<pre>Internet Engineering Task Force (IETF)                  R. Fielding, Ed.
Request for Comments: 7235                                         Adobe
Obsoletes: <a href="./rfc2616">2616</a>                                          J. Reschke, Ed.
Updates: <a href="./rfc2617">2617</a>                                                 greenbytes
Category: Standards Track                                      June 2014
ISSN: 2070-1721


         <span class="h1">Hypertext Transfer Protocol (HTTP/1.1): Authentication</span>

Abstract

   The Hypertext Transfer Protocol (HTTP) is a stateless application-
   level protocol for distributed, collaborative, hypermedia information
   systems.  This document defines the HTTP Authentication framework.

Status of This Memo

   This is an Internet Standards Track document.

   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 <a href="./rfc5741#section-2">Section&nbsp;2 of RFC 5741</a>.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   <a href="http://www.rfc-editor.org/info/rfc7235">http://www.rfc-editor.org/info/rfc7235</a>.

Copyright Notice

   Copyright (c) 2014 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to <a href="https://www.rfc-editor.org/bcp/bcp78">BCP 78</a> and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (<a href="http://trustee.ietf.org/license-info">http://trustee.ietf.org/license-info</a>) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

   This document may contain material from IETF Documents or IETF
   Contributions published or made publicly available before November
   10, 2008.  The person(s) controlling the copyright in some of this



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   material may not have granted the IETF Trust the right to allow
   modifications of such material outside the IETF Standards Process.
   Without obtaining an adequate license from the person(s) controlling
   the copyright in such materials, this document may not be modified
   outside the IETF Standards Process, and derivative works of it may
   not be created outside the IETF Standards Process, except to format
   it for publication as an RFC or to translate it into languages other
   than English.

Table of Contents

   <a href="#section-1">1</a>. Introduction ....................................................<a href="#page-3">3</a>
      <a href="#section-1.1">1.1</a>. Conformance and Error Handling .............................<a href="#page-3">3</a>
      <a href="#section-1.2">1.2</a>. Syntax Notation ............................................<a href="#page-3">3</a>
   <a href="#section-2">2</a>. Access Authentication Framework .................................<a href="#page-3">3</a>
      <a href="#section-2.1">2.1</a>. Challenge and Response .....................................<a href="#page-3">3</a>
      <a href="#section-2.2">2.2</a>. Protection Space (Realm) ...................................<a href="#page-5">5</a>
   <a href="#section-3">3</a>. Status Code Definitions .........................................<a href="#page-6">6</a>
      <a href="#section-3.1">3.1</a>. 401 Unauthorized ...........................................<a href="#page-6">6</a>
      <a href="#section-3.2">3.2</a>. 407 Proxy Authentication Required ..........................<a href="#page-6">6</a>
   <a href="#section-4">4</a>. Header Field Definitions ........................................<a href="#page-7">7</a>
      <a href="#section-4.1">4.1</a>. WWW-Authenticate ...........................................<a href="#page-7">7</a>
      <a href="#section-4.2">4.2</a>. Authorization ..............................................<a href="#page-8">8</a>
      <a href="#section-4.3">4.3</a>. Proxy-Authenticate .........................................<a href="#page-8">8</a>
      <a href="#section-4.4">4.4</a>. Proxy-Authorization ........................................<a href="#page-9">9</a>
   <a href="#section-5">5</a>. IANA Considerations .............................................<a href="#page-9">9</a>
      <a href="#section-5.1">5.1</a>. Authentication Scheme Registry .............................<a href="#page-9">9</a>
           <a href="#section-5.1.1">5.1.1</a>. Procedure ...........................................<a href="#page-9">9</a>
           <a href="#section-5.1.2">5.1.2</a>. Considerations for New Authentication Schemes ......<a href="#page-10">10</a>
      <a href="#section-5.2">5.2</a>. Status Code Registration ..................................<a href="#page-11">11</a>
      <a href="#section-5.3">5.3</a>. Header Field Registration .................................<a href="#page-11">11</a>
   <a href="#section-6">6</a>. Security Considerations ........................................<a href="#page-12">12</a>
      <a href="#section-6.1">6.1</a>. Confidentiality of Credentials ............................<a href="#page-12">12</a>
      <a href="#section-6.2">6.2</a>. Authentication Credentials and Idle Clients ...............<a href="#page-12">12</a>
      <a href="#section-6.3">6.3</a>. Protection Spaces .........................................<a href="#page-13">13</a>
   <a href="#section-7">7</a>. Acknowledgments ................................................<a href="#page-14">14</a>
   <a href="#section-8">8</a>. References .....................................................<a href="#page-14">14</a>
      <a href="#section-8.1">8.1</a>. Normative References ......................................<a href="#page-14">14</a>
      <a href="#section-8.2">8.2</a>. Informative References ....................................<a href="#page-14">14</a>
   <a href="#appendix-A">Appendix A</a>. Changes from RFCs 2616 and 2617 .......................<a href="#page-16">16</a>
   <a href="#appendix-B">Appendix B</a>. Imported ABNF .........................................<a href="#page-16">16</a>
   <a href="#appendix-C">Appendix C</a>. Collected ABNF ........................................<a href="#page-17">17</a>
   Index .............................................................<a href="#page-18">18</a>








