors .org {
  font-style: italic;
}

/* The prepared/rendered info at the very bottom of the page */
.docInfo {
  color: #666; /* Arlen: WCAG 2019 */
  font-size: 0.9em;
  font-style: italic;
  margin-top: 2em;
}
.docInfo .prepared {
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}
.docInfo .prepared {
  float: right;
}

/* table of contents */
#toc  {
  padding: 0.75em 0 2em 0;
  margin-bottom: 1em;
}
nav.toc ul {
  margin: 0 0.5em 0 0;
  padding: 0;
  list-style: none;
}
nav.toc li {
  line-height: 1.3em;
  margin: 0.75em 0;
  padding-left: 1.2em;
  text-indent: -1.2em;
}
/* references */
.references dt {
  text-align: right;
  font-weight: bold;
  min-width: 7em;
}
.references dd {
  margin-left: 8em;
  overflow: auto;
}

.refInstance {
  margin-bottom: 1.25em;
}

.references .ascii {
  margin-bottom: 0.25em;
}

/* index */
.index ul {
  margin: 0 0 0 1em;
  padding: 0;
  list-style: none;
}
.index ul ul {
  margin: 0;
}
.index li {
  margin: 0;
  text-indent: -2em;
  padding-left: 2em;
  padding-bottom: 5px;
}
.indexIndex {
  margin: 0.5em 0 1em;
}
.index a {
  font-weight: 700;
}
/* make the index two-column on all but the smallest screens */
@media (min-width: 600px) {
  .index ul {
    -moz-column-count: 2;
    -moz-column-gap: 20px;
  }
  .index ul ul {
    -moz-column-count: 1;
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}

/* authors */
address.vcard {
  font-style: normal;
  margin: 1em 0;
}

address.vcard .nameRole {
  font-weight: 700;
  margin-left: 0;
}
address.vcard .label {
  font-family: "Noto Sans",Arial,Helvetica,sans-serif;
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}
address.vcard .type {
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}
.alternative-contact {
  margin: 1.5em 0 1em;
}
hr.addr {
  border-top: 1px dashed;
  margin: 0;
  color: #ddd;
  max-width: calc(100% - 16px);
}

/* temporary notes */
.rfcEditorRemove::before {
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  top: 0.2em;
  right: 0.2em;
  padding: 0.2em;
  content: "The RFC Editor will remove this note";
  color: #9e2a00; /* Arlen: WCAG 2019 */
  background-color: #ffd; /* Arlen: WCAG 2019 */
}
.rfcEditorRemove {
  position: relative;
  padding-top: 1.8em;
  background-color: #ffd; /* Arlen: WCAG 2019 */
  border-radius: 3px;
}
.cref {
  background-color: #ffd; /* Arlen: WCAG 2019 */
  padding: 2px 4px;
}
.crefSource {
  font-style: italic;
}
/* alternative layout for smaller screens */
@media screen and (max-width: 1023px) {
  body {
    padding-top: 2em;
  }
  #title {
    padding: 1em 0;
  }
  h1 {
    font-size: 24px;
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  h2 {
    font-size: 20px;
    margin-top: -18px;  /* provide offset for in-page anchors */
    padding-top: 38px;
  }
  #identifiers dd {
    max-width: 60%;
  }
  #toc {
    position: fixed;
    z-index: 2;
    top: 0;
    right: 0;
    padding: 0;
    margin: 0;
    background-color: inherit;
    border-bottom: 1px solid #ccc;
  }
  #toc h2 {
    margin: -1px 0 0 0;
    padding: 4px 0 4px 6px;
    padding-right: 1em;
    min-width: 190px;
    font-size: 1.1em;
    text-align: right;
    background-color: #444;
    color: white;
    cursor: pointer;
  }
  #toc h2::before { /* css hamburger */
    float: right;
    position: relative;
    width: 1em;
    height: 1px;
    left: -164px;
    margin: 6px 0 0 0;
    background: white none repeat scroll 0 0;
    box-shadow: 0 4px 0 0 white, 0 8px 0 0 white;
    content: "";
  }
  #toc nav {
    display: none;
    padding: 0.5em 1em 1em;
    overflow: auto;
    height: calc(100vh - 48px);
    border-left: 1px solid #ddd;
  }
}

/* alternative layout for wide screens */
@media screen and (min-width: 1024px) {
  body {
    max-width: 724px;
    margin: 42px auto;
    padding-left: 1.5em;
    padding-right: 29em;
  }
  #toc {
    position: fixed;
    top: 42px;
    right: 42px;
    width: 25%;
    margin: 0;
    padding: 0 1em;
    z-index: 1;
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  #toc h2 {
    border-top: none;
    border-bottom: 1px solid #ddd;
    font-size: 1em;
    font-weight: normal;
    margin: 0;
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  #toc nav {
    display: block;
    height: calc(90vh - 84px);
    bottom: 0;
    padding: 0.5em 0 0;
    overflow: auto;
  }
  img { /* future proofing */
    max-width: 100%;
    height: auto;
  }
}

/* pagination */
@media print {
  body {

    width: 100%;
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  p {
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    widows: 3;
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  #n-copyright-notice {
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  #toc, #n-introduction {
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  #toc {
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  }
  figure, pre {
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  figure {
    overflow: scroll;
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  h1, h2, h3, h4, h5, h6 {
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  h2+*, h3+*, h4+*, h5+*, h6+* {
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  pre {
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    font-size: 10pt;
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  table {
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  td {
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}

/* This is commented out here, as the string-set: doesn't
   pass W3C validation currently */
/*
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.ears tfoot .right {
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*/

@page :first {
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    border: none;
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}

@page {
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  margin-bottom: 45mm;
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     the content depends on the document */
  /*
  @top-left {
    content: 'Internet-Draft';
    vertical-align: bottom;
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}

/* Changes introduced to fix issues found during implementation */
/* Make sure links are clickable even if overlapped by following H* */
a {
  z-index: 2;
}
/* Separate body from document info even without intervening H1 */
section {
  clear: both;
}


/* Top align author divs, to avoid names without organization dropping level with org names */
.author {
  vertical-align: top;
}

/* Leave room in document info to show Internet-Draft on one line */
#identifiers dt {
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/* Don't waste quite as much whitespace between label and value in doc info */
#identifiers dd {
  margin-left: 1em;
}

/* Give floating toc a background color (needed when it's a div inside section */
#toc {
  background-color: white;
}

/* Make the collapsed ToC header render white on gray also when it's a link */
@media screen and (max-width: 1023px) {
  #toc h2 a,
  #toc h2 a:link,
  #toc h2 a:focus,
  #toc h2 a:hover,
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    background-color: #444;
    text-decoration: none;
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}

/* Give the bottom of the ToC some whitespace */
@media screen and (min-width: 1024px) {
  #toc {
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}

/* Style section numbers with more space between number and title */
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/* prevent monospace from becoming overly large */
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/* Fix the height/width aspect for ascii art*/
pre.sourcecode,
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/* Add styling for a link in the ToC that points to the top of the document */
a.toplink {
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  margin-right: 0.5em;
}

/* Fix the dl styling to match the RFC 7992 attributes */
dl > dt,
dl.dlParallel > dt {
  float: left;
  margin-right: 1em;
}
dl.dlNewline > dt {
  float: none;
}

/* Provide styling for table cell text alignment */
table td.text-left,
table th.text-left {
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}
table td.text-center,
table th.text-center {
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}
table td.text-right,
table th.text-right {
  text-align: right;
}

/* Make the alternative author contact informatio look less like just another
   author, and group it closer with the primary author contact information */
.alternative-contact {
  margin: 0.5em 0 0.25em 0;
}
address .non-ascii {
  margin: 0 0 0 2em;
}

/* With it being possible to set tables with alignment
  left, center, and right, { width: 100%; } does not make sense */
table {
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}

/* Avoid reference text that sits in a block with very wide left margin,
   because of a long floating dt label.*/
.references dd {
  overflow: visible;
}

/* Control caption placement */
caption {
  caption-side: bottom;
}

/* Limit the width of the author address vcard, so names in right-to-left
   script don't end up on the other side of the page. */

address.vcard {
  max-width: 30em;
  margin-right: auto;
}

/* For address alignment dependent on LTR or RTL scripts */
address div.left {
  text-align: left;
}
address div.right {
  text-align: right;
}

/* Provide table alignment support.  We can't use the alignX classes above
   since they do unwanted things with caption and other styling. */
table.right {
 margin-left: auto;
 margin-right: 0;
}
table.center {
 margin-left: auto;
 margin-right: auto;
}
table.left {
 margin-left: 0;
 margin-right: auto;
}

/* Give the table caption label the same styling as the figcaption */
caption a[href] {
  color: #222;
}