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<span class="h2"><a class="selflink" id="section-1" href="#section-1">1</a>.  Introduction</span>

   HTTP provides a general framework for access control and
   authentication, via an extensible set of challenge-response
   authentication schemes, which can be used by a server to challenge a
   client request and by a client to provide authentication information.
   This document defines HTTP/1.1 authentication in terms of the
   architecture defined in "Hypertext Transfer Protocol (HTTP/1.1):
   Message Syntax and Routing" [<a href="./rfc7230" title="&quot;Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing&quot;">RFC7230</a>], including the general
   framework previously described in "HTTP Authentication: Basic and
   Digest Access Authentication" [<a href="./rfc2617" title="&quot;HTTP Authentication: Basic and Digest Access Authentication&quot;">RFC2617</a>] and the related fields and
   status codes previously defined in "Hypertext Transfer Protocol --
   HTTP/1.1" [<a href="./rfc2616" title="&quot;Hypertext Transfer Protocol -- HTTP/1.1&quot;">RFC2616</a>].

   The IANA Authentication Scheme Registry (<a href="#section-5.1">Section 5.1</a>) lists
   registered authentication schemes and their corresponding
   specifications, including the "basic" and "digest" authentication
   schemes previously defined by <a href="./rfc2617">RFC 2617</a>.

<span class="h3"><a class="selflink" id="section-1.1" href="#section-1.1">1.1</a>.  Conformance and Error Handling</span>

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [<a href="./rfc2119" title="&quot;Key words for use in RFCs to Indicate Requirement Levels&quot;">RFC2119</a>].

   Conformance criteria and considerations regarding error handling are
   defined in <a href="./rfc7230#section-2.5">Section&nbsp;2.5 of [RFC7230]</a>.

<span class="h3"><a class="selflink" id="section-1.2" href="#section-1.2">1.2</a>.  Syntax Notation</span>

   This specification uses the Augmented Backus-Naur Form (ABNF)
   notation of [<a href="./rfc5234" title="&quot;Augmented BNF for Syntax Specifications: ABNF&quot;">RFC5234</a>] with a list extension, defined in <a href="./rfc7230#section-7">Section&nbsp;7 of
   [RFC7230]</a>, that allows for compact definition of comma-separated
   lists using a '#' operator (similar to how the '*' operator indicates
   repetition).  <a href="#appendix-B">Appendix B</a> describes rules imported from other
   documents.  <a href="#appendix-C">Appendix C</a> shows the collected grammar with all list
   operators expanded to standard ABNF notation.