@media print {
  .toplink {
    display: none;
  }

  /* avoid overwriting the top border line with the ToC header */
  #toc {
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  /* Avoid page breaks inside dl and author address entries */
  .vcard {
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}
/* Avoid wrapping of URLs in references */
@media screen {
  .references a {
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}
/* Tweak the bcp14 keyword presentation */
.bcp14 {
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  font-weight: bold;
  font-size: 0.9em;
}
/* Tweak the invisible space above H* in order not to overlay links in text above */
 h2 {
  margin-top: -18px;  /* provide offset for in-page anchors */
  padding-top: 31px;
 }
 h3 {
  margin-top: -18px;  /* provide offset for in-page anchors */
  padding-top: 24px;
 }
 h4 {
  margin-top: -18px;  /* provide offset for in-page anchors */
  padding-top: 24px;
 }
/* Float artwork pilcrow to the right */
@media screen {
  .artwork a.pilcrow {
    display: block;
    line-height: 0.7;
    margin-top: 0.15em;
  }
}
/* Make pilcrows on dd visible */
@media screen {
  dd:hover > a.pilcrow {
    visibility: visible;
  }
}
/* Make the placement of figcaption match that of a table's caption
   by removing the figure's added bottom margin */
.alignLeft.art-text,
.alignCenter.art-text,
.alignRight.art-text {
   margin-bottom: 0;
}
.alignLeft,
.alignCenter,
.alignRight {
  margin: 1em 0 0 0;
}
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<table class="ears">
<thead><tr>
<td class="left">RFC 8705</td>
<td class="center">OAuth Mutual TLS</td>
<td class="right">February 2020</td>
</tr></thead>
<tfoot><tr>
<td class="left">Campbell, et al.</td>
<td class="center">Standards Track</td>
<td class="right">[Page]</td>
</tr></tfoot>
</table>
<div id="external-metadata" class="document-information"></div>
<div id="internal-metadata" class="document-information">
<dl id="identifiers">
<dt class="label-stream">Stream:</dt>
<dd class="stream">Internet Engineering Task Force (IETF)</dd>
<dt class="label-rfc">RFC:</dt>
<dd class="rfc"><a href="https://www.rfc-editor.org/rfc/rfc8705" class="eref">8705</a></dd>
<dt class="label-category">Category:</dt>
<dd class="category">Standards Track</dd>
<dt class="label-published">Published:</dt>
<dd class="published">
<time datetime="2020-02" class="published">February 2020</time>
    </dd>
<dt class="label-issn">ISSN:</dt>
<dd class="issn">2070-1721</dd>
<dt class="label-authors">Authors:</dt>
<dd class="authors">
<div class="author">
      <div class="author-name">B. Campbell</div>
<div class="org">Ping Identity</div>
</div>
<div class="author">
      <div class="author-name">J. Bradley</div>
<div class="org">Yubico</div>
</div>
<div class="author">
      <div class="author-name">N. Sakimura</div>
<div class="org">Nomura Research Institute</div>
</div>
<div class="author">
      <div class="author-name">T. Lodderstedt</div>
<div class="org">YES.com AG</div>
</div>
</dd>
</dl>
</div>
<h1 id="rfcnum">RFC 8705</h1>
<h1 id="title">OAuth 2.0 Mutual-TLS Client Authentication and Certificate-Bound Access Tokens</h1>
<section id="section-abstract">
      <h2 id="abstract"><a href="#abstract" class="selfRef">Abstract</a></h2>
<p id="section-abstract-1">
  This document describes OAuth client authentication and certificate-bound
  access and refresh tokens using mutual Transport Layer Security (TLS)
  authentication with X.509 certificates.  OAuth clients are provided a
  mechanism for authentication to the authorization server using mutual TLS,
  based on either self-signed certificates or public key infrastructure (PKI).
  OAuth authorization servers are provided a mechanism for binding access
  tokens to a client's mutual-TLS certificate, and OAuth protected resources
  are provided a method for ensuring that such an access token presented to it
  was issued to the client presenting the token.<a href="#section-abstract-1" class="pilcrow">¶</a></p>
</section>
<div id="status-of-memo">
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        <h2 id="name-status-of-this-memo">
<a href="#name-status-of-this-memo" class="section-name selfRef">Status of This Memo</a>
        </h2>
<p id="section-boilerplate.1-1">
            This is an Internet Standards Track document.<a href="#section-boilerplate.1-1" class="pilcrow">¶</a></p>
<p id="section-boilerplate.1-2">
            This document is a product of the Internet Engineering Task Force
            (IETF).  It represents the consensus of the IETF community.  It has
            received public review and has been approved for publication by
            the Internet Engineering Steering Group (IESG).  Further
            information on Internet Standards is available in Section 2 of 
            RFC 7841.<a href="#section-boilerplate.1-2" class="pilcrow">¶</a></p>
<p id="section-boilerplate.1-3">
            Information about the current status of this document, any
            errata, and how to provide feedback on it may be obtained at
            <span><a href="https://www.rfc-editor.org/info/rfc8705">https://www.rfc-editor.org/info/rfc8705</a></span>.<a href="#section-boilerplate.1-3" class="pilcrow">¶</a></p>
</section>
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            This document is subject to BCP 78 and the IETF Trust's Legal
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            warranty as described in the Simplified BSD License.<a href="#section-boilerplate.2-2" class="pilcrow">¶</a></p>
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</div>
<div id="toc">
<section id="section-toc.1">
        <a href="#" onclick="scroll(0,0)" class="toplink">▲</a><h2 id="name-table-of-contents">
<a href="#name-table-of-contents" class="section-name selfRef">Table of Contents</a>
        </h2>
<nav class="toc"><ul class="toc ulEmpty">
<li class="toc ulEmpty" id="section-toc.1-1.1">
            <p id="section-toc.1-1.1.1"><a href="#section-1" class="xref">1</a>.  <a href="#name-introduction" class="xref">Introduction</a><a href="#section-toc.1-1.1.1" class="pilcrow">¶</a></p>
<ul class="toc ulEmpty">
<li class="toc ulEmpty" id="section-toc.1-1.1.2.1">
                <p id="section-toc.1-1.1.2.1.1"><a href="#section-1.1" class="xref">1.1</a>.  <a href="#name-requirements-notation-and-c" class="xref">Requirements Notation and Conventions</a><a href="#section-toc.1-1.1.2.1.1" class="pilcrow">¶</a></p>
</li>
<li class="toc ulEmpty" id="section-toc.1-1.1.2.2">
                <p id="section-toc.1-1.1.2.2.1"><a href="#section-1.2" class="xref">1.2</a>.  <a href="#name-terminology" class="xref">Terminology</a><a href="#section-toc.1-1.1.2.2.1" class="pilcrow">¶</a></p>
</li>
</ul>
</li>
<li class="toc ulEmpty" id="section-toc.1-1.2">
            <p id="section-toc.1-1.2.1"><a href="#section-2" class="xref">2</a>.  <a href="#name-mutual-tls-for-oauth-client" class="xref">Mutual TLS for OAuth Client Authentication</a><a href="#section-toc.1-1.2.1" class="pilcrow">¶</a></p>
<ul class="toc ulEmpty">
<li class="toc ulEmpty" id="section-toc.1-1.2.2.1">
                <p id="section-toc.1-1.2.2.1.1"><a href="#section-2.1" class="xref">2.1</a>.  <a href="#name-pki-mutual-tls-method" class="xref">PKI Mutual-TLS Method</a><a href="#section-toc.1-1.2.2.1.1" class="pilcrow">¶</a></p>
<ul class="toc ulEmpty">
<li class="toc ulEmpty" id="section-toc.1-1.2.2.1.2.1">
                    <p id="section-toc.1-1.2.2.1.2.1.1"><a href="#section-2.1.1" class="xref">2.1.1</a>.  <a href="#name-pki-method-metadata-value" class="xref">PKI Method Metadata Value</a><a href="#section-toc.1-1.2.2.1.2.1.1" class="pilcrow">¶</a></p>
</li>
<li class="toc ulEmpty" id="section-toc.1-1.2.2.1.2.2">
                    <p id="section-toc.1-1.2.2.1.2.2.1"><a href="#section-2.1.2" class="xref">2.1.2</a>.  <a href="#name-client-registration-metadat" class="xref">Client Registration Metadata</a><a href="#section-toc.1-1.2.2.1.2.2.1" class="pilcrow">¶</a></p>
</li>
</ul>
</li>
<li class="toc ulEmpty" id="section-toc.1-1.2.2.2">
                <p id="section-toc.1-1.2.2.2.1"><a href="#section-2.2" class="xref">2.2</a>.  <a href="#name-self-signed-certificate-mut" class="xref">Self-Signed Certificate Mutual-TLS Method</a><a href="#section-toc.1-1.2.2.2.1" class="pilcrow">¶</a></p>
<ul class="toc ulEmpty">
<li class="toc ulEmpty" id="section-toc.1-1.2.2.2.2.1">
                    <p id="section-toc.1-1.2.2.2.2.1.1"><a href="#section-2.2.1" class="xref">2.2.1</a>.  <a href="#name-self-signed-method-metadata" class="xref">Self-Signed Method Metadata Value</a><a href="#section-toc.1-1.2.2.2.2.1.1" class="pilcrow">¶</a></p>
</li>
<li class="toc ulEmpty" id="section-toc.1-1.2.2.2.2.2">
                    <p id="section-toc.1-1.2.2.2.2.2.1"><a href="#section-2.2.2" class="xref">2.2.2</a>.  <a href="#name-client-registration-metadata" class="xref">Client Registration Metadata</a><a href="#section-toc.1-1.2.2.2.2.2.1" class="pilcrow">¶</a></p>
</li>
</ul>
</li>
</ul>
</li>
<li class="toc ulEmpty" id="section-toc.1-1.3">
            <p id="section-toc.1-1.3.1"><a href="#section-3" class="xref">3</a>.  <a href="#name-mutual-tls-client-certifica" class="xref">Mutual-TLS Client Certificate-Bound Access Tokens</a><a href="#section-toc.1-1.3.1" class="pilcrow">¶</a></p>
<ul class="toc ulEmpty">
<li class="toc ulEmpty" id="section-toc.1-1.3.2.1">
                <p id="section-toc.1-1.3.2.1.1"><a href="#section-3.1" class="xref">3.1</a>.  <a href="#name-jwt-certificate-thumbprint-" class="xref">JWT Certificate Thumbprint Confirmation Method</a><a href="#section-toc.1-1.3.2.1.1" class="pilcrow">¶</a></p>
</li>
<li class="toc ulEmpty" id="section-toc.1-1.3.2.2">
                <p id="section-toc.1-1.3.2.2.1"><a href="#section-3.2" class="xref">3.2</a>.  <a href="#name-confirmation-method-for-tok" class="xref">Confirmation Method for Token Introspection</a><a href="#section-toc.1-1.3.2.2.1" class="pilcrow">¶</a></p>
</li>
<li class="toc ulEmpty" id="section-toc.1-1.3.2.3">
                <p id="section-toc.1-1.3.2.3.1"><a href="#section-3.3" class="xref">3.3</a>.  <a href="#name-authorization-server-metada" class="xref">Authorization Server Metadata</a><a href="#section-toc.1-1.3.2.3.1" class="pilcrow">¶</a></p>
</li>
<li class="toc ulEmpty" id="section-toc.1-1.3.2.4">
                <p id="section-toc.1-1.3.2.4.1"><a href="#section-3.4" class="xref">3.4</a>.  <a href="#name-client-registration-metadata-2" class="xref">Client Registration Metadata</a><a href="#section-toc.1-1.3.2.4.1" class="pilcrow">¶</a></p>
</li>
</ul>
</li>
<li class="toc ulEmpty" id="section-toc.1-1.4">
            <p id="section-toc.1-1.4.1"><a href="#section-4" class="xref">4</a>.  <a href="#name-public-clients-and-certific" class="xref">Public Clients and Certificate-Bound Tokens</a><a href="#section-toc.1-1.4.1" class="pilcrow">¶</a></p>
</li>
<li class="toc ulEmpty" id="section-toc.1-1.5">
            <p id="section-toc.1-1.5.1"><a href="#section-5" class="xref">5</a>.  <a href="#name-metadata-for-mutual-tls-end" class="xref">Metadata for Mutual-TLS Endpoint Aliases</a><a href="#section-toc.1-1.5.1" class="pilcrow">¶</a></p>
</li>
<li class="toc ulEmpty" id="section-toc.1-1.6">
            <p id="section-toc.1-1.6.1"><a href="#section-6" class="xref">6</a>.  <a href="#name-implementation-consideratio" class="xref">Implementation Considerations</a><a href="#section-toc.1-1.6.1" class="pilcrow">¶</a></p>
<ul class="toc ulEmpty">
<li class="toc ulEmpty" id="section-toc.1-1.6.2.1">
                <p id="section-toc.1-1.6.2.1.1"><a href="#section-6.1" class="xref">6.1</a>.  <a href="#name-authorization-server" class="xref">Authorization Server</a><a href="#section-toc.1-1.6.2.1.1" class="pilcrow">¶</a></p>
</li>
<li class="toc ulEmpty" id="section-toc.1-1.6.2.2">
                <p id="section-toc.1-1.6.2.2.1"><a href="#section-6.2" class="xref">6.2</a>.  <a href="#name-resource-server" class="xref">Resource Server</a><a href="#section-toc.1-1.6.2.2.1" class="pilcrow">¶</a></p>
</li>
<li class="toc ulEmpty" id="section-toc.1-1.6.2.3">
                <p id="section-toc.1-1.6.2.3.1"><a href="#section-6.3" class="xref">6.3</a>.  <a href="#name-certificate-expiration-and-" class="xref">Certificate Expiration and Bound Access Tokens</a><a href="#section-toc.1-1.6.2.3.1" class="pilcrow">¶</a></p>
</li>
<li class="toc ulEmpty" id="section-toc.1-1.6.2.4">
                <p id="section-toc.1-1.6.2.4.1"><a href="#section-6.4" class="xref">6.4</a>.  <a href="#name-implicit-grant-unsupported" class="xref">Implicit Grant Unsupported</a><a href="#section-toc.1-1.6.2.4.1" class="pilcrow">¶</a></p>
</li>
<li class="toc ulEmpty" id="section-toc.1-1.6.2.5">
                <p id="section-toc.1-1.6.2.5.1"><a href="#section-6.5" class="xref">6.5</a>.  <a href="#name-tls-termination" class="xref">TLS Termination</a><a href="#section-toc.1-1.6.2.5.1" class="pilcrow">¶</a></p>
</li>
</ul>
</li>
<li class="toc ulEmpty" id="section-toc.1-1.7">
            <p id="section-toc.1-1.7.1"><a href="#section-7" class="xref">7</a>.  <a href="#name-security-considerations" class="xref">Security Considerations</a><a href="#section-toc.1-1.7.1" class="pilcrow">¶</a></p>
<ul class="toc ulEmpty">
<li class="toc ulEmpty" id="section-toc.1-1.7.2.1">
                <p id="section-toc.1-1.7.2.1.1"><a href="#section-7.1" class="xref">7.1</a>.  <a href="#name-certificate-bound-refresh-t" class="xref">Certificate-Bound Refresh Tokens</a><a href="#section-toc.1-1.7.2.1.1" class="pilcrow">¶</a></p>
</li>
<li class="toc ulEmpty" id="section-toc.1-1.7.2.2">
                <p id="section-toc.1-1.7.2.2.1"><a href="#section-7.2" class="xref">7.2</a>.  <a href="#name-certificate-thumbprint-bind" class="xref">Certificate Thumbprint Binding</a><a href="#section-toc.1-1.7.2.2.1" class="pilcrow">¶</a></p>
</li>
<li class="toc ulEmpty" id="section-toc.1-1.7.2.3">
                <p id="section-toc.1-1.7.2.3.1"><a href="#section-7.3" class="xref">7.3</a>.  <a href="#name-tls-versions-and-best-pract" class="xref">TLS Versions and Best Practices</a><a href="#section-toc.1-1.7.2.3.1" class="pilcrow">¶</a></p>
</li>
<li class="toc ulEmpty" id="section-toc.1-1.7.2.4">
                <p id="section-toc.1-1.7.2.4.1"><a href="#section-7.4" class="xref">7.4</a>.  <a href="#name-x509-certificate-spoofing" class="xref">X.509 Certificate Spoofing</a><a href="#section-toc.1-1.7.2.4.1" class="pilcrow">¶</a></p>
</li>
<li class="toc ulEmpty" id="section-toc.1-1.7.2.5">
                <p id="section-toc.1-1.7.2.5.1"><a href="#section-7.5" class="xref">7.5</a>.  <a href="#name-x509-certificate-parsing-an" class="xref">X.509 Certificate Parsing and Validation Complexity</a><a href="#section-toc.1-1.7.2.5.1" class="pilcrow">¶</a></p>
</li>
</ul>
</li>
<li class="toc ulEmpty" id="section-toc.1-1.8">
            <p id="section-toc.1-1.8.1"><a href="#section-8" class="xref">8</a>.  <a href="#name-privacy-considerations" class="xref">Privacy Considerations</a><a href="#section-toc.1-1.8.1" class="pilcrow">¶</a></p>
</li>
<li class="toc ulEmpty" id="section-toc.1-1.9">
            <p id="section-toc.1-1.9.1"><a href="#section-9" class="xref">9</a>.  <a href="#name-iana-considerations" class="xref">IANA Considerations</a><a href="#section-toc.1-1.9.1" class="pilcrow">¶</a></p>
<ul class="toc ulEmpty">
<li class="toc ulEmpty" id="section-toc.1-1.9.2.1">
                <p id="section-toc.1-1.9.2.1.1"><a href="#section-9.1" class="xref">9.1</a>.  <a href="#name-jwt-confirmation-methods-re" class="xref">JWT Confirmation Methods Registration</a><a href="#section-toc.1-1.9.2.1.1" class="pilcrow">¶</a></p>
</li>
<li class="toc ulEmpty" id="section-toc.1-1.9.2.2">
                <p id="section-toc.1-1.9.2.2.1"><a href="#section-9.2" class="xref">9.2</a>.  <a href="#name-authorization-server-metadat" class="xref">Authorization Server Metadata Registration</a><a href="#section-toc.1-1.9.2.2.1" class="pilcrow">¶</a></p>
</li>
<li class="toc ulEmpty" id="section-toc.1-1.9.2.3">
                <p id="section-toc.1-1.9.2.3.1"><a href="#section-9.3" class="xref">9.3</a>.  <a href="#name-token-endpoint-authenticati" class="xref">Token Endpoint Authentication Method Registration</a><a href="#section-toc.1-1.9.2.3.1" class="pilcrow">¶</a></p>
</li>
<li class="toc ulEmpty" id="section-toc.1-1.9.2.4">
                <p id="section-toc.1-1.9.2.4.1"><a href="#section-9.4" class="xref">9.4</a>.  <a href="#name-token-introspection-respons" class="xref">Token Introspection Response Registration</a><a href="#section-toc.1-1.9.2.4.1" class="pilcrow">¶</a></p>
</li>
<li class="toc ulEmpty" id="section-toc.1-1.9.2.5">
                <p id="section-toc.1-1.9.2.5.1"><a href="#section-9.5" class="xref">9.5</a>.  <a href="#name-dynamic-client-registration" class="xref">Dynamic Client Registration Metadata Registration</a><a href="#section-toc.1-1.9.2.5.1" class="pilcrow">¶</a></p>
</li>
</ul>
</li>
<li class="toc ulEmpty" id="section-toc.1-1.10">
            <p id="section-toc.1-1.10.1"><a href="#section-10" class="xref">10</a>. <a href="#name-references" class="xref">References</a><a href="#section-toc.1-1.10.1" class="pilcrow">¶</a></p>
<ul class="toc ulEmpty">
<li class="toc ulEmpty" id="section-toc.1-1.10.2.1">
                <p id="section-toc.1-1.10.2.1.1"><a href="#section-10.1" class="xref">10.1</a>.  <a href="#name-normative-references" class="xref">Normative References</a><a href="#section-toc.1-1.10.2.1.1" class="pilcrow">¶</a></p>
</li>
<li class="toc ulEmpty" id="section-toc.1-1.10.2.2">
                <p id="section-toc.1-1.10.2.2.1"><a href="#section-10.2" class="xref">10.2</a>.  <a href="#name-informative-references" class="xref">Informative References</a><a href="#section-toc.1-1.10.2.2.1" class="pilcrow">¶</a></p>
</li>
</ul>
</li>
<li class="toc ulEmpty" id="section-toc.1-1.11">
            <p id="section-toc.1-1.11.1"><a href="#section-appendix.a" class="xref">Appendix A</a>.  <a href="#name-example-cnf-claim-certifica" class="xref">Example "cnf" Claim, Certificate, and JWK</a><a href="#section-toc.1-1.11.1" class="pilcrow">¶</a></p>
</li>
<li class="toc ulEmpty" id="section-toc.1-1.12">
            <p id="section-toc.1-1.12.1"><a href="#section-appendix.b" class="xref">Appendix B</a>.  <a href="#name-relationship-to-token-bindi" class="xref">Relationship to Token Binding</a><a href="#section-toc.1-1.12.1" class="pilcrow">¶</a></p>
</li>
<li class="toc ulEmpty" id="section-toc.1-1.13">
            <p id="section-toc.1-1.13.1"><a href="#section-appendix.c" class="xref"></a><a href="#name-acknowledgements" class="xref">Acknowledgements</a><a href="#section-toc.1-1.13.1" class="pilcrow">¶</a></p>
</li>
<li class="toc ulEmpty" id="section-toc.1-1.14">
            <p id="section-toc.1-1.14.1"><a href="#section-appendix.d" class="xref"></a><a href="#name-authors-addresses" class="xref">Authors' Addresses</a><a href="#section-toc.1-1.14.1" class="pilcrow">¶</a></p>
</li>
</ul>
</nav>
</section>
</div>
<div id="Introduction">
<section id="section-1">
      <h2 id="name-introduction">
<a href="#section-1" class="section-number selfRef">1. </a><a href="#name-introduction" class="section-name selfRef">Introduction</a>
      </h2>
<p id="section-1-1">
  The OAuth 2.0 Authorization Framework <span>[<a href="#RFC6749" class="xref">RFC6749</a>]</span> enables third-party
  client applications to obtain delegated access to protected resources.
  In the prototypical abstract OAuth flow, illustrated in <a href="#protocol-flow-figure" class="xref">Figure 1</a>,
  the client obtains an access token from an entity known as an
  authorization server and then uses that token when accessing protected resources,
  such as HTTPS APIs.<a href="#section-1-1" class="pilcrow">¶</a></p>
<span id="name-abstract-oauth-20-protocol-"></span><div id="protocol-flow-figure">
<figure id="figure-1">
        <div class="artwork art-text alignLeft" id="section-1-2.1">
<pre>
  +--------+                                 +---------------+
  |        |                                 |               |
  |        |&lt;--(A)-- Get an access token ---&gt;| Authorization |
  |        |                                 |     Server    |
  |        |                                 |               |
  |        |                                 +---------------+
  |        |                                         ^
  |        |                                         |
  |        |
  |        |                               (C)       |
  | Client |                           Validate the
  |        |                           access token  |
  |        |
  |        |                                         |
  |        |                                         v
  |        |                                 +---------------+
  |        |                                 |      (C)      |
  |        |                                 |               |
  |        |&lt;--(B)-- Use the access token --&gt;|   Protected   |
  |        |                                 |    Resource   |
  |        |                                 |               |
  +--------+                                 +---------------+
</pre>
</div>
<figcaption><a href="#figure-1" class="selfRef">Figure 1</a>:
<a href="#name-abstract-oauth-20-protocol-" class="selfRef">Abstract OAuth 2.0 Protocol Flow</a>
        </figcaption></figure>
</div>
<p id="section-1-3">
  The flow illustrated in <a href="#protocol-flow-figure" class="xref">Figure 1</a> includes the following steps:<a href="#section-1-3" class="pilcrow">¶</a></p>
<dl class="olPercent" id="section-1-4">
        <dt>(A)</dt>
<dd style="margin-left: 2.5em" id="section-1-4.1">
      The client makes an HTTPS <code>POST</code> request to
      the authorization server and presents
      a credential representing the authorization grant. For
      certain types of clients (those that have been issued or otherwise established
      a set of client credentials) the request must be authenticated.
      In the response, the authorization server issues an access token to the client.<a href="#section-1-4.1" class="pilcrow">¶</a>
</dd>
<dt>(B)</dt>
<dd style="margin-left: 2.5em" id="section-1-4.2">
      The client includes the access token when making a request to access a protected resource.<a href="#section-1-4.2" class="pilcrow">¶</a>
</dd>
<dt>(C)</dt>
<dd style="margin-left: 2.5em" id="section-1-4.3">
      The protected resource validates the access token in order to authorize the request.
      In some cases, such as when the token is self-contained and cryptographically secured,
      the validation can be done locally by the protected resource.  Other cases require
      that the protected resource call out to the authorization server to determine the state
      of the token and obtain metainformation about it.<a href="#section-1-4.3" class="pilcrow">¶</a>
</dd>
</dl>
<p id="section-1-5">
  Layering on the abstract flow above, this document standardizes enhanced
  security options for OAuth 2.0 utilizing client-certificate-based mutual
  TLS. <a href="#mtlsca" class="xref">Section 2</a> provides options for
  authenticating the request in Step
  (A). Step (C) is supported with semantics
  to express the binding of the token to the client certificate for both local
  and remote processing in Sections <a href="#x5t" class="xref">3.1</a> and
  <a href="#introspect" class="xref">3.2</a>, respectively. This ensures
  that, as described in <a href="#CertificateBoundAccessTokens" class="xref">Section 3</a>, protected resource access in Step
  (B) is only possible by the legitimate client using a
  certificate-bound token and holding the private key corresponding to the
  certificate.<a href="#section-1-5" class="pilcrow">¶</a></p>
<p id="section-1-6">
  OAuth 2.0
  defines a shared-secret method of client authentication but also
  allows for defining and using additional client authentication mechanisms
  when interacting directly with the authorization server.
  This document describes an additional mechanism of client authentication utilizing
  mutual-TLS certificate-based authentication that provides
  better security characteristics than shared secrets.
  While <span>[<a href="#RFC6749" class="xref">RFC6749</a>]</span> documents client authentication for requests to the token endpoint,
  extensions to OAuth 2.0 (such as Introspection <span>[<a href="#RFC7662" class="xref">RFC7662</a>]</span>,
  Revocation <span>[<a href="#RFC7009" class="xref">RFC7009</a>]</span>, and the Backchannel Authentication Endpoint
  in <span>[<a href="#OpenID.CIBA" class="xref">OpenID.CIBA</a>]</span>) define endpoints that also utilize client authentication,
  and the mutual-TLS methods defined herein are applicable to those endpoints as well.<a href="#section-1-6" class="pilcrow">¶</a></p>
<p id="section-1-7">
  Mutual-TLS certificate-bound access tokens ensure that
  only the party in possession of the
  private key corresponding to the certificate can utilize the token to
  access the associated resources. Such a constraint is
  sometimes referred to as key confirmation, proof-of-possession, or holder-of-key
  and is unlike the case of the
  bearer token described in <span>[<a href="#RFC6750" class="xref">RFC6750</a>]</span>, where any party in
  possession of the access token can use it to access the associated resources.
  Binding an access token to the client's certificate
  prevents the use of stolen access tokens or replay of access tokens
  by unauthorized parties.<a href="#section-1-7" class="pilcrow">¶</a></p>
<p id="section-1-8">
  Mutual-TLS certificate-bound access tokens and mutual-TLS client authentication
  are distinct mechanisms that are complementary but don't necessarily need to be deployed or used together.<a href="#section-1-8" class="pilcrow">¶</a></p>
<p id="section-1-9">
  Additional client metadata parameters are introduced by this document in support of
  certificate-bound access tokens and mutual-TLS client authentication.
  The authorization server can obtain client metadata via the
  Dynamic Client Registration Protocol <span>[<a href="#RFC7591" class="xref">RFC7591</a>]</span>, which defines mechanisms for dynamically registering
  OAuth 2.0 client metadata with authorization servers.
  Also the metadata defined by <span>[<a href="#RFC7591" class="xref">RFC7591</a>]</span>, and registered extensions to
  it, imply a general data model for clients that is useful for
  authorization server implementations, even when the Dynamic Client
  Registration Protocol isn't in play. Such implementations will typically have
  some sort of user interface available for managing client configuration.<a href="#section-1-9" class="pilcrow">¶</a></p>
<div id="RNC">
<section id="section-1.1">
        <h3 id="name-requirements-notation-and-c">
<a href="#section-1.1" class="section-number selfRef">1.1. </a><a href="#name-requirements-notation-and-c" class="section-name selfRef">Requirements Notation and Conventions</a>
        </h3>
<p id="section-1.1-1">
    The key words "<span class="bcp14">MUST</span>", "<span class="bcp14">MUST NOT</span>", "<span class="bcp14">REQUIRED</span>", "<span class="bcp14">SHALL</span>", "<span class="bcp14">SHALL NOT</span>", "<span class="bcp14">SHOULD</span>", "<span class="bcp14">SHOULD NOT</span>", "<span class="bcp14">RECOMMENDED</span>", "<span class="bcp14">NOT RECOMMENDED</span>",
    "<span class="bcp14">MAY</span>", and "<span class="bcp14">OPTIONAL</span>" in this document are to be interpreted as
    described in BCP 14 <span>[<a href="#RFC2119" class="xref">RFC2119</a>]</span> <span>[<a href="#RFC8174" class="xref">RFC8174</a>]</span> 
    when, and only when, they appear in all capitals, as shown here.<a href="#section-1.1-1" class="pilcrow">¶</a></p>
</section>
</div>
<div id="Terminology">
<section id="section-1.2">
        <h3 id="name-terminology">
<a href="#section-1.2" class="section-number selfRef">1.2. </a><a href="#name-terminology" class="section-name selfRef">Terminology</a>
        </h3>
<p id="section-1.2-1">
  Throughout this document the term "mutual TLS" refers to the process whereby, in addition to the normal TLS
  server authentication with a certificate, a client presents its X.509 certificate
  and proves possession of the corresponding private key to a server when negotiating a TLS session.