<span class="h2"><a class="selflink" id="section-2" href="#section-2">2</a>.  Access Authentication Framework</span>

<span class="h3"><a class="selflink" id="section-2.1" href="#section-2.1">2.1</a>.  Challenge and Response</span>

   HTTP provides a simple challenge-response authentication framework
   that can be used by a server to challenge a client request and by a
   client to provide authentication information.  It uses a case-
   insensitive token as a means to identify the authentication scheme,
   followed by additional information necessary for achieving




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   authentication via that scheme.  The latter can be either a comma-
   separated list of parameters or a single sequence of characters
   capable of holding base64-encoded information.

   Authentication parameters are name=value pairs, where the name token
   is matched case-insensitively, and each parameter name MUST only
   occur once per challenge.

     auth-scheme    = token

     auth-param     = token BWS "=" BWS ( token / quoted-string )

     token68        = 1*( ALPHA / DIGIT /
                          "-" / "." / "_" / "~" / "+" / "/" ) *"="

   The token68 syntax allows the 66 unreserved URI characters
   ([<a href="./rfc3986" title="&quot;Uniform Resource Identifier (URI): Generic Syntax&quot;">RFC3986</a>]), plus a few others, so that it can hold a base64,
   base64url (URL and filename safe alphabet), base32, or base16 (hex)
   encoding, with or without padding, but excluding whitespace
   ([<a href="./rfc4648" title="&quot;The Base16, Base32, and Base64 Data Encodings&quot;">RFC4648</a>]).

   A 401 (Unauthorized) response message is used by an origin server to
   challenge the authorization of a user agent, including a
   WWW-Authenticate header field containing at least one challenge
   applicable to the requested resource.

   A 407 (Proxy Authentication Required) response message is used by a
   proxy to challenge the authorization of a client, including a
   Proxy-Authenticate header field containing at least one challenge
   applicable to the proxy for the requested resource.

     challenge   = auth-scheme [ 1*SP ( token68 / #auth-param ) ]

      Note: Many clients fail to parse a challenge that contains an
      unknown scheme.  A workaround for this problem is to list well-
      supported schemes (such as "basic") first.

   A user agent that wishes to authenticate itself with an origin server
   -- usually, but not necessarily, after receiving a 401 (Unauthorized)
   -- can do so by including an Authorization header field with the
   request.

   A client that wishes to authenticate itself with a proxy -- usually,
   but not necessarily, after receiving a 407 (Proxy Authentication
   Required) -- can do so by including a Proxy-Authorization header
   field with the request.





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   Both the Authorization field value and the Proxy-Authorization field
   value contain the client's credentials for the realm of the resource
   being requested, based upon a challenge received in a response
   (possibly at some point in the past).  When creating their values,
   the user agent ought to do so by selecting the challenge with what it
   considers to be the most secure auth-scheme that it understands,
   obtaining credentials from the user as appropriate.  Transmission of
   credentials within header field values implies significant security
   considerations regarding the confidentiality of the underlying
   connection, as described in <a href="#section-6.1">Section 6.1</a>.

     credentials = auth-scheme [ 1*SP ( token68 / #auth-param ) ]

   Upon receipt of a request for a protected resource that omits
   credentials, contains invalid credentials (e.g., a bad password) or
   partial credentials (e.g., when the authentication scheme requires
   more than one round trip), an origin server SHOULD send a 401
   (Unauthorized) response that contains a WWW-Authenticate header field
   with at least one (possibly new) challenge applicable to the
   requested resource.

   Likewise, upon receipt of a request that omits proxy credentials or
   contains invalid or partial proxy credentials, a proxy that requires
   authentication SHOULD generate a 407 (Proxy Authentication Required)
   response that contains a Proxy-Authenticate header field with at
   least one (possibly new) challenge applicable to the proxy.

   A server that receives valid credentials that are not adequate to
   gain access ought to respond with the 403 (Forbidden) status code
   (<a href="./rfc7231#section-6.5.3">Section&nbsp;6.5.3 of [RFC7231]</a>).

   HTTP does not restrict applications to this simple challenge-response
   framework for access authentication.  Additional mechanisms can be
   used, such as authentication at the transport level or via message
   encapsulation, and with additional header fields specifying
   authentication information.  However, such additional mechanisms are
   not defined by this specification.