  In contemporary versions of TLS <span>[<a href="#RFC5246" class="xref">RFC5246</a>]</span> <span>[<a href="#RFC8446" class="xref">RFC8446</a>]</span>, this requires that the client send
  the Certificate and CertificateVerify messages during the handshake and
  for the server to verify the CertificateVerify and Finished messages.<a href="#section-1.2-1" class="pilcrow">¶</a></p>
</section>
</div>
</section>
</div>
<div id="mtlsca">
<section id="section-2">
      <h2 id="name-mutual-tls-for-oauth-client">
<a href="#section-2" class="section-number selfRef">2. </a><a href="#name-mutual-tls-for-oauth-client" class="section-name selfRef">Mutual TLS for OAuth Client Authentication</a>
      </h2>
<p id="section-2-1">
  This section defines, as an extension of 
  <span><a href="https://www.rfc-editor.org/rfc/rfc6749#section-2.3" class="relref">Section 2.3</a> of OAuth 2.0 [<a href="#RFC6749" class="xref">RFC6749</a>]</span>, two distinct methods of using
  mutual-TLS X.509 client certificates as client credentials.
  The requirement of mutual TLS for client authentication is determined by the authorization server,
  based on policy or configuration for the given client (regardless of whether the client was dynamically
  registered, statically configured, or otherwise established).<a href="#section-2-1" class="pilcrow">¶</a></p>
<p id="section-2-2">
  In order to utilize TLS for OAuth client authentication, the TLS
  connection between the client and the authorization server <span class="bcp14">MUST</span> have been established or re-established
  with mutual-TLS X.509 certificate authentication
  (i.e., the client Certificate and CertificateVerify messages are sent during
  the TLS handshake).<a href="#section-2-2" class="pilcrow">¶</a></p>
<p id="section-2-3">
  For all requests to the authorization server utilizing mutual-TLS client
  authentication, the client <span class="bcp14">MUST</span> include the
  <code>client_id</code> parameter described in <span><a href="https://www.rfc-editor.org/rfc/rfc6749#section-2.2" class="relref">Section 2.2</a> of OAuth 2.0 [<a href="#RFC6749" class="xref">RFC6749</a>]</span>.  The presence of the
  <code>client_id</code> parameter enables the authorization server to easily
  identify the client independently from the content of the certificate. The
  authorization server can locate the client configuration using the client
  identifier and check the certificate presented in the TLS handshake against
  the expected credentials for that client.  The authorization server
  <span class="bcp14">MUST</span> enforce the binding between client and certificate, as
  described in either Section <a href="#pki_method" class="xref">2.1</a> or <a href="#self_signed_method" class="xref">2.2</a> below.  If no certificate is
  presented, or that which is presented doesn't match that which is expected
  for the given <code>client_id</code>, the authorization server returns a normal
  OAuth 2.0 error response per <span><a href="https://www.rfc-editor.org/rfc/rfc6749#section-5.2" class="relref">Section 5.2</a> of [<a href="#RFC6749" class="xref">RFC6749</a>]</span> with the <code>invalid_client</code> error code to
  indicate failed client authentication.<a href="#section-2-3" class="pilcrow">¶</a></p>
<div id="pki_method">
<section id="section-2.1">
        <h3 id="name-pki-mutual-tls-method">
<a href="#section-2.1" class="section-number selfRef">2.1. </a><a href="#name-pki-mutual-tls-method" class="section-name selfRef">PKI Mutual-TLS Method</a>
        </h3>
<p id="section-2.1-1">
        The PKI (public key infrastructure) method of mutual-TLS OAuth client authentication
        adheres to the way in which X.509 certificates are traditionally used
        for authentication. It relies on a validated certificate chain <span>[<a href="#RFC5280" class="xref">RFC5280</a>]</span>
        and a single subject distinguished name (DN) or a single
        subject alternative name (SAN) to authenticate the client.
        Only one subject name value of any type is used for each client.
        The TLS handshake is utilized to validate the client's possession
        of the private key corresponding to the public key in the certificate and to
        validate the corresponding certificate chain. The client is successfully authenticated
        if the subject information in the certificate matches the single expected subject configured or
        registered for that particular client
        (note that a predictable treatment of DN values, such as the distinguishedNameMatch
        rule from <span>[<a href="#RFC4517" class="xref">RFC4517</a>]</span>, is needed in comparing the
        certificate's subject DN to the client's registered DN).
        Revocation checking is possible with the PKI method but if and how to check a certificate's
        revocation status is a deployment decision at the discretion of the authorization server.
        Clients can rotate their X.509 certificates
        without the need to modify the respective authentication data at the authorization
        server by obtaining a new certificate with the same subject from a trusted certificate authority (CA).<a href="#section-2.1-1" class="pilcrow">¶</a></p>
<div id="metadata_auth_value_pki">
<section id="section-2.1.1">
          <h4 id="name-pki-method-metadata-value">
<a href="#section-2.1.1" class="section-number selfRef">2.1.1. </a><a href="#name-pki-method-metadata-value" class="section-name selfRef">PKI Method Metadata Value</a>
          </h4>
<p id="section-2.1.1-1">
          For the PKI method of mutual-TLS client authentication, this specification
          defines and registers the following authentication method metadata
          value into the "OAuth Token Endpoint Authentication Methods" registry
          <span>[<a href="#IANA.OAuth.Parameters" class="xref">IANA.OAuth.Parameters</a>]</span>.<a href="#section-2.1.1-1" class="pilcrow">¶</a></p>
<dl class="dlNewline" id="section-2.1.1-2">
            <dt id="section-2.1.1-2.1">tls_client_auth</dt>
<dd id="section-2.1.1-2.2">
              Indicates that client authentication to the authorization server will occur with
              mutual TLS utilizing the PKI method of associating a certificate to a client.<a href="#section-2.1.1-2.2" class="pilcrow">¶</a>
</dd>
</dl>
</section>
</div>
<div id="client_metadata_pki">
<section id="section-2.1.2">
          <h4 id="name-client-registration-metadat">
<a href="#section-2.1.2" class="section-number selfRef">2.1.2. </a><a href="#name-client-registration-metadat" class="section-name selfRef">Client Registration Metadata</a>
          </h4>
<p id="section-2.1.2-1">
          In order to convey the expected subject of the certificate,
          the following metadata
          parameters are introduced for the
          OAuth 2.0 Dynamic Client Registration Protocol <span>[<a href="#RFC7591" class="xref">RFC7591</a>]</span> in support of
          the PKI method of mutual-TLS client authentication.
          A client using the <code>tls_client_auth</code> authentication method <span class="bcp14">MUST</span> use
          exactly one of the below metadata parameters to indicate the certificate subject value that
          the authorization server is to expect when authenticating the respective client.<a href="#section-2.1.2-1" class="pilcrow">¶</a></p>
<dl class="dlNewline" id="section-2.1.2-2">
            <dt id="section-2.1.2-2.1">tls_client_auth_subject_dn</dt>
<dd id="section-2.1.2-2.2">
              A string representation -- as defined in <span>[<a href="#RFC4514" class="xref">RFC4514</a>]</span> -- of the expected subject distinguished
              name of the certificate that the OAuth client will use in mutual-TLS authentication.<a href="#section-2.1.2-2.2" class="pilcrow">¶</a>
</dd>
<dt id="section-2.1.2-2.3">tls_client_auth_san_dns</dt>
<dd id="section-2.1.2-2.4">
              A string containing the value of an expected dNSName SAN entry
              in the certificate that the OAuth client will use in mutual-TLS
              authentication.<a href="#section-2.1.2-2.4" class="pilcrow">¶</a>
</dd>
<dt id="section-2.1.2-2.5">tls_client_auth_san_uri</dt>
<dd id="section-2.1.2-2.6">
              A string containing the value of an expected
              uniformResourceIdentifier SAN entry in the certificate that
              the OAuth client will use in mutual-TLS authentication.<a href="#section-2.1.2-2.6" class="pilcrow">¶</a>
</dd>
<dt id="section-2.1.2-2.7">tls_client_auth_san_ip</dt>
<dd id="section-2.1.2-2.8">
              A string representation of an IP address in either dotted
              decimal notation (for IPv4) or colon-delimited hexadecimal (for
              IPv6, as defined in <span>[<a href="#RFC5952" class="xref">RFC5952</a>]</span>)
              that is expected to be present as an iPAddress SAN entry in the
              certificate that the OAuth client will use in mutual-TLS
              authentication. Per <span><a href="https://www.rfc-editor.org/rfc/rfc5952#section-8" class="relref">Section 8</a> of [<a href="#RFC5952" class="xref">RFC5952</a>]</span>, the IP address comparison of the value in
              this parameter and the SAN entry in the certificate is to be
              done in binary format.<a href="#section-2.1.2-2.8" class="pilcrow">¶</a>
</dd>
<dt id="section-2.1.2-2.9">tls_client_auth_san_email</dt>
<dd id="section-2.1.2-2.10">
              A string containing the value of an expected rfc822Name SAN
              entry in the certificate that the OAuth client will use in
              mutual-TLS authentication.<a href="#section-2.1.2-2.10" class="pilcrow">¶</a>
</dd>
</dl>
</section>
</div>
</section>
</div>
<div id="self_signed_method">
<section id="section-2.2">
        <h3 id="name-self-signed-certificate-mut">
<a href="#section-2.2" class="section-number selfRef">2.2. </a><a href="#name-self-signed-certificate-mut" class="section-name selfRef">Self-Signed Certificate Mutual-TLS Method</a>
        </h3>
<p id="section-2.2-1">
        This method of mutual-TLS OAuth client authentication
        is intended to support client authentication using self-signed certificates.
        As a prerequisite, the client registers its X.509 certificates
        (using <code>jwks</code> defined in <span>[<a href="#RFC7591" class="xref">RFC7591</a>]</span>) or a reference to a trusted source
        for its X.509 certificates (using <code>jwks_uri</code> from <span>[<a href="#RFC7591" class="xref">RFC7591</a>]</span>)
        with the authorization server. During authentication,
        TLS is utilized to validate the client's possession of the private key
        corresponding to the public key presented within the certificate in the respective TLS handshake. In
        contrast to the PKI method, the client's certificate chain is not validated by the server in this case.
        The client is successfully authenticated if the
        certificate that it presented during the handshake matches one of the certificates
        configured or registered for that particular client.
        The Self-Signed Certificate method allows the use of mutual TLS to authenticate clients without
        the need to maintain a PKI. When used in conjunction with a <code>jwks_uri</code> for the
        client, it also allows the client to rotate its X.509 certificates without the
        need to change its respective authentication data directly with the authorization server.<a href="#section-2.2-1" class="pilcrow">¶</a></p>
<div id="metadata_auth_value_self_signed">
<section id="section-2.2.1">
          <h4 id="name-self-signed-method-metadata">
<a href="#section-2.2.1" class="section-number selfRef">2.2.1. </a><a href="#name-self-signed-method-metadata" class="section-name selfRef">Self-Signed Method Metadata Value</a>
          </h4>
<p id="section-2.2.1-1">
          For the Self-Signed Certificate method of mutual-TLS client authentication, this specification
          defines and registers the following authentication method metadata
          value into the "OAuth Token Endpoint Authentication Methods" registry
          <span>[<a href="#IANA.OAuth.Parameters" class="xref">IANA.OAuth.Parameters</a>]</span>.<a href="#section-2.2.1-1" class="pilcrow">¶</a></p>
<dl class="dlNewline" id="section-2.2.1-2">
            <dt id="section-2.2.1-2.1">self_signed_tls_client_auth</dt>
<dd id="section-2.2.1-2.2">
              Indicates that client authentication to the authorization server will occur using
              mutual TLS with the client utilizing a self-signed certificate.<a href="#section-2.2.1-2.2" class="pilcrow">¶</a>
</dd>
</dl>
</section>
</div>
<div id="client_metadata_self_signed">
<section id="section-2.2.2">
          <h4 id="name-client-registration-metadata">
<a href="#section-2.2.2" class="section-number selfRef">2.2.2. </a><a href="#name-client-registration-metadata" class="section-name selfRef">Client Registration Metadata</a>
          </h4>
<p id="section-2.2.2-1">
          For the Self-Signed Certificate method of binding a certificate with
          a client using mutual-TLS client authentication, the existing
          <code>jwks_uri</code> or <code>jwks</code> metadata parameters from <span>[<a href="#RFC7591" class="xref">RFC7591</a>]</span> are used to convey the client's
          certificates via JSON Web Key (JWK) in a JWK Set <span>[<a href="#RFC7517" class="xref">RFC7517</a>]</span>. The <code>jwks</code> metadata
          parameter is a JWK Set containing the client's public keys as an
          array of JWKs, while the <code>jwks_uri</code> parameter is a URL that
          references a client's JWK Set. A certificate is represented with
          the <code>x5c</code> parameter of an individual JWK within the set.
          Note that the members of the JWK representing the public key
          (e.g., "n" and "e" for RSA, "x" and "y" for Elliptic Curve (EC)) are required
          parameters per <span>[<a href="#RFC7518" class="xref">RFC7518</a>]</span> so will be
          present even though they are not utilized in this context. Also note
          that <span><a href="https://www.rfc-editor.org/rfc/rfc7517#section-4.7" class="relref">Section 4.7</a> of [<a href="#RFC7517" class="xref">RFC7517</a>]</span> requires that the key in the first certificate of
          the <code>x5c</code> parameter match the public key represented by those
          other members of the JWK.<a href="#section-2.2.2-1" class="pilcrow">¶</a></p>
</section>
</div>
</section>
</div>
</section>
</div>
<div id="CertificateBoundAccessTokens">
<section id="section-3">
      <h2 id="name-mutual-tls-client-certifica">
<a href="#section-3" class="section-number selfRef">3. </a><a href="#name-mutual-tls-client-certifica" class="section-name selfRef">Mutual-TLS Client Certificate-Bound Access Tokens</a>
      </h2>
<p id="section-3-1">
  When mutual TLS is used by the client on the connection to the token endpoint,
  the authorization server is able to bind the issued access token to the client certificate.
  Such a binding is accomplished by associating the certificate with the token in
  a way that can be accessed by the protected resource, such as embedding the certificate
  hash in the issued access token directly, using the syntax described in <a href="#x5t" class="xref">Section 3.1</a>,
  or through token introspection as described in <a href="#introspect" class="xref">Section 3.2</a>.
  Binding the access token to the client certificate in that fashion has the benefit of
  decoupling that binding from the client's authentication with the
  authorization server, which enables mutual TLS during protected resource access to
  serve purely as a proof-of-possession mechanism.
  Other methods of associating a certificate with an access token are possible,
  per agreement by the authorization server and the protected resource, but are
  beyond the scope of this specification.<a href="#section-3-1" class="pilcrow">¶</a></p>
<p id="section-3-2">
  In order for a resource server to use certificate-bound access tokens, it
  must have advance knowledge that mutual TLS is to be used for some or all
  resource accesses.  