<span class="h3"><a class="selflink" id="section-2.2" href="#section-2.2">2.2</a>.  Protection Space (Realm)</span>

   The "realm" authentication parameter is reserved for use by
   authentication schemes that wish to indicate a scope of protection.

   A protection space is defined by the canonical root URI (the scheme
   and authority components of the effective request URI; see <a href="./rfc7230#section-5.5">Section</a>
   <a href="./rfc7230#section-5.5">5.5 of [RFC7230]</a>) of the server being accessed, in combination with
   the realm value if present.  These realms allow the protected
   resources on a server to be partitioned into a set of protection



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   spaces, each with its own authentication scheme and/or authorization
   database.  The realm value is a string, generally assigned by the
   origin server, that can have additional semantics specific to the
   authentication scheme.  Note that a response can have multiple
   challenges with the same auth-scheme but with different realms.

   The protection space determines the domain over which credentials can
   be automatically applied.  If a prior request has been authorized,
   the user agent MAY reuse the same credentials for all other requests
   within that protection space for a period of time determined by the
   authentication scheme, parameters, and/or user preferences (such as a
   configurable inactivity timeout).  Unless specifically allowed by the
   authentication scheme, a single protection space cannot extend
   outside the scope of its server.

   For historical reasons, a sender MUST only generate the quoted-string
   syntax.  Recipients might have to support both token and
   quoted-string syntax for maximum interoperability with existing
   clients that have been accepting both notations for a long time.

<span class="h2"><a class="selflink" id="section-3" href="#section-3">3</a>.  Status Code Definitions</span>

<span class="h3"><a class="selflink" id="section-3.1" href="#section-3.1">3.1</a>.  401 Unauthorized</span>

   The 401 (Unauthorized) status code indicates that the request has not
   been applied because it lacks valid authentication credentials for
   the target resource.  The server generating a 401 response MUST send
   a WWW-Authenticate header field (<a href="#section-4.1">Section 4.1</a>) containing at least one
   challenge applicable to the target resource.

   If the request included authentication credentials, then the 401
   response indicates that authorization has been refused for those
   credentials.  The user agent MAY repeat the request with a new or
   replaced Authorization header field (<a href="#section-4.2">Section 4.2</a>).  If the 401
   response contains the same challenge as the prior response, and the
   user agent has already attempted authentication at least once, then
   the user agent SHOULD present the enclosed representation to the
   user, since it usually contains relevant diagnostic information.

<span class="h3"><a class="selflink" id="section-3.2" href="#section-3.2">3.2</a>.  407 Proxy Authentication Required</span>

   The 407 (Proxy Authentication Required) status code is similar to 401
   (Unauthorized), but it indicates that the client needs to
   authenticate itself in order to use a proxy.  The proxy MUST send a
   Proxy-Authenticate header field (<a href="#section-4.3">Section 4.3</a>) containing a challenge
   applicable to that proxy for the target resource.  The client MAY
   repeat the request with a new or replaced Proxy-Authorization header
   field (<a href="#section-4.4">Section 4.4</a>).



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<span class="h2"><a class="selflink" id="section-4" href="#section-4">4</a>.  Header Field Definitions</span>

   This section defines the syntax and semantics of header fields
   related to the HTTP authentication framework.

<span class="h3"><a class="selflink" id="section-4.1" href="#section-4.1">4.1</a>.  WWW-Authenticate</span>

   The "WWW-Authenticate" header field indicates the authentication
   scheme(s) and parameters applicable to the target resource.

     WWW-Authenticate = 1#challenge

   A server generating a 401 (Unauthorized) response MUST send a
   WWW-Authenticate header field containing at least one challenge.  A
   server MAY generate a WWW-Authenticate header field in other response
   messages to indicate that supplying credentials (or different
   credentials) might affect the response.

   A proxy forwarding a response MUST NOT modify any WWW-Authenticate
   fields in that response.

   User agents are advised to take special care in parsing the field
   value, as it might contain more than one challenge, and each
   challenge can contain a comma-separated list of authentication
   parameters.  Furthermore, the header field itself can occur multiple
   times.