   In particular, the access token
   itself cannot be used as input to the decision of whether or not to
   request mutual TLS because (from the TLS perspective) it is
   "Application Data", only exchanged after the TLS handshake has been
   completed, and the initial CertificateRequest occurs during the
   handshake, before the Application Data is available.

   Although subsequent opportunities for a TLS client to
  present a certificate may be available, e.g., via TLS 1.2 renegotiation
  <span>[<a href="#RFC5246" class="xref">RFC5246</a>]</span> or TLS 1.3 post-handshake authentication <span>[<a href="#RFC8446" class="xref">RFC8446</a>]</span>, this document
  makes no provision for their usage.  It is expected to be common that a
  mutual-TLS-using resource server will require mutual TLS for all resources hosted
  thereupon or will serve mutual-TLS-protected and regular resources on separate
  hostname and port combinations, though other workflows are possible. 

How
  resource server policy is synchronized with the authorization server (AS) is out of scope for this
  document.<a href="#section-3-2" class="pilcrow">¶</a></p>
<p id="section-3-3">
  Within the scope of a mutual-TLS-protected resource-access flow,
  the client makes protected resource requests, as described in <span>[<a href="#RFC6750" class="xref">RFC6750</a>]</span>,
  however, those requests <span class="bcp14">MUST</span> be made over a mutually authenticated TLS connection
  using the same certificate that was used for mutual TLS at the token endpoint.<a href="#section-3-3" class="pilcrow">¶</a></p>
<p id="section-3-4">
  The protected resource <span class="bcp14">MUST</span> obtain, from its TLS implementation layer, the client certificate
  used for mutual TLS
  and <span class="bcp14">MUST</span> verify that the certificate matches the
  certificate associated with the access token. If they do not match,
  the resource access attempt <span class="bcp14">MUST</span> be rejected with an error, per <span>[<a href="#RFC6750" class="xref">RFC6750</a>]</span>,
  using an HTTP 401 status code and the <code>invalid_token</code> error code.<a href="#section-3-4" class="pilcrow">¶</a></p>
<p id="section-3-5">
  Metadata to convey server and client capabilities for mutual-TLS client certificate-bound access tokens
  is defined in Sections <a href="#server_metadata_at" class="xref">3.3</a> and <a href="#client_metadata_at" class="xref">3.4</a>, respectively.<a href="#section-3-5" class="pilcrow">¶</a></p>
<div id="x5t">
<section id="section-3.1">
        <h3 id="name-jwt-certificate-thumbprint-">
<a href="#section-3.1" class="section-number selfRef">3.1. </a><a href="#name-jwt-certificate-thumbprint-" class="section-name selfRef">JWT Certificate Thumbprint Confirmation Method</a>
        </h3>
<p id="section-3.1-1">
    When access tokens are represented as JSON Web Tokens (JWT) <span>[<a href="#RFC7519" class="xref">RFC7519</a>]</span>,
    the certificate hash information <span class="bcp14">SHOULD</span> be represented using
    the <code>x5t#S256</code> confirmation method member defined herein.<a href="#section-3.1-1" class="pilcrow">¶</a></p>
<p id="section-3.1-2">
    To represent the hash of a certificate in a JWT, this specification
    defines the new JWT Confirmation Method <span>[<a href="#RFC7800" class="xref">RFC7800</a>]</span> member <code>x5t#S256</code> for the X.509
    Certificate SHA-256 Thumbprint. The value of the <code>x5t#S256</code> member
    is a base64url-encoded <span>[<a href="#RFC4648" class="xref">RFC4648</a>]</span> SHA-256
    <span>[<a href="#SHS" class="xref">SHS</a>]</span> hash (a.k.a., thumbprint, fingerprint,
    or digest) of the DER encoding <span>[<a href="#X690" class="xref">X690</a>]</span> of
    the X.509 certificate <span>[<a href="#RFC5280" class="xref">RFC5280</a>]</span>. The
    base64url-encoded value <span class="bcp14">MUST</span> omit all trailing pad '='
    characters and <span class="bcp14">MUST NOT</span> include any line breaks,
    whitespace, or other additional characters.<a href="#section-3.1-2" class="pilcrow">¶</a></p>
<p id="section-3.1-3">
    The following is an example of a JWT payload containing an <code>x5t#S256</code> certificate thumbprint
    confirmation method. The new JWT content introduced by this specification is the <code>cnf</code>
    confirmation method claim at the bottom of the example that has
    the <code>x5t#S256</code> confirmation method member containing the value that is the hash
    of the client certificate to which the access token is bound.<a href="#section-3.1-3" class="pilcrow">¶</a></p>
<span id="name-example-jwt-claims-set-with"></span><div id="eg_x5ts256jwt">
<figure id="figure-2">
          <div id="section-3.1-4.1">
<pre class="sourcecode lang-json">
  {
    "iss": "https://server.example.com",
    "sub": "ty.webb@example.com",
    "exp": 1493726400,
    "nbf": 1493722800,
    "cnf":{
      "x5t#S256": "bwcK0esc3ACC3DB2Y5_lESsXE8o9ltc05O89jdN-dg2"
    }
  }
</pre>
</div>
<figcaption><a href="#figure-2" class="selfRef">Figure 2</a>:
<a href="#name-example-jwt-claims-set-with" class="selfRef">Example JWT Claims Set with an X.509 Certificate Thumbprint Confirmation Method</a>
          </figcaption></figure>
</div>
</section>
</div>
<div id="introspect">
<section id="section-3.2">
        <h3 id="name-confirmation-method-for-tok">
<a href="#section-3.2" class="section-number selfRef">3.2. </a><a href="#name-confirmation-method-for-tok" class="section-name selfRef">Confirmation Method for Token Introspection</a>
        </h3>
<p id="section-3.2-1">
          OAuth 2.0 Token Introspection <span>[<a href="#RFC7662" class="xref">RFC7662</a>]</span> defines a
          method for a protected resource to query
          an authorization server about the active state of an
          access token as well as to determine metainformation about the token.<a href="#section-3.2-1" class="pilcrow">¶</a></p>
<p id="section-3.2-2">
          For a mutual-TLS client certificate-bound access token, the hash of the
          certificate to which the token is bound
          is conveyed to the protected resource as metainformation
          in a token introspection response. The hash is conveyed using the same
          <code>cnf</code> with <code>x5t#S256</code> member structure as the
          certificate SHA-256 thumbprint confirmation method, described in
          <a href="#x5t" class="xref">Section 3.1</a>, as a top-level member of the introspection response JSON.
          The protected resource compares
          that certificate hash to a hash of the client certificate used for
          mutual-TLS authentication
          and rejects the request if they do not match.<a href="#section-3.2-2" class="pilcrow">¶</a></p>
<p id="section-3.2-3">
          The following is an example of an introspection response for an active token with
          an <code>x5t#S256</code> certificate thumbprint
          confirmation method. The new introspection response content introduced by this specification is the <code>cnf</code>
          confirmation method at the bottom of the example that has
          the <code>x5t#S256</code> confirmation method member containing the value that is the hash
          of the client certificate to which the access token is bound.<a href="#section-3.2-3" class="pilcrow">¶</a></p>
<span id="name-example-introspection-respo"></span><div id="eg_x5ts256intro">
<figure id="figure-3">
          <div class="artwork art-text alignLeft" id="section-3.2-4.1">
<pre>
  HTTP/1.1 200 OK
  Content-Type: application/json

  {
    "active": true,
    "iss": "https://server.example.com",
    "sub": "ty.webb@example.com",
    "exp": 1493726400,
    "nbf": 1493722800,
    "cnf":{
      "x5t#S256": "bwcK0esc3ACC3DB2Y5_lESsXE8o9ltc05O89jdN-dg2"
    }
  }
</pre>
</div>
<figcaption><a href="#figure-3" class="selfRef">Figure 3</a>:
<a href="#name-example-introspection-respo" class="selfRef">Example Introspection Response for a Certificate-Bound Access Token</a>
          </figcaption></figure>
</div>
</section>
</div>
<div id="server_metadata_at">
<section id="section-3.3">
        <h3 id="name-authorization-server-metada">
<a href="#section-3.3" class="section-number selfRef">3.3. </a><a href="#name-authorization-server-metada" class="section-name selfRef">Authorization Server Metadata</a>
        </h3>
<p id="section-3.3-1">This document introduces the following new authorization server
            metadata <span>[<a href="#RFC8414" class="xref">RFC8414</a>]</span> parameter to signal the server's capability to issue certificate-bound access tokens:<a href="#section-3.3-1" class="pilcrow">¶</a></p>
<dl class="dlNewline" id="section-3.3-2">
          <dt id="section-3.3-2.1">tls_client_certificate_bound_access_tokens</dt>
<dd id="section-3.3-2.2">
            <span class="bcp14">OPTIONAL</span>. Boolean value indicating server support for
                mutual-TLS client certificate-bound access tokens. If omitted, the
                default value is <code>false</code>.<a href="#section-3.3-2.2" class="pilcrow">¶</a>
</dd>
</dl>
</section>
</div>
<div id="client_metadata_at">
<section id="section-3.4">
        <h3 id="name-client-registration-metadata-2">
<a href="#section-3.4" class="section-number selfRef">3.4. </a><a href="#name-client-registration-metadata-2" class="section-name selfRef">Client Registration Metadata</a>
        </h3>
<p id="section-3.4-1">The following new client
          metadata parameter is introduced to convey the client's intention to use certificate-bound access tokens:<a href="#section-3.4-1" class="pilcrow">¶</a></p>
<dl class="dlNewline" id="section-3.4-2">
          <dt id="section-3.4-2.1">tls_client_certificate_bound_access_tokens</dt>
<dd id="section-3.4-2.2">
            <span class="bcp14">OPTIONAL</span>. Boolean value used to indicate the client's intention
              to use mutual-TLS client certificate-bound access tokens.
              If omitted, the default value is <code>false</code>.<a href="#section-3.4-2.2" class="pilcrow">¶</a>
</dd>
</dl>
<p id="section-3.4-3">