   For instance:

     WWW-Authenticate: Newauth realm="apps", type=1,
                       title="Login to \"apps\"", Basic realm="simple"

   This header field contains two challenges; one for the "Newauth"
   scheme with a realm value of "apps", and two additional parameters
   "type" and "title", and another one for the "Basic" scheme with a
   realm value of "simple".

      Note: The challenge grammar production uses the list syntax as
      well.  Therefore, a sequence of comma, whitespace, and comma can
      be considered either as applying to the preceding challenge, or to
      be an empty entry in the list of challenges.  In practice, this
      ambiguity does not affect the semantics of the header field value
      and thus is harmless.








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<span class="h3"><a class="selflink" id="section-4.2" href="#section-4.2">4.2</a>.  Authorization</span>

   The "Authorization" header field allows a user agent to authenticate
   itself with an origin server -- usually, but not necessarily, after
   receiving a 401 (Unauthorized) response.  Its value consists of
   credentials containing the authentication information of the user
   agent for the realm of the resource being requested.

     Authorization = credentials

   If a request is authenticated and a realm specified, the same
   credentials are presumed to be valid for all other requests within
   this realm (assuming that the authentication scheme itself does not
   require otherwise, such as credentials that vary according to a
   challenge value or using synchronized clocks).

   A proxy forwarding a request MUST NOT modify any Authorization fields
   in that request.  See <a href="./rfc7234#section-3.2">Section&nbsp;3.2 of [RFC7234]</a> for details of and
   requirements pertaining to handling of the Authorization field by
   HTTP caches.

<span class="h3"><a class="selflink" id="section-4.3" href="#section-4.3">4.3</a>.  Proxy-Authenticate</span>

   The "Proxy-Authenticate" header field consists of at least one
   challenge that indicates the authentication scheme(s) and parameters
   applicable to the proxy for this effective request URI (<a href="./rfc7230#section-5.5">Section&nbsp;5.5
   of [RFC7230]</a>).  A proxy MUST send at least one Proxy-Authenticate
   header field in each 407 (Proxy Authentication Required) response
   that it generates.

     Proxy-Authenticate = 1#challenge

   Unlike WWW-Authenticate, the Proxy-Authenticate header field applies
   only to the next outbound client on the response chain.  This is
   because only the client that chose a given proxy is likely to have
   the credentials necessary for authentication.  However, when multiple
   proxies are used within the same administrative domain, such as
   office and regional caching proxies within a large corporate network,
   it is common for credentials to be generated by the user agent and
   passed through the hierarchy until consumed.  Hence, in such a
   configuration, it will appear as if Proxy-Authenticate is being
   forwarded because each proxy will send the same challenge set.

   Note that the parsing considerations for WWW-Authenticate apply to
   this header field as well; see <a href="#section-4.1">Section 4.1</a> for details.






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<span class="h3"><a class="selflink" id="section-4.4" href="#section-4.4">4.4</a>.  Proxy-Authorization</span>

   The "Proxy-Authorization" header field allows the client to identify
   itself (or its user) to a proxy that requires authentication.  Its
   value consists of credentials containing the authentication
   information of the client for the proxy and/or realm of the resource
   being requested.

     Proxy-Authorization = credentials

   Unlike Authorization, the Proxy-Authorization header field applies
   only to the next inbound proxy that demanded authentication using the
   Proxy-Authenticate field.  When multiple proxies are used in a chain,
   the Proxy-Authorization header field is consumed by the first inbound
   proxy that was expecting to receive credentials.  A proxy MAY relay
   the credentials from the client request to the next proxy if that is
   the mechanism by which the proxies cooperatively authenticate a given
   request.

<span class="h2"><a class="selflink" id="section-5" href="#section-5">5</a>.  IANA Considerations</span>

<span class="h3"><a class="selflink" id="section-5.1" href="#section-5.1">5.1</a>.  Authentication Scheme Registry</span>

   The "Hypertext Transfer Protocol (HTTP) Authentication Scheme
   Registry" defines the namespace for the authentication schemes in
   challenges and credentials.  It has been created and is now
   maintained at &lt;<a href="http://www.iana.org/assignments/http-authschemes">http://www.iana.org/assignments/http-authschemes</a>&gt;.

<span class="h4"><a class="selflink" id="section-5.1.1" href="#section-5.1.1">5.1.1</a>.  Procedure</span>

   Registrations MUST include the following fields:

   o  Authentication Scheme Name

   o  Pointer to specification text

   o  Notes (optional)

   Values to be added to this namespace require IETF Review (see
   <a href="./rfc5226#section-4.1">[RFC5226], Section&nbsp;4.1</a>).











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<span class="h4"><a class="selflink" id="section-5.1.2" href="#section-5.1.2">5.1.2</a>.  Considerations for New Authentication Schemes</span>

   There are certain aspects of the HTTP Authentication Framework that
   put constraints on how new authentication schemes can work:

   o  HTTP authentication is presumed to be stateless: all of the
      information necessary to authenticate a request MUST be provided
      in the request, rather than be dependent on the server remembering
      prior requests.  Authentication based on, or bound to, the
      underlying connection is outside the scope of this specification
      and inherently flawed unless steps are taken to ensure that the
      connection cannot be used by any party other than the
      authenticated user (see <a href="./rfc7230#section-2.3">Section&nbsp;2.3 of [RFC7230]</a>).

   o  The authentication parameter "realm" is reserved for defining
      protection spaces as described in <a href="#section-2.2">Section 2.2</a>.  New schemes MUST
      NOT use it in a way incompatible with that definition.

   o  The "token68" notation was introduced for compatibility with
      existing authentication schemes and can only be used once per
      challenge or credential.  Thus, new schemes ought to use the
      auth-param syntax instead, because otherwise future extensions
      will be impossible.

   o  The parsing of challenges and credentials is defined by this
      specification and cannot be modified by new authentication
      schemes.  When the auth-param syntax is used, all parameters ought
      to support both token and quoted-string syntax, and syntactical
      constraints ought to be defined on the field value after parsing
      (i.e., quoted-string processing).  This is necessary so that
      recipients can use a generic parser that applies to all
      authentication schemes.

      Note: The fact that the value syntax for the "realm" parameter is
      restricted to quoted-string was a bad design choice not to be
      repeated for new parameters.

   o  Definitions of new schemes ought to define the treatment of
      unknown extension parameters.  In general, a "must-ignore" rule is
      preferable to a "must-understand" rule, because otherwise it will
      be hard to introduce new parameters in the presence of legacy
      recipients.  Furthermore, it's good to describe the policy for
      defining new parameters (such as "update the specification" or
      "use this registry").

   o  Authentication schemes need to document whether they are usable in
      origin-server authentication (i.e., using WWW-Authenticate),
      and/or proxy authentication (i.e., using Proxy-Authenticate).



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   o  The credentials carried in an Authorization header field are
      specific to the user agent and, therefore, have the same effect on
      HTTP caches as the "private" Cache-Control response directive
      (<a href="./rfc7234#section-5.2.2.6">Section&nbsp;5.2.2.6 of [RFC7234]</a>), within the scope of the request in
      which they appear.

      Therefore, new authentication schemes that choose not to carry
      credentials in the Authorization header field (e.g., using a newly
      defined header field) will need to explicitly disallow caching, by
      mandating the use of either Cache-Control request directives
      (e.g., "no-store", <a href="./rfc7234#section-5.2.1.5">Section&nbsp;5.2.1.5 of [RFC7234]</a>) or response
      directives (e.g., "private").