          Note that if a client that has indicated the intention to use mutual-TLS client certificate-bound tokens
          makes a request to the token endpoint over a non-mutual-TLS connection,
          it is at the authorization server's discretion as to whether to return an error or issue an unbound token.<a href="#section-3.4-3" class="pilcrow">¶</a></p>
</section>
</div>
</section>
</div>
<div id="PubClient">
<section id="section-4">
      <h2 id="name-public-clients-and-certific">
<a href="#section-4" class="section-number selfRef">4. </a><a href="#name-public-clients-and-certific" class="section-name selfRef">Public Clients and Certificate-Bound Tokens</a>
      </h2>
<p id="section-4-1">
        Mutual-TLS OAuth client authentication and certificate-bound access tokens
        can be used independently of each other.
        Use of certificate-bound access tokens without mutual-TLS OAuth client authentication, for example,
        is possible in support of binding access tokens to a TLS client certificate for public clients (those without
        authentication credentials associated with the <code>client_id</code>).
        The authorization server would configure the TLS stack in the same manner as for the Self-Signed Certificate method
        such that it does not verify that the certificate presented by the client during the handshake is
        signed by a trusted CA. Individual instances of a client would create a self-signed
        certificate for mutual TLS with both the authorization server and resource server. The authorization
        server would not use the mutual-TLS certificate to authenticate the client at the OAuth layer
        but would bind the issued access token
        to the certificate for which the client has proven possession of the corresponding private key.
        The access token is then bound to the certificate and can only be used by the client
        possessing the certificate and corresponding private key and utilizing them to negotiate mutual TLS on
        connections to the resource server.
        When the authorization server issues a refresh token to such a client, it <span class="bcp14">SHOULD</span> also bind the refresh token
        to the respective certificate and check the binding when the refresh token is presented to get new
        access tokens.
        The implementation details of the binding of the refresh token are at the discretion of the authorization
        server.<a href="#section-4-1" class="pilcrow">¶</a></p>
</section>
</div>
<div id="endpointAliases">
<section id="section-5">
      <h2 id="name-metadata-for-mutual-tls-end">
<a href="#section-5" class="section-number selfRef">5. </a><a href="#name-metadata-for-mutual-tls-end" class="section-name selfRef">Metadata for Mutual-TLS Endpoint Aliases</a>
      </h2>
<p id="section-5-1">
        The process of negotiating client certificate-based mutual TLS involves a TLS server requesting a certificate
        from the TLS client (the client does not provide one unsolicited). Although a server can be configured
        such that client certificates are optional, meaning that the connection is allowed to continue when the client
        does not provide a certificate, the act of a server requesting a certificate can result in undesirable
        behavior from some clients. This is particularly true of web browsers as TLS clients, which will typically
        present the end user with an intrusive certificate selection interface when the server requests a certificate.<a href="#section-5-1" class="pilcrow">¶</a></p>
<p id="section-5-2">
        Authorization servers supporting both clients using mutual TLS and conventional clients <span class="bcp14">MAY</span> chose to
        isolate the server side mutual-TLS behavior to only clients intending to do mutual TLS, thus
        avoiding any undesirable effects it might have on conventional clients. The following authorization server
        metadata parameter is introduced to facilitate such separation:<a href="#section-5-2" class="pilcrow">¶</a></p>
<dl class="dlNewline" id="section-5-3">
        <dt id="section-5-3.1">mtls_endpoint_aliases</dt>
<dd id="section-5-3.2">
          <span class="bcp14">OPTIONAL</span>.
            A JSON object containing alternative authorization server endpoints that,
            when present, an OAuth client intending to do mutual TLS
            uses in preference to the conventional endpoints.
            The parameter value itself consists of one or more endpoint parameters,
            such as <code>token_endpoint</code>,
            <code>revocation_endpoint</code>,
            <code>introspection_endpoint</code>, etc., conventionally defined for the
            top level of authorization server metadata.
            An OAuth client intending to do mutual TLS
            (for OAuth client authentication and/or to acquire or use certificate-bound tokens)
            when making a request directly to the authorization server <span class="bcp14">MUST</span>
            use the alias URL of the endpoint within the <code>mtls_endpoint_aliases</code>, when present,
            in preference to the endpoint URL of the same name at the top level of metadata.
            When an endpoint is not present in
            <code>mtls_endpoint_aliases</code>, then the client uses the conventional endpoint URL
            defined at the top level of the authorization server metadata. Metadata parameters within
            <code>mtls_endpoint_aliases</code> that do not define
            endpoints to which an OAuth client makes a direct request have no meaning and <span class="bcp14">SHOULD</span> be ignored.<a href="#section-5-3.2" class="pilcrow">¶</a>
</dd>
</dl>
<p id="section-5-4">
        Below is an example of an authorization server metadata document with the
        <code>mtls_endpoint_aliases</code> parameter, which indicates aliases for the
        token, revocation, and introspection endpoints that an OAuth client intending to do mutual TLS
        would use in preference to the conventional token, revocation, and
 introspection endpoints.
        Note that the endpoints in <code>mtls_endpoint_aliases</code> use a different
        host than their conventional counterparts, which allows the authorization server
        (via TLS <code>server_name</code> extension <span>[<a href="#RFC6066" class="xref">RFC6066</a>]</span> or actual distinct hosts) to differentiate its TLS behavior as appropriate.<a href="#section-5-4" class="pilcrow">¶</a></p>
<span id="name-example-authorization-serve"></span><div id="as-meta">
<figure id="figure-4">
        <div id="section-5-5.1">
<pre class="sourcecode lang-json">
{
  "issuer": "https://server.example.com",
  "authorization_endpoint": "https://server.example.com/authz",
  "token_endpoint": "https://server.example.com/token",
  "introspection_endpoint": "https://server.example.com/introspect",
  "revocation_endpoint": "https://server.example.com/revo",
  "jwks_uri": "https://server.example.com/jwks",
  "response_types_supported": ["code"],
  "response_modes_supported": ["fragment","query","form_post"],
  "grant_types_supported": ["authorization_code", "refresh_token"],
  "token_endpoint_auth_methods_supported":
                  ["tls_client_auth","client_secret_basic","none"],
  "tls_client_certificate_bound_access_tokens": true,
  "mtls_endpoint_aliases": {
    "token_endpoint": "https://mtls.example.com/token",
    "revocation_endpoint": "https://mtls.example.com/revo",
    "introspection_endpoint": "https://mtls.example.com/introspect"
  }
}
</pre>
</div>
<figcaption><a href="#figure-4" class="selfRef">Figure 4</a>:
<a href="#name-example-authorization-serve" class="selfRef">Example Authorization Server Metadata with Mutual-TLS Endpoint Aliases</a>
        </figcaption></figure>
</div>
</section>
</div>
<div id="Impl">
<section id="section-6">
      <h2 id="name-implementation-consideratio">
<a href="#section-6" class="section-number selfRef">6. </a><a href="#name-implementation-consideratio" class="section-name selfRef">Implementation Considerations</a>
      </h2>
<div id="ImplAS">
<section id="section-6.1">
        <h3 id="name-authorization-server">
<a href="#section-6.1" class="section-number selfRef">6.1. </a><a href="#name-authorization-server" class="section-name selfRef">Authorization Server</a>
        </h3>
<p id="section-6.1-1">The authorization server needs to set up its TLS configuration appropriately
    for the OAuth client authentication methods it supports.<a href="#section-6.1-1" class="pilcrow">¶</a></p>
<p id="section-6.1-2">An authorization server that supports mutual-TLS client authentication
    and other client authentication methods or public clients in parallel would make mutual TLS
    optional (i.e., allowing a handshake to continue after the server requests a client certificate
    but the client does not send one).<a href="#section-6.1-2" class="pilcrow">¶</a></p>
<p id="section-6.1-3">In order to support the Self-Signed Certificate method alone, the authorization server
    would configure the TLS stack in such a way that it does not verify whether the
    certificate presented by the client during the handshake is signed by a trusted CA 
    certificate.<a href="#section-6.1-3" class="pilcrow">¶</a></p>
<p id="section-6.1-4">As described in <a href="#CertificateBoundAccessTokens" class="xref">Section 3</a>, the authorization server
    binds the issued access token to the TLS client certificate, which means that it
    will only issue certificate-bound tokens for a
    certificate that the client has proven possession of the corresponding private key.<a href="#section-6.1-4" class="pilcrow">¶</a></p>
<p id="section-6.1-5">The authorization server may also consider hosting the token endpoint
    and other endpoints requiring client authentication on
    a separate host name or port in order to prevent unintended impact on the TLS behavior of
    its other endpoints, e.g., the authorization endpoint. As described in <a href="#endpointAliases" class="xref">Section 5</a>,
    it may further isolate any potential impact of the server requesting client certificates by
    offering a distinct set of endpoints on a separate host or port, which are aliases for
    the originals that a client intending to do mutual TLS will use in preference to the conventional endpoints.<a href="#section-6.1-5" class="pilcrow">¶</a></p>
</section>
</div>
<div id="ImplRS">
<section id="section-6.2">
        <h3 id="name-resource-server">
<a href="#section-6.2" class="section-number selfRef">6.2. </a><a href="#name-resource-server" class="section-name selfRef">Resource Server</a>
        </h3>
<p id="section-6.2-1">
      OAuth divides the roles and responsibilities such that the resource server relies
      on the authorization server to perform client authentication and obtain resource-owner (end-user)
      authorization. The resource server makes authorization decisions based on the access token
      presented by the client but does not directly authenticate the client per se.
      The manner in which an access token is bound to the client certificate and how a protected resource verifies the proof-of-possession
      decouples that from the specific method that the client used to authenticate with the
      authorization server. Mutual TLS during protected resource access can, therefore,
      serve purely as a proof-of-possession mechanism.
      As such, it is not necessary for the resource server to validate
      the trust chain of the client's certificate in any of the methods
      defined in this document.
      The resource server would, therefore, configure the TLS stack
      in a way that it does not verify whether the certificate presented by the client
      during the handshake is signed by a trusted CA certificate.<a href="#section-6.2-1" class="pilcrow">¶</a></p>
</section>
</div>
<div id="ImplExp">
<section id="section-6.3">
        <h3 id="name-certificate-expiration-and-">
<a href="#section-6.3" class="section-number selfRef">6.3. </a><a href="#name-certificate-expiration-and-" class="section-name selfRef">Certificate Expiration and Bound Access Tokens</a>
        </h3>
<p id="section-6.3-1">
        As described in <a href="#CertificateBoundAccessTokens" class="xref">Section 3</a>,
        an access token is bound to a specific client certificate, which means that
        the same certificate must be used for mutual TLS on protected resource access.
        It also implies that access tokens are invalidated when a client updates the certificate,
        which can be handled similarly to expired access tokens where the client
        requests a new access token (typically with a refresh token) and retries the protected resource
        request.<a href="#section-6.3-1" class="pilcrow">¶</a></p>
</section>
</div>
<div id="ImplImplicit">
<section id="section-6.4">
        <h3 id="name-implicit-grant-unsupported">
<a href="#section-6.4" class="section-number selfRef">6.4. </a><a href="#name-implicit-grant-unsupported" class="section-name selfRef">Implicit Grant Unsupported</a>
        </h3>
<p id="section-6.4-1">
      This document describes binding an access token to the
      client certificate presented on the TLS connection from the client to the
      authorization server's token endpoint,
      however, such binding of access tokens issued directly from the authorization
      endpoint via the implicit grant flow is explicitly out of scope.
      End users interact directly with the authorization endpoint using a web browser,
      and the use of client certificates in user's browsers bring operational and
      usability issues that make it undesirable to support certificate-bound access
      tokens issued in the implicit grant flow. Implementations wanting to employ
      certificate-bound access tokens should utilize grant types
      that involve the client making an access token request directly to the token endpoint
      (e.g., the authorization code and refresh token grant types).<a href="#section-6.4-1" class="pilcrow">¶</a></p>
</section>
</div>
<div id="TTRP">
<section id="section-6.5">
        <h3 id="name-tls-termination">
<a href="#section-6.5" class="section-number selfRef">6.5. </a><a href="#name-tls-termination" class="section-name selfRef">TLS Termination</a>
        </h3>
<p id="section-6.5-1">
      An authorization server or resource server <span class="bcp14">MAY</span> choose to terminate TLS connections at a load balancer,
      reverse proxy, or other network intermediary. How the client certificate metadata is securely
      communicated between the intermediary and the application server, in this case, is out of scope of this specification.<a href="#section-6.5-1" class="pilcrow">¶</a></p>
</section>
</div>
</section>
</div>
<div id="Security">
<section id="section-7">
      <h2 id="name-security-considerations">
<a href="#section-7" class="section-number selfRef">7. </a><a href="#name-security-considerations" class="section-name selfRef">Security Considerations</a>
      </h2>
<section id="section-7.1">
        <h3 id="name-certificate-bound-refresh-t">
<a href="#section-7.1" class="section-number selfRef">7.1. </a><a href="#name-certificate-bound-refresh-t" class="section-name selfRef">Certificate-Bound Refresh Tokens</a>
        </h3>
<p id="section-7.1-1">The OAuth 2.0 Authorization Framework <span>[<a href="#RFC6749" class="xref">RFC6749</a>]</span> requires that an authorization server (AS)
          bind refresh tokens to the client to which they were issued and that confidential clients
          (those having established authentication credentials with the AS) authenticate to
          the AS when presenting a refresh token. As a result, refresh tokens are indirectly certificate-bound by way of the
          client ID and the associated requirement for (certificate-based) authentication to the AS when
          issued to clients utilizing the <code>tls_client_auth</code> or
          <code>self_signed_tls_client_auth</code> methods of client authentication.
          <a href="#PubClient" class="xref">Section 4</a> describes certificate-bound refresh tokens issued to public clients (those without
          authentication credentials associated with the <code>client_id</code>).<a href="#section-7.1-1" class="pilcrow">¶</a></p>
</section>
<section id="section-7.2">
        <h3 id="name-certificate-thumbprint-bind">
<a href="#section-7.2" class="section-number selfRef">7.2. </a><a href="#name-certificate-thumbprint-bind" class="section-name selfRef">Certificate Thumbprint Binding</a>
        </h3>
<p id="section-7.2-1">
          The binding between the certificate and access token specified in <a href="#x5t" class="xref">Section 3.1</a> uses
          a cryptographic hash of the certificate. It relies on the hash function having sufficient
          second-preimage resistance so as to make it computationally infeasible to
          find or create another certificate that produces to the same hash output value.
          The SHA-256 hash function was used because it meets the aforementioned requirement while being widely available.
          If, in the future, certificate thumbprints need to be computed using
          hash function(s) other than SHA-256, it is suggested that, for additional
          related JWT confirmation methods, members be defined for that purpose
          and registered in the IANA "JWT Confirmation Methods" registry
          <span>[<a href="#IANA.JWT.Claims" class="xref">IANA.JWT.Claims</a>]</span>
          for JWT <code>cnf</code> member values.<a href="#section-7.2-1" class="pilcrow">¶</a></p>
<p id="section-7.2-2">
          Community knowledge about the strength of various algorithms and
          feasible attacks can change suddenly, and experience shows that a
          document about security is a point-in-time
          statement. Readers are advised to seek out any errata or updates
          that apply to this document.<a href="#section-7.2-2" class="pilcrow">¶</a></p>
</section>
<div id="TLSV">
<section id="section-7.3">
        <h3 id="name-tls-versions-and-best-pract">
<a href="#section-7.3" class="section-number selfRef">7.3. </a><a href="#name-tls-versions-and-best-pract" class="section-name selfRef">TLS Versions and Best Practices</a>
        </h3>
<p id="section-7.3-1">
          This document is applicable with any TLS version supporting certificate-based client authentication.
          Both <span><a href="#RFC8446" class="xref">TLS 1.3</a> [<a href="#RFC8446" class="xref">RFC8446</a>]</span> and <span><a href="#RFC5246" class="xref">TLS 1.2</a> [<a href="#RFC5246" class="xref">RFC5246</a>]</span> are cited herein, because,
          at the time of writing, 1.3 is the newest version, while 1.2 is the most widely deployed.
          General implementation and security considerations for TLS, including version recommendations,
          can be found in <span>[<a href="#BCP195" class="xref">BCP195</a>]</span>.<a href="#section-7.3-1" class="pilcrow">¶</a></p>
<p id="section-7.3-2">
          TLS certificate validation
          (for both client and server certificates) requires a local database of
          trusted certificate authorities (CAs). Decisions about what CAs to trust
          and how to make such a determination of trust are out of scope for this
          document.<a href="#section-7.3-2" class="pilcrow">¶</a></p>
</section>
</div>
<div id="certspoofing">
<section id="section-7.4">
        <h3 id="name-x509-certificate-spoofing">
<a href="#section-7.4" class="section-number selfRef">7.4. </a><a href="#name-x509-certificate-spoofing" class="section-name selfRef">X.509 Certificate Spoofing</a>
        </h3>
<p id="section-7.4-1">
          If the PKI method of client authentication is used, an attacker could try to impersonate a client using
          a certificate with the same subject (DN or SAN) but issued by a
   different CA that the authorization server trusts.
          To cope with that threat, the authorization server <span class="bcp14">SHOULD</span> only accept, as trust anchors,
          a limited number of CAs whose certificate issuance policy meets its security requirements.
          There is an assumption then that the client and server agree out of band on the set
          of trust anchors that the server uses to create and validate the
          certificate chain. Without this assumption the use of a subject
          to identify the client certificate would open the server up to
          certificate spoofing attacks.<a href="#section-7.4-1" class="pilcrow">¶</a></p>
</section>
</div>
<section id="section-7.5">
        <h3 id="name-x509-certificate-parsing-an">
<a href="#section-7.5" class="section-number selfRef">7.5. </a><a href="#name-x509-certificate-parsing-an" class="section-name selfRef">X.509 Certificate Parsing and Validation Complexity</a>
        </h3>
<p id="section-7.5-1">
          Parsing and validation of X.509 certificates and certificate chains
   is complex, and implementation
          mistakes have previously exposed security vulnerabilities.
          Complexities of validation include (but are not limited to)
          <span>[<a href="#CX5P" class="xref">CX5P</a>]</span> <span>[<a href="#DCW" class="xref">DCW</a>]</span> <span>[<a href="#RFC5280" class="xref">RFC5280</a>]</span>:<a href="#section-7.5-1" class="pilcrow">¶</a></p>
<ul>
<li id="section-7.5-2.1">checking of basic constraints, basic and extended key usage constraints, validity periods, and critical extensions;<a href="#section-7.5-2.1" class="pilcrow">¶</a>
</li>
<li id="section-7.5-2.2">handling of embedded NUL bytes in ASN.1 counted-length strings and non-canonical or non-normalized string representations in subject names;<a href="#section-7.5-2.2" class="pilcrow">¶</a>
</li>
<li id="section-7.5-2.3">handling of wildcard patterns in subject names;<a href="#section-7.5-2.3" class="pilcrow">¶</a>
</li>
<li id="section-7.5-2.4">recursive verification of certificate chains and checking certificate revocation.<a href="#section-7.5-2.4" class="pilcrow">¶</a>
</li>
</ul>
<p id="section-7.5-3">
          For these reasons, implementors <span class="bcp14">SHOULD</span> use an established and well-tested X.509 library
          (such as one used by an established TLS library) for validation of X.509 certificate chains
          and <span class="bcp14">SHOULD NOT</span> attempt to write their own X.509 certificate validation procedures.<a href="#section-7.5-3" class="pilcrow">¶</a></p>
</section>
</section>
</div>
<div id="Privacy">
<section id="section-8">
      <h2 id="name-privacy-considerations">
<a href="#section-8" class="section-number selfRef">8. </a><a href="#name-privacy-considerations" class="section-name selfRef">Privacy Considerations</a>
      </h2>
<p id="section-8-1">
        In TLS versions prior to 1.3, the client's certificate is sent unencrypted in the initial handshake and
        can potentially be used by third parties to monitor, track, and correlate client activity.
        This is likely of little concern for clients that act on behalf of a
 significant number of end users because
        individual user activity will not be discernible amidst the client activity as a whole.
        However, clients that act on behalf of a single end user, such as a native application on a mobile device,
        should use TLS version 1.3 whenever possible or consider the potential privacy implications of using mutual TLS on
        earlier versions.<a href="#section-8-1" class="pilcrow">¶</a></p>
</section>
</div>
<div id="IANA">
<section id="section-9">
      <h2 id="name-iana-considerations">
<a href="#section-9" class="section-number selfRef">9. </a><a href="#name-iana-considerations" class="section-name selfRef">IANA Considerations</a>
      </h2>
<section id="section-9.1">
        <h3 id="name-jwt-confirmation-methods-re">
<a href="#section-9.1" class="section-number selfRef">9.1. </a><a href="#name-jwt-confirmation-methods-re" class="section-name selfRef">JWT Confirmation Methods Registration</a>
        </h3>
<p id="section-9.1-1">
          Per this specification, the following value has been registered
          in the IANA "JWT Confirmation Methods" registry
          <span>[<a href="#IANA.JWT.Claims" class="xref">IANA.JWT.Claims</a>]</span>
          for JWT <code>cnf</code> member values
          established by <span>[<a href="#RFC7800" class="xref">RFC7800</a>]</span>.<a href="#section-9.1-1" class="pilcrow">¶</a></p>
<dl class="dlParallel dlCompact" id="section-9.1-2">
          <dt id="section-9.1-2.1">Confirmation Method Value:</dt>
<dd id="section-9.1-2.2">
            <code>x5t#S256</code><a href="#section-9.1-2.2" class="pilcrow">¶</a>
</dd>
<dt id="section-9.1-2.3">Confirmation Method Description:</dt>
<dd id="section-9.1-2.4">X.509 Certificate SHA-256 Thumbprint<a href="#section-9.1-2.4" class="pilcrow">¶</a>
</dd>
<dt id="section-9.1-2.5">Change Controller:</dt>
<dd id="section-9.1-2.6">IESG<a href="#section-9.1-2.6" class="pilcrow">¶</a>
</dd>
<dt id="section-9.1-2.7">Specification Document(s):</dt>
<dd id="section-9.1-2.8">
            <a href="#x5t" class="xref">Section 3.1</a>
   of RFC 8705<a href="#section-9.1-2.8" class="pilcrow">¶</a>
</dd>
</dl>
</section>
<section id="section-9.2">
        <h3 id="name-authorization-server-metadat">
<a href="#section-9.2" class="section-number selfRef">9.2. </a><a href="#name-authorization-server-metadat" class="section-name selfRef">Authorization Server Metadata Registration</a>
        </h3>
<p id="section-9.2-1">
          Per this specification, the following values have been registered 
          in the IANA "OAuth Authorization Server Metadata" registry
          <span>[<a href="#IANA.OAuth.Parameters" class="xref">IANA.OAuth.Parameters</a>]</span> established by <span>[<a href="#RFC8414" class="xref">RFC8414</a>]</span>.<a href="#section-9.2-1" class="pilcrow">¶</a></p>
<dl class="dlParallel dlCompact" id="section-9.2-2">
          <dt id="section-9.2-2.1">Metadata Name:</dt>
<dd id="section-9.2-2.2">
            <code>tls_client_certificate_bound_access_tokens</code><a href="#section-9.2-2.2" class="pilcrow">¶</a>
</dd>
<dt id="section-9.2-2.3">Metadata Description:</dt>
<dd id="section-9.2-2.4">Indicates authorization server
          support for mutual-TLS client certificate-bound access tokens.<a href="#section-9.2-2.4" class="pilcrow">¶</a>
</dd>
<dt id="section-9.2-2.5">Change Controller:</dt>
<dd id="section-9.2-2.6">IESG<a href="#section-9.2-2.6" class="pilcrow">¶</a>
</dd>
<dt id="section-9.2-2.7">Specification Document(s):</dt>
<dd id="section-9.2-2.8">
            <a href="#server_metadata_at" class="xref">Section 3.3</a> of RFC 8705<a href="#section-9.2-2.8" class="pilcrow">¶</a>
</dd>
</dl>
<dl class="dlParallel dlCompact" id="section-9.2-3">
          <dt id="section-9.2-3.1">Metadata Name:</dt>
<dd id="section-9.2-3.2">
            <code>mtls_endpoint_aliases</code><a href="#section-9.2-3.2" class="pilcrow">¶</a>
</dd>
<dt id="section-9.2-3.3">Metadata Description:</dt>
<dd id="section-9.2-3.4">JSON object containing alternative
   authorization server endpoints, which a client
              intending to do mutual TLS will use in preference to the conventional endpoints.<a href="#section-9.2-3.4" class="pilcrow">¶</a>
</dd>
<dt id="section-9.2-3.5">Change Controller:</dt>
<dd id="section-9.2-3.6">IESG<a href="#section-9.2-3.6" class="pilcrow">¶</a>
</dd>
<dt id="section-9.2-3.7">Specification Document(s):</dt>
<dd id="section-9.2-3.8">
            <a href="#endpointAliases" class="xref">Section 5</a> of RFC 8705<a href="#section-9.2-3.8" class="pilcrow">¶</a>
</dd>
</dl>
</section>
<section id="section-9.3">
        <h3 id="name-token-endpoint-authenticati">
<a href="#section-9.3" class="section-number selfRef">9.3. </a><a href="#name-token-endpoint-authenticati" class="section-name selfRef">Token Endpoint Authentication Method Registration</a>
        </h3>
<p id="section-9.3-1">
   Per this specification, the following values have been registered 
          in the IANA "OAuth Token Endpoint Authentication Methods" registry
          <span>[<a href="#IANA.OAuth.Parameters" class="xref">IANA.OAuth.Parameters</a>]</span> established by <span>[<a href="#RFC7591" class="xref">RFC7591</a>]</span>.<a href="#section-9.3-1" class="pilcrow">¶</a></p>
<dl class="dlParallel dlCompact" id="section-9.3-2">
          <dt id="section-9.3-2.1">Token Endpoint Authentication Method Name:</dt>
<dd id="section-9.3-2.2">
            <code>tls_client_auth</code><a href="#section-9.3-2.2" class="pilcrow">¶</a>
</dd>
<dt id="section-9.3-2.3">Change Controller:</dt>
<dd id="section-9.3-2.4">IESG<a href="#section-9.3-2.4" class="pilcrow">¶</a>
</dd>
<dt id="section-9.3-2.5">Specification Document(s):</dt>
<dd id="section-9.3-2.6">
            <a href="#metadata_auth_value_pki" class="xref">Section 2.1.1</a> of RFC 8705<a href="#section-9.3-2.6" class="pilcrow">¶</a>
</dd>
</dl>
<dl class="dlParallel dlCompact" id="section-9.3-3">
          <dt id="section-9.3-3.1">Token Endpoint Authentication Method Name:<br>
</dt>
<dd id="section-9.3-3.2">
            <code>self_signed_tls_client_auth</code><a href="#section-9.3-3.2" class="pilcrow">¶</a>
</dd>
<dt id="section-9.3-3.3">Change Controller:</dt>
<dd id="section-9.3-3.4">IESG<a href="#section-9.3-3.4" class="pilcrow">¶</a>
</dd>
<dt id="section-9.3-3.5">Specification Document(s):</dt>
<dd id="section-9.3-3.6">
            <a href="#metadata_auth_value_self_signed" class="xref">Section 2.2.1</a> of RFC 8705<a href="#section-9.3-3.6" class="pilcrow">¶</a>
</dd>
</dl>
</section>
<section id="section-9.4">
        <h3 id="name-token-introspection-respons">
<a href="#section-9.4" class="section-number selfRef">9.4. </a><a href="#name-token-introspection-respons" class="section-name selfRef">Token Introspection Response Registration</a>
        </h3>
<p id="section-9.4-1">
          "Proof-of-Possession Key Semantics for JSON Web Tokens (JWTs)" <span>[<a href="#RFC7800" class="xref">RFC7800</a>]</span> defined the
          <code>cnf</code> (confirmation) claim that enables
          confirmation key information to be carried in a JWT.
          However, the same proof-of-possession semantics are also useful for introspected access tokens
          whereby the protected resource obtains the confirmation key data as metainformation
          of a token introspection response and uses that information in verifying proof-of-possession.
          Therefore, this specification defines and registers proof-of-possession semantics for
          OAuth 2.0 Token Introspection <span>[<a href="#RFC7662" class="xref">RFC7662</a>]</span> using the <code>cnf</code>
          structure.
          When included as a top-level member of an OAuth token introspection response, <code>cnf</code>
          has the same semantics and format as the claim of the same name defined in <span>[<a href="#RFC7800" class="xref">RFC7800</a>]</span>.
          While this specification only explicitly uses the <code>x5t#S256</code>
          confirmation method member (see <a href="#introspect" class="xref">Section 3.2</a>), it needs to define and register
          the higher-level <code>cnf</code>
          structure as an introspection response member in order to define and use the more specific
          certificate thumbprint confirmation method.<a href="#section-9.4-1" class="pilcrow">¶</a></p>
<p id="section-9.4-2">
          As such, the following values have been registered 
          in the IANA "OAuth Token Introspection Response" registry
          <span>[<a href="#IANA.OAuth.Parameters" class="xref">IANA.OAuth.Parameters</a>]</span>
          established by <span>[<a href="#RFC7662" class="xref">RFC7662</a>]</span>.<a href="#section-9.4-2" class="pilcrow">¶</a></p>
<dl class="dlParallel dlCompact" id="section-9.4-3">
          <dt id="section-9.4-3.1">Claim Name:</dt>
<dd id="section-9.4-3.2">
            <code>cnf</code><a href="#section-9.4-3.2" class="pilcrow">¶</a>
</dd>
<dt id="section-9.4-3.3">Claim Description:</dt>
<dd id="section-9.4-3.4">Confirmation<a href="#section-9.4-3.4" class="pilcrow">¶</a>
</dd>
<dt id="section-9.4-3.5">Change Controller:</dt>
<dd id="section-9.4-3.6">IESG<a href="#section-9.4-3.6" class="pilcrow">¶</a>
</dd>
<dt id="section-9.4-3.7">Specification Document(s):</dt>
<dd id="section-9.4-3.8">
            <span>[<a href="#RFC7800" class="xref">RFC7800</a>]</span> and RFC 8705<a href="#section-9.4-3.8" class="pilcrow">¶</a>
</dd>
</dl>
</section>
<section id="section-9.5">
        <h3 id="name-dynamic-client-registration">
<a href="#section-9.5" class="section-number selfRef">9.5. </a><a href="#name-dynamic-client-registration" class="section-name selfRef">Dynamic Client Registration Metadata Registration</a>
        </h3>
<p id="section-9.5-1">
   Per this specification, the following client metadata definitions
          have been registered in the IANA "OAuth Dynamic Client Registration Metadata" registry
          <span>[<a href="#IANA.OAuth.Parameters" class="xref">IANA.OAuth.Parameters</a>]</span>
          established by <span>[<a href="#RFC7591" class="xref">RFC7591</a>]</span>:<a href="#section-9.5-1" class="pilcrow">¶</a></p>
<dl class="dlParallel dlCompact" id="section-9.5-2">
          <dt id="section-9.5-2.1">
              Client Metadata Name:</dt>
<dd id="section-9.5-2.2">
            <code>tls_client_certificate_bound_access_tokens</code><a href="#section-9.5-2.2" class="pilcrow">¶</a>
</dd>
<dt id="section-9.5-2.3">
              Client Metadata Description:</dt>
<dd id="section-9.5-2.4">Indicates the client's
              intention to use mutual-TLS client certificate-bound access
              tokens.<a href="#section-9.5-2.4" class="pilcrow">¶</a>
</dd>
<dt id="section-9.5-2.5">
              Change Controller:</dt>
<dd id="section-9.5-2.6">IESG<a href="#section-9.5-2.6" class="pilcrow">¶</a>
</dd>
<dt id="section-9.5-2.7">
              Specification Document(s):</dt>
<dd id="section-9.5-2.8">
            <a href="#client_metadata_at" class="xref">Section 3.4</a> of RFC 8705<a href="#section-9.5-2.8" class="pilcrow">¶</a>
</dd>
</dl>
<dl class="dlParallel dlCompact" id="section-9.5-3">
          <dt id="section-9.5-3.1">
              Client Metadata Name:</dt>
<dd id="section-9.5-3.2">
            <code>tls_client_auth_subject_dn</code><a href="#section-9.5-3.2" class="pilcrow">¶</a>
</dd>
<dt id="section-9.5-3.3">
              Client Metadata Description:</dt>
<dd id="section-9.5-3.4">String value specifying
              the expected subject DN of the client certificate.<a href="#section-9.5-3.4" class="pilcrow">¶</a>
</dd>
<dt id="section-9.5-3.5">
              Change Controller:</dt>
<dd id="section-9.5-3.6">IESG<a href="#section-9.5-3.6" class="pilcrow">¶</a>
</dd>
<dt id="section-9.5-3.7">
              Specification Document(s):</dt>
<dd id="section-9.5-3.8">
            <a href="#client_metadata_pki" class="xref">Section 2.1.2</a> of RFC 8705<a href="#section-9.5-3.8" class="pilcrow">¶</a>
</dd>
</dl>
<dl class="dlParallel dlCompact" id="section-9.5-4">
          <dt id="section-9.5-4.1">
              Client Metadata Name:</dt>
<dd id="section-9.5-4.2">
            <code>tls_client_auth_san_dns</code><a href="#section-9.5-4.2" class="pilcrow">¶</a>
</dd>
<dt id="section-9.5-4.3">
              Client Metadata Description:</dt>
<dd id="section-9.5-4.4">String value specifying
              the expected dNSName SAN entry in the client certificate.<a href="#section-9.5-4.4" class="pilcrow">¶</a>
</dd>
<dt id="section-9.5-4.5">
              Change Controller:</dt>
<dd id="section-9.5-4.6">IESG<a href="#section-9.5-4.6" class="pilcrow">¶</a>
</dd>
<dt id="section-9.5-4.7">
              Specification Document(s):</dt>
<dd id="section-9.5-4.8">
            <a href="#client_metadata_pki" class="xref">Section 2.1.2</a> of RFC 8705<a href="#section-9.5-4.8" class="pilcrow">¶</a>
</dd>
</dl>
<dl class="dlParallel dlCompact" id="section-9.5-5">
          <dt id="section-9.5-5.1">
              Client Metadata Name:</dt>
<dd id="section-9.5-5.2">
            <code>tls_client_auth_san_uri</code><a href="#section-9.5-5.2" class="pilcrow">¶</a>
</dd>
<dt id="section-9.5-5.3">
              Client Metadata Description:</dt>
<dd id="section-9.5-5.4">String value specifying
              the expected uniformResourceIdentifier SAN entry in the client
              certificate.<a href="#section-9.5-5.4" class="pilcrow">¶</a>
</dd>
<dt id="section-9.5-5.5">
              Change Controller:</dt>
<dd id="section-9.5-5.6">IESG<a href="#section-9.5-5.6" class="pilcrow">¶</a>
</dd>
<dt id="section-9.5-5.7">
              Specification Document(s):</dt>
<dd id="section-9.5-5.8">
            <a href="#client_metadata_pki" class="xref">Section 2.1.2</a> of RFC 8705<a href="#section-9.5-5.8" class="pilcrow">¶</a>
</dd>
</dl>
<dl class="dlParallel dlCompact" id="section-9.5-6">
          <dt id="section-9.5-6.1">
              Client Metadata Name:</dt>
<dd id="section-9.5-6.2">
            <code>tls_client_auth_san_ip</code><a href="#section-9.5-6.2" class="pilcrow">¶</a>
</dd>
<dt id="section-9.5-6.3">
              Client Metadata Description:</dt>
<dd id="section-9.5-6.4">String value specifying
              the expected iPAddress SAN entry in the client certificate.<a href="#section-9.5-6.4" class="pilcrow">¶</a>
</dd>
<dt id="section-9.5-6.5">
              Change Controller:</dt>
<dd id="section-9.5-6.6">IESG<a href="#section-9.5-6.6" class="pilcrow">¶</a>
</dd>
<dt id="section-9.5-6.7">
              Specification Document(s):</dt>
<dd id="section-9.5-6.8">
            <a href="#client_metadata_pki" class="xref">Section 2.1.2</a> of RFC 8705<a href="#section-9.5-6.8" class="pilcrow">¶</a>
</dd>
</dl>
<dl class="dlParallel dlCompact" id="section-9.5-7">
          <dt id="section-9.5-7.1">
              Client Metadata Name:</dt>
<dd id="section-9.5-7.2">
            <code>tls_client_auth_san_email</code><a href="#section-9.5-7.2" class="pilcrow">¶</a>
</dd>
<dt id="section-9.5-7.3">
              Client Metadata Description:</dt>
<dd id="section-9.5-7.4">String value specifying
              the expected rfc822Name SAN entry in the client certificate.<a href="#section-9.5-7.4" class="pilcrow">¶</a>
</dd>
<dt id="section-9.5-7.5">
              Change Controller:</dt>
<dd id="section-9.5-7.6">IESG<a href="#section-9.5-7.6" class="pilcrow">¶</a>
</dd>
<dt id="section-9.5-7.7">
              Specification Document(s):</dt>
<dd id="section-9.5-7.8">
            <a href="#client_metadata_pki" class="xref">Section 2.1.2</a> of RFC 8705<a href="#section-9.5-7.8" class="pilcrow">¶</a>
</dd>
</dl>
</section>
</section>
</div>
<section id="section-10">
      <h2 id="name-references">
<a href="#section-10" class="section-number selfRef">10. </a><a href="#name-references" class="section-name selfRef">References</a>
      </h2>
<section id="section-10.1">
        <h3 id="name-normative-references">
<a href="#section-10.1" class="section-number selfRef">10.1. </a><a href="#name-normative-references" class="section-name selfRef">Normative References</a>
        </h3>
<dl class="references">
<dt id="BCP195">[BCP195]</dt>
<dd>
<span class="refAuthor">Sheffer, Y.</span><span class="refAuthor">, Holz, R.</span><span class="refAuthor">, and P. Saint-Andre</span>, <span class="refTitle">"Recommendations for Secure Use of Transport Layer Security (TLS) and Datagram Transport Layer Security (DTLS)"</span>, <span class="seriesInfo">BCP 195</span>, <span class="seriesInfo">RFC 7525</span>, <time datetime="2015-05">May 2015</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/bcp195">https://www.rfc-editor.org/info/bcp195</a>&gt;</span>. </dd>
<dt id="RFC2119">[RFC2119]</dt>
<dd>
<span class="refAuthor">Bradner, S.</span>, <span class="refTitle">"Key words for use in RFCs to Indicate Requirement Levels"</span>, <span class="seriesInfo">BCP 14</span>, <span class="seriesInfo">RFC 2119</span>, <span class="seriesInfo">DOI 10.17487/RFC2119</span>, <time datetime="1997-03">March 1997</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc2119">https://www.rfc-editor.org/info/rfc2119</a>&gt;</span>. </dd>