<span class="h3"><a class="selflink" id="section-5.2" href="#section-5.2">5.2</a>.  Status Code Registration</span>

   The "Hypertext Transfer Protocol (HTTP) Status Code Registry" located
   at &lt;<a href="http://www.iana.org/assignments/http-status-codes">http://www.iana.org/assignments/http-status-codes</a>&gt; has been
   updated with the registrations below:

   +-------+-------------------------------+-------------+
   | Value | Description                   | Reference   |
   +-------+-------------------------------+-------------+
   | 401   | Unauthorized                  | <a href="#section-3.1">Section 3.1</a> |
   | 407   | Proxy Authentication Required | <a href="#section-3.2">Section 3.2</a> |
   +-------+-------------------------------+-------------+

<span class="h3"><a class="selflink" id="section-5.3" href="#section-5.3">5.3</a>.  Header Field Registration</span>

   HTTP header fields are registered within the "Message Headers"
   registry maintained at
   &lt;<a href="http://www.iana.org/assignments/message-headers/">http://www.iana.org/assignments/message-headers/</a>&gt;.

   This document defines the following HTTP header fields, so the
   "Permanent Message Header Field Names" registry has been updated
   accordingly (see [<a href="#ref-BCP90" title="&quot;Registration Procedures for Message Header Fields&quot;">BCP90</a>]).

   +---------------------+----------+----------+-------------+
   | Header Field Name   | Protocol | Status   | Reference   |
   +---------------------+----------+----------+-------------+
   | Authorization       | http     | standard | <a href="#section-4.2">Section 4.2</a> |
   | Proxy-Authenticate  | http     | standard | <a href="#section-4.3">Section 4.3</a> |
   | Proxy-Authorization | http     | standard | <a href="#section-4.4">Section 4.4</a> |
   | WWW-Authenticate    | http     | standard | <a href="#section-4.1">Section 4.1</a> |
   +---------------------+----------+----------+-------------+

   The change controller is: "IETF (iesg@ietf.org) - Internet
   Engineering Task Force".




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<span class="h2"><a class="selflink" id="section-6" href="#section-6">6</a>.  Security Considerations</span>

   This section is meant to inform developers, information providers,
   and users of known security concerns specific to HTTP authentication.
   More general security considerations are addressed in HTTP messaging
   [<a href="./rfc7230" title="&quot;Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing&quot;">RFC7230</a>] and semantics [<a href="./rfc7231" title="&quot;Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content&quot;">RFC7231</a>].

   Everything about the topic of HTTP authentication is a security
   consideration, so the list of considerations below is not exhaustive.
   Furthermore, it is limited to security considerations regarding the
   authentication framework, in general, rather than discussing all of
   the potential considerations for specific authentication schemes
   (which ought to be documented in the specifications that define those
   schemes).  Various organizations maintain topical information and
   links to current research on Web application security (e.g.,
   [<a href="#ref-OWASP" title="&quot;A Guide to Building Secure Web Applications and Web Services&quot;">OWASP</a>]), including common pitfalls for implementing and using the
   authentication schemes found in practice.

<span class="h3"><a class="selflink" id="section-6.1" href="#section-6.1">6.1</a>.  Confidentiality of Credentials</span>

   The HTTP authentication framework does not define a single mechanism
   for maintaining the confidentiality of credentials; instead, each
   authentication scheme defines how the credentials are encoded prior
   to transmission.  While this provides flexibility for the development
   of future authentication schemes, it is inadequate for the protection
   of existing schemes that provide no confidentiality on their own, or
   that do not sufficiently protect against replay attacks.
   Furthermore, if the server expects credentials that are specific to
   each individual user, the exchange of those credentials will have the
   effect of identifying that user even if the content within
   credentials remains confidential.

   HTTP depends on the security properties of the underlying transport-
   or session-level connection to provide confidential transmission of
   header fields.  In other words, if a server limits access to
   authenticated users using this framework, the server needs to ensure
   that the connection is properly secured in accordance with the nature
   of the authentication scheme used.  For example, services that depend
   on individual user authentication often require a connection to be
   secured with TLS ("Transport Layer Security", [<a href="./rfc5246" title="&quot;The Transport Layer Security (TLS) Protocol Version 1.2&quot;">RFC5246</a>]) prior to
   exchanging any credentials.