<dt id="RFC4514">[RFC4514]</dt>
<dd>
<span class="refAuthor">Zeilenga, K., Ed.</span>, <span class="refTitle">"Lightweight Directory Access Protocol (LDAP): String Representation of Distinguished Names"</span>, <span class="seriesInfo">RFC 4514</span>, <span class="seriesInfo">DOI 10.17487/RFC4514</span>, <time datetime="2006-06">June 2006</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc4514">https://www.rfc-editor.org/info/rfc4514</a>&gt;</span>. </dd>
<dt id="RFC4648">[RFC4648]</dt>
<dd>
<span class="refAuthor">Josefsson, S.</span>, <span class="refTitle">"The Base16, Base32, and Base64 Data Encodings"</span>, <span class="seriesInfo">RFC 4648</span>, <span class="seriesInfo">DOI 10.17487/RFC4648</span>, <time datetime="2006-10">October 2006</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc4648">https://www.rfc-editor.org/info/rfc4648</a>&gt;</span>. </dd>
<dt id="RFC5246">[RFC5246]</dt>
<dd>
<span class="refAuthor">Dierks, T.</span><span class="refAuthor"> and E. Rescorla</span>, <span class="refTitle">"The Transport Layer Security (TLS) Protocol Version 1.2"</span>, <span class="seriesInfo">RFC 5246</span>, <span class="seriesInfo">DOI 10.17487/RFC5246</span>, <time datetime="2008-08">August 2008</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc5246">https://www.rfc-editor.org/info/rfc5246</a>&gt;</span>. </dd>
<dt id="RFC5280">[RFC5280]</dt>
<dd>
<span class="refAuthor">Cooper, D.</span><span class="refAuthor">, Santesson, S.</span><span class="refAuthor">, Farrell, S.</span><span class="refAuthor">, Boeyen, S.</span><span class="refAuthor">, Housley, R.</span><span class="refAuthor">, and W. Polk</span>, <span class="refTitle">"Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) Profile"</span>, <span class="seriesInfo">RFC 5280</span>, <span class="seriesInfo">DOI 10.17487/RFC5280</span>, <time datetime="2008-05">May 2008</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc5280">https://www.rfc-editor.org/info/rfc5280</a>&gt;</span>. </dd>
<dt id="RFC6749">[RFC6749]</dt>
<dd>
<span class="refAuthor">Hardt, D., Ed.</span>, <span class="refTitle">"The OAuth 2.0 Authorization Framework"</span>, <span class="seriesInfo">RFC 6749</span>, <span class="seriesInfo">DOI 10.17487/RFC6749</span>, <time datetime="2012-10">October 2012</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc6749">https://www.rfc-editor.org/info/rfc6749</a>&gt;</span>. </dd>
<dt id="RFC6750">[RFC6750]</dt>
<dd>
<span class="refAuthor">Jones, M.</span><span class="refAuthor"> and D. Hardt</span>, <span class="refTitle">"The OAuth 2.0 Authorization Framework: Bearer Token Usage"</span>, <span class="seriesInfo">RFC 6750</span>, <span class="seriesInfo">DOI 10.17487/RFC6750</span>, <time datetime="2012-10">October 2012</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc6750">https://www.rfc-editor.org/info/rfc6750</a>&gt;</span>. </dd>
<dt id="RFC7517">[RFC7517]</dt>
<dd>
<span class="refAuthor">Jones, M.</span>, <span class="refTitle">"JSON Web Key (JWK)"</span>, <span class="seriesInfo">RFC 7517</span>, <span class="seriesInfo">DOI 10.17487/RFC7517</span>, <time datetime="2015-05">May 2015</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc7517">https://www.rfc-editor.org/info/rfc7517</a>&gt;</span>. </dd>
<dt id="RFC7519">[RFC7519]</dt>
<dd>
<span class="refAuthor">Jones, M.</span><span class="refAuthor">, Bradley, J.</span><span class="refAuthor">, and N. Sakimura</span>, <span class="refTitle">"JSON Web Token (JWT)"</span>, <span class="seriesInfo">RFC 7519</span>, <span class="seriesInfo">DOI 10.17487/RFC7519</span>, <time datetime="2015-05">May 2015</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc7519">https://www.rfc-editor.org/info/rfc7519</a>&gt;</span>. </dd>
<dt id="RFC7591">[RFC7591]</dt>
<dd>
<span class="refAuthor">Richer, J., Ed.</span><span class="refAuthor">, Jones, M.</span><span class="refAuthor">, Bradley, J.</span><span class="refAuthor">, Machulak, M.</span><span class="refAuthor">, and P. Hunt</span>, <span class="refTitle">"OAuth 2.0 Dynamic Client Registration Protocol"</span>, <span class="seriesInfo">RFC 7591</span>, <span class="seriesInfo">DOI 10.17487/RFC7591</span>, <time datetime="2015-07">July 2015</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc7591">https://www.rfc-editor.org/info/rfc7591</a>&gt;</span>. </dd>
<dt id="RFC7662">[RFC7662]</dt>
<dd>
<span class="refAuthor">Richer, J., Ed.</span>, <span class="refTitle">"OAuth 2.0 Token Introspection"</span>, <span class="seriesInfo">RFC 7662</span>, <span class="seriesInfo">DOI 10.17487/RFC7662</span>, <time datetime="2015-10">October 2015</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc7662">https://www.rfc-editor.org/info/rfc7662</a>&gt;</span>. </dd>
<dt id="RFC7800">[RFC7800]</dt>
<dd>
<span class="refAuthor">Jones, M.</span><span class="refAuthor">, Bradley, J.</span><span class="refAuthor">, and H. Tschofenig</span>, <span class="refTitle">"Proof-of-Possession Key Semantics for JSON Web Tokens (JWTs)"</span>, <span class="seriesInfo">RFC 7800</span>, <span class="seriesInfo">DOI 10.17487/RFC7800</span>, <time datetime="2016-04">April 2016</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc7800">https://www.rfc-editor.org/info/rfc7800</a>&gt;</span>. </dd>
<dt id="RFC8174">[RFC8174]</dt>
<dd>
<span class="refAuthor">Leiba, B.</span>, <span class="refTitle">"Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words"</span>, <span class="seriesInfo">BCP 14</span>, <span class="seriesInfo">RFC 8174</span>, <span class="seriesInfo">DOI 10.17487/RFC8174</span>, <time datetime="2017-05">May 2017</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc8174">https://www.rfc-editor.org/info/rfc8174</a>&gt;</span>. </dd>
<dt id="RFC8414">[RFC8414]</dt>
<dd>
<span class="refAuthor">Jones, M.</span><span class="refAuthor">, Sakimura, N.</span><span class="refAuthor">, and J. Bradley</span>, <span class="refTitle">"OAuth 2.0 Authorization Server Metadata"</span>, <span class="seriesInfo">RFC 8414</span>, <span class="seriesInfo">DOI 10.17487/RFC8414</span>, <time datetime="2018-06">June 2018</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc8414">https://www.rfc-editor.org/info/rfc8414</a>&gt;</span>. </dd>
<dt id="RFC8446">[RFC8446]</dt>
<dd>
<span class="refAuthor">Rescorla, E.</span>, <span class="refTitle">"The Transport Layer Security (TLS) Protocol Version 1.3"</span>, <span class="seriesInfo">RFC 8446</span>, <span class="seriesInfo">DOI 10.17487/RFC8446</span>, <time datetime="2018-08">August 2018</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc8446">https://www.rfc-editor.org/info/rfc8446</a>&gt;</span>. </dd>
<dt id="SHS">[SHS]</dt>
<dd>
<span class="refAuthor">National Institute of Standards and Technology (NIST)</span>, <span class="refTitle">"Secure Hash Standard (SHS)"</span>, <span class="seriesInfo">FIPS PUB 180-4</span>, <span class="seriesInfo">DOI 10.6028/NIST.FIPS.180-4</span>, <time datetime="2015-08">August 2015</time>, <span>&lt;<a href="https://nvlpubs.nist.gov/nistpubs/FIPS/NIST.FIPS.180-4.pdf">https://nvlpubs.nist.gov/nistpubs/FIPS/NIST.FIPS.180-4.pdf</a>&gt;</span>. </dd>
<dt id="X690">[X690]</dt>
<dd>
<span class="refAuthor">ITU-T</span>, <span class="refTitle">"Information Technology - ASN.1 encoding rules: Specification of Basic Encoding Rules (BER), Canonical Encoding Rules (CER) and Distinguished Encoding Rules (DER)"</span>, <span class="seriesInfo">ITU-T Recommendation X.690</span>, <time datetime="2015-08">August 2015</time>. </dd>
</dl>
</section>
<section id="section-10.2">
        <h3 id="name-informative-references">
<a href="#section-10.2" class="section-number selfRef">10.2. </a><a href="#name-informative-references" class="section-name selfRef">Informative References</a>
        </h3>
<dl class="references">
<dt id="CX5P">[CX5P]</dt>
<dd>
<span class="refAuthor">Wong, D.</span>, <span class="refTitle">"Common x509 certificate validation/creation pitfalls"</span>, <time datetime="2016-09">September 2016</time>, <span>&lt;<a href="https://www.cryptologie.net/article/374/common-x509-certificate-validationcreation-pitfalls">https://www.cryptologie.net/article/374/common-x509-certificate-validationcreation-pitfalls</a>&gt;</span>. </dd>
<dt id="DCW">[DCW]</dt>
<dd>
<span class="refAuthor">Georgiev, M.</span><span class="refAuthor">, Iyengar, S.</span><span class="refAuthor">, Jana, S.</span><span class="refAuthor">, Anubhai, R.</span><span class="refAuthor">, Boneh, D.</span><span class="refAuthor">, and V. Shmatikov</span>, <span class="refTitle">"The Most Dangerous Code in the World: Validating SSL Certificates in Non-Browser Software"</span>, <span class="seriesInfo">DOI 10.1145/2382196.2382204</span>, <time datetime="2012-10">October 2012</time>, <span>&lt;<a href="http://www.cs.utexas.edu/~shmat/shmat_ccs12.pdf">http://www.cs.utexas.edu/~shmat/shmat_ccs12.pdf</a>&gt;</span>. </dd>
<dt id="IANA.JWT.Claims">[IANA.JWT.Claims]</dt>
<dd>
<span class="refAuthor">IANA</span>, <span class="refTitle">"JSON Web Token Claims"</span>, <span>&lt;<a href="https://www.iana.org/assignments/jwt">https://www.iana.org/assignments/jwt</a>&gt;</span>. </dd>
<dt id="IANA.OAuth.Parameters">[IANA.OAuth.Parameters]</dt>
<dd>
<span class="refAuthor">IANA</span>, <span class="refTitle">"OAuth Parameters"</span>, <span>&lt;<a href="https://www.iana.org/assignments/oauth-parameters">https://www.iana.org/assignments/oauth-parameters</a>&gt;</span>. </dd>
<dt id="OpenID.CIBA">[OpenID.CIBA]</dt>
<dd>
<span class="refAuthor">Fernandez, G.</span><span class="refAuthor">, Walter, F.</span><span class="refAuthor">, Nennker, A.</span><span class="refAuthor">, Tonge, D.</span><span class="refAuthor">, and B. Campbell</span>, <span class="refTitle">"OpenID Connect Client Initiated Backchannel Authentication Flow - Core 1.0"</span>, <time datetime="2019-01-16">16 January 2019</time>, <span>&lt;<a href="https://openid.net/specs/openid-client-initiated-backchannel-authentication-core-1_0.html">https://openid.net/specs/openid-client-initiated-backchannel-authentication-core-1_0.html</a>&gt;</span>. </dd>
<dt id="RFC4517">[RFC4517]</dt>
<dd>
<span class="refAuthor">Legg, S., Ed.</span>, <span class="refTitle">"Lightweight Directory Access Protocol (LDAP): Syntaxes and Matching Rules"</span>, <span class="seriesInfo">RFC 4517</span>, <span class="seriesInfo">DOI 10.17487/RFC4517</span>, <time datetime="2006-06">June 2006</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc4517">https://www.rfc-editor.org/info/rfc4517</a>&gt;</span>. </dd>
<dt id="RFC5952">[RFC5952]</dt>
<dd>
<span class="refAuthor">Kawamura, S.</span><span class="refAuthor"> and M. Kawashima</span>, <span class="refTitle">"A Recommendation for IPv6 Address Text Representation"</span>, <span class="seriesInfo">RFC 5952</span>, <span class="seriesInfo">DOI 10.17487/RFC5952</span>, <time datetime="2010-08">August 2010</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc5952">https://www.rfc-editor.org/info/rfc5952</a>&gt;</span>. </dd>
<dt id="RFC6066">[RFC6066]</dt>
<dd>
<span class="refAuthor">Eastlake 3rd, D.</span>, <span class="refTitle">"Transport Layer Security (TLS) Extensions: Extension Definitions"</span>, <span class="seriesInfo">RFC 6066</span>, <span class="seriesInfo">DOI 10.17487/RFC6066</span>, <time datetime="2011-01">January 2011</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc6066">https://www.rfc-editor.org/info/rfc6066</a>&gt;</span>. </dd>
<dt id="RFC7009">[RFC7009]</dt>
<dd>
<span class="refAuthor">Lodderstedt, T., Ed.</span><span class="refAuthor">, Dronia, S.</span><span class="refAuthor">, and M. Scurtescu</span>, <span class="refTitle">"OAuth 2.0 Token Revocation"</span>, <span class="seriesInfo">RFC 7009</span>, <span class="seriesInfo">DOI 10.17487/RFC7009</span>, <time datetime="2013-08">August 2013</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc7009">https://www.rfc-editor.org/info/rfc7009</a>&gt;</span>. </dd>
<dt id="RFC7518">[RFC7518]</dt>
<dd>
<span class="refAuthor">Jones, M.</span>, <span class="refTitle">"JSON Web Algorithms (JWA)"</span>, <span class="seriesInfo">RFC 7518</span>, <span class="seriesInfo">DOI 10.17487/RFC7518</span>, <time datetime="2015-05">May 2015</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc7518">https://www.rfc-editor.org/info/rfc7518</a>&gt;</span>. </dd>
<dt id="I-D.ietf-oauth-token-binding">[TOKEN]</dt>
<dd>
<span class="refAuthor">Jones, M.</span><span class="refAuthor">, Campbell, B.</span><span class="refAuthor">, Bradley, J.</span><span class="refAuthor">, and W. Denniss</span>, <span class="refTitle">"OAuth 2.0 Token Binding"</span>, <span class="refContent">Work in Progress</span>, <span class="seriesInfo">Internet-Draft, draft-ietf-oauth-token-binding-08</span>, <time datetime="2018-10-19">19 October 2018</time>, <span>&lt;<a href="https://tools.ietf.org/html/draft-ietf-oauth-token-binding-08">https://tools.ietf.org/html/draft-ietf-oauth-token-binding-08</a>&gt;</span>. </dd>
</dl>
</section>
</section>
<div id="example">
<section id="section-appendix.a">
      <h2 id="name-example-cnf-claim-certifica">
<a href="#section-appendix.a" class="section-number selfRef">Appendix A. </a><a href="#name-example-cnf-claim-certifica" class="section-name selfRef">Example "cnf" Claim, Certificate, and JWK</a>
      </h2>
<p id="section-appendix.a-1">
        For reference, an <code>x5t#S256</code> value and the X.509 certificate
        from which it was calculated are provided in the following examples,
        Figures <a href="#cnf" class="xref">5</a> and <a href="#pem" class="xref">6</a>, respectively. A JWK representation of the
        certificate's public key along with the <code>x5c</code> member is also
        provided in <a href="#jwk" class="xref">Figure 7</a>.<a href="#section-appendix.a-1" class="pilcrow">¶</a></p>
<span id="name-x5ts256-confirmation-claim"></span><div id="cnf">
<figure id="figure-5">
        <div id="section-appendix.a-2.1">
<pre class="sourcecode lang-json">
"cnf":{"x5t#S256":"A4DtL2JmUMhAsvJj5tKyn64SqzmuXbMrJa0n761y5v0"}
</pre>
</div>
<figcaption><a href="#figure-5" class="selfRef">Figure 5</a>:
<a href="#name-x5ts256-confirmation-claim" class="selfRef">x5t#S256 Confirmation Claim</a>
        </figcaption></figure>
</div>
<span id="name-pem-encoded-self-signed-cer"></span><div id="pem">
<figure id="figure-6">
        <div class="artwork art-text alignLeft" id="section-appendix.a-3.1">
<pre>
-----BEGIN CERTIFICATE-----
MIIBBjCBrAIBAjAKBggqhkjOPQQDAjAPMQ0wCwYDVQQDDARtdGxzMB4XDTE4MTAx
ODEyMzcwOVoXDTIyMDUwMjEyMzcwOVowDzENMAsGA1UEAwwEbXRsczBZMBMGByqG
SM49AgEGCCqGSM49AwEHA0IABNcnyxwqV6hY8QnhxxzFQ03C7HKW9OylMbnQZjjJ
/Au08/coZwxS7LfA4vOLS9WuneIXhbGGWvsDSb0tH6IxLm8wCgYIKoZIzj0EAwID
SQAwRgIhAP0RC1E+vwJD/D1AGHGzuri+hlV/PpQEKTWUVeORWz83AiEA5x2eXZOV
bUlJSGQgjwD5vaUaKlLR50Q2DmFfQj1L+SY=
-----END CERTIFICATE-----</pre>
</div>
<figcaption><a href="#figure-6" class="selfRef">Figure 6</a>:
<a href="#name-pem-encoded-self-signed-cer" class="selfRef">PEM Encoded Self-Signed Certificate</a>
        </figcaption></figure>
</div>
<span id="name-json-web-key"></span><div id="jwk">
<figure id="figure-7">
        <div id="section-appendix.a-4.1">
<pre class="sourcecode lang-json">
{
 "kty":"EC",
 "x":"1yfLHCpXqFjxCeHHHMVDTcLscpb07KUxudBmOMn8C7Q",
 "y":"8_coZwxS7LfA4vOLS9WuneIXhbGGWvsDSb0tH6IxLm8",
 "crv":"P-256",
 "x5c":[
  "MIIBBjCBrAIBAjAKBggqhkjOPQQDAjAPMQ0wCwYDVQQDDARtdGxzMB4XDTE4MTA
   xODEyMzcwOVoXDTIyMDUwMjEyMzcwOVowDzENMAsGA1UEAwwEbXRsczBZMBMGBy
   qGSM49AgEGCCqGSM49AwEHA0IABNcnyxwqV6hY8QnhxxzFQ03C7HKW9OylMbnQZ
   jjJ/Au08/coZwxS7LfA4vOLS9WuneIXhbGGWvsDSb0tH6IxLm8wCgYIKoZIzj0E
   AwIDSQAwRgIhAP0RC1E+vwJD/D1AGHGzuri+hlV/PpQEKTWUVeORWz83AiEA5x2
   eXZOVbUlJSGQgjwD5vaUaKlLR50Q2DmFfQj1L+SY="
   ]
 }</pre>
</div>
<figcaption><a href="#figure-7" class="selfRef">Figure 7</a>:
<a href="#name-json-web-key" class="selfRef">JSON Web Key</a>
        </figcaption></figure>
</div>
</section>
</div>
<div id="relation">
<section id="section-appendix.b">
      <h2 id="name-relationship-to-token-bindi">
<a href="#section-appendix.b" class="section-number selfRef">Appendix B. </a><a href="#name-relationship-to-token-bindi" class="section-name selfRef">Relationship to Token Binding</a>
      </h2>
<p id="section-appendix.b-1">
        OAuth 2.0 Token Binding <span>[<a href="#I-D.ietf-oauth-token-binding" class="xref">TOKEN</a>]</span>
        enables the application of Token Binding to the various artifacts and tokens employed throughout OAuth.
        That includes binding of an access token to a Token Binding key, which bears some similarities in motivation
        and design to the mutual-TLS client certificate-bound access tokens defined in this document.
        Both documents define what is often called a proof-of-possession security mechanism
        for access tokens, whereby a client must demonstrate possession of cryptographic keying
        material when accessing a protected resource. The details differ somewhat between the two documents but both
        have the authorization server bind the access token that it issues to an asymmetric key pair
        held by the client. The client then proves possession of the private key from that pair
        with respect to the TLS connection over which the protected resource is accessed.<a href="#section-appendix.b-1" class="pilcrow">¶</a></p>
<p id="section-appendix.b-2">
        Token Binding uses bare keys that are generated on the client,
        which avoids many of the difficulties of creating, distributing, and managing certificates
        used in this specification. However, at the time of
        writing, Token Binding is fairly new, and there is relatively little support for it in available
        application development platforms and tooling. Until better support for the underlying
        core Token Binding specifications exists, practical implementations of OAuth 2.0 Token Binding
        are infeasible. 
        Mutual TLS, on the other hand, has been around for some time and enjoys
        widespread support in web servers and development platforms. As a consequence, OAuth 2.0 Mutual-TLS
        Client Authentication and Certificate-Bound Access Tokens can be
        built and deployed now using existing platforms and tools.
        In the future, the two specifications are likely to be
        deployed in parallel for solving similar problems in different environments.
        Authorization servers may even support both specifications simultaneously using different
        proof-of-possession mechanisms for tokens issued to different clients.<a href="#section-appendix.b-2" class="pilcrow">¶</a></p>
</section>
</div>
<div id="Acknowledgements">
<section id="section-appendix.c">
      <h2 id="name-acknowledgements">
<a href="#name-acknowledgements" class="section-name selfRef">Acknowledgements</a>
      </h2>
<p id="section-appendix.c-1">
        Scott "not Tomlinson" Tomilson and <span class="contact-name">Matt Peterson</span> were involved in
        design and development work on a mutual-TLS OAuth client authentication
        implementation that predates this document. Experience and learning from that work
        informed some of the content of this document.<a href="#section-appendix.c-1" class="pilcrow">¶</a></p>
<p id="section-appendix.c-2">
        This specification was developed within the OAuth Working Group
        under the chairmanship of <span class="contact-name">Hannes Tschofenig</span>
        and <span class="contact-name">Rifaat Shekh-Yusef</span> with <span class="contact-name">Eric Rescorla</span>,
 <span class="contact-name">Benjamin Kaduk</span>, and
 <span class="contact-name">Roman Danyliw</span>
        serving as Security Area Directors. Additionally, the following
        individuals contributed ideas, feedback, and wording
        that helped shape this specification:

 <span class="contact-name">Vittorio Bertocci</span>,
        <span class="contact-name">Sergey Beryozkin</span>,
        <span class="contact-name">Ralph Bragg</span>,
        <span class="contact-name">Sophie Bremer</span>,
        <span class="contact-name">Roman Danyliw</span>,
        <span class="contact-name">Vladimir Dzhuvinov</span>,
        <span class="contact-name">Samuel Erdtman</span>,
        <span class="contact-name">Evan Gilman</span>,
        <span class="contact-name">Leif Johansson</span>,
        <span class="contact-name">Michael Jones</span>,
        <span class="contact-name">Phil Hunt</span>,
        <span class="contact-name">Benjamin Kaduk</span>,
        <span class="contact-name">Takahiko Kawasaki</span>,
        <span class="contact-name">Sean Leonard</span>,
        <span class="contact-name">Kepeng Li</span>,
        <span class="contact-name">Neil Madden</span>,
        <span class="contact-name">James Manger</span>,
        <span class="contact-name">Jim Manico</span>,
        <span class="contact-name">Nov Matake</span>,
        <span class="contact-name">Sascha Preibisch</span>,
        <span class="contact-name">Eric Rescorla</span>,
        <span class="contact-name">Justin Richer</span>,
        <span class="contact-name">Vincent Roca</span>,
        <span class="contact-name">Filip Skokan</span>,
        <span class="contact-name">Dave Tonge</span>,
        and
        <span class="contact-name">Hannes Tschofenig</span>.<a href="#section-appendix.c-2" class="pilcrow">¶</a></p>
</section>
</div>
<div id="authors-addresses">
<section id="section-appendix.d">
      <h2 id="name-authors-addresses">
<a href="#name-authors-addresses" class="section-name selfRef">Authors' Addresses</a>
      </h2>
<address class="vcard">
        <div dir="auto" class="left"><span class="fn nameRole">Brian Campbell</span></div>
<div dir="auto" class="left"><span class="org">Ping Identity</span></div>
<div class="email">
<span>Email:</span>
<a href="mailto:brian.d.campbell@gmail.com" class="email">brian.d.campbell@gmail.com</a>
</div>
</address>
<address class="vcard">
        <div dir="auto" class="left"><span class="fn nameRole">John Bradley</span></div>
<div dir="auto" class="left"><span class="org">Yubico</span></div>
<div class="email">
<span>Email:</span>
<a href="mailto:ve7jtb@ve7jtb.com" class="email">ve7jtb@ve7jtb.com</a>
</div>
<div class="url">
<span>URI:</span>
<a href="http://www.thread-safe.com/" class="url">http://www.thread-safe.com/</a>
</div>
</address>
<address class="vcard">
        <div dir="auto" class="left"><span class="fn nameRole">Nat Sakimura</span></div>
<div dir="auto" class="left"><span class="org">Nomura Research Institute</span></div>
<div class="email">
<span>Email:</span>
<a href="mailto:n-sakimura@nri.co.jp" class="email">n-sakimura@nri.co.jp</a>
</div>
<div class="url">
<span>URI:</span>
<a href="https://nat.sakimura.org/" class="url">https://nat.sakimura.org/</a>
</div>
</address>
<address class="vcard">
        <div dir="auto" class="left"><span class="fn nameRole">Torsten Lodderstedt</span></div>
<div dir="auto" class="left"><span class="org">YES.com AG</span></div>
<div class="email">
<span>Email:</span>
<a href="mailto:torsten@lodderstedt.net" class="email">torsten@lodderstedt.net</a>
</div>
</address>
</section>
</div>
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