<span class="h3"><a class="selflink" id="section-6.2" href="#section-6.2">6.2</a>.  Authentication Credentials and Idle Clients</span>

   Existing HTTP clients and user agents typically retain authentication
   information indefinitely.  HTTP does not provide a mechanism for the
   origin server to direct clients to discard these cached credentials,
   since the protocol has no awareness of how credentials are obtained



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   or managed by the user agent.  The mechanisms for expiring or
   revoking credentials can be specified as part of an authentication
   scheme definition.

   Circumstances under which credential caching can interfere with the
   application's security model include but are not limited to:

   o  Clients that have been idle for an extended period, following
      which the server might wish to cause the client to re-prompt the
      user for credentials.

   o  Applications that include a session termination indication (such
      as a "logout" or "commit" button on a page) after which the server
      side of the application "knows" that there is no further reason
      for the client to retain the credentials.

   User agents that cache credentials are encouraged to provide a
   readily accessible mechanism for discarding cached credentials under
   user control.

<span class="h3"><a class="selflink" id="section-6.3" href="#section-6.3">6.3</a>.  Protection Spaces</span>

   Authentication schemes that solely rely on the "realm" mechanism for
   establishing a protection space will expose credentials to all
   resources on an origin server.  Clients that have successfully made
   authenticated requests with a resource can use the same
   authentication credentials for other resources on the same origin
   server.  This makes it possible for a different resource to harvest
   authentication credentials for other resources.

   This is of particular concern when an origin server hosts resources
   for multiple parties under the same canonical root URI (<a href="#section-2.2">Section 2.2</a>).
   Possible mitigation strategies include restricting direct access to
   authentication credentials (i.e., not making the content of the
   Authorization request header field available), and separating
   protection spaces by using a different host name (or port number) for
   each party.














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<span class="h2"><a class="selflink" id="section-7" href="#section-7">7</a>.  Acknowledgments</span>

   This specification takes over the definition of the HTTP
   Authentication Framework, previously defined in <a href="./rfc2617">RFC 2617</a>.  We thank
   John Franks, Phillip M. Hallam-Baker, Jeffery L. Hostetler, Scott D.
   Lawrence, Paul J. Leach, Ari Luotonen, and Lawrence C. Stewart for
   their work on that specification.  See <a href="./rfc2617#section-6">Section&nbsp;6 of [RFC2617]</a> for
   further acknowledgements.

   See <a href="./rfc7230#section-10">Section&nbsp;10 of [RFC7230]</a> for the Acknowledgments related to this
   document revision.

<span class="h2"><a class="selflink" id="section-8" href="#section-8">8</a>.  References</span>

<span class="h3"><a class="selflink" id="section-8.1" href="#section-8.1">8.1</a>.  Normative References</span>

   [<a id="ref-RFC2119">RFC2119</a>]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", <a href="https://www.rfc-editor.org/bcp/bcp14">BCP 14</a>, <a href="./rfc2119">RFC 2119</a>, March 1997.

   [<a id="ref-RFC5234">RFC5234</a>]  Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", STD 68, <a href="./rfc5234">RFC 5234</a>, January 2008.

   [<a id="ref-RFC7230">RFC7230</a>]  Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
              Protocol (HTTP/1.1): Message Syntax and Routing",
              <a href="./rfc7230">RFC 7230</a>, June 2014.

   [<a id="ref-RFC7231">RFC7231</a>]  Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
              Protocol (HTTP/1.1): Semantics and Content", <a href="./rfc7231">RFC 7231</a>,
              June 2014.

   [<a id="ref-RFC7234">RFC7234</a>]  Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,
              Ed., "Hypertext Transfer Protocol (HTTP/1.1): Caching",
              <a href="./rfc7234">RFC 7234</a>, June 2014.

<span class="h3"><a class="selflink" id="section-8.2" href="#section-8.2">8.2</a>.  Informative References</span>

   [<a id="ref-BCP90">BCP90</a>]    Klyne, G., Nottingham, M., and J. Mogul, "Registration
              Procedures for Message Header Fields", <a href="https://www.rfc-editor.org/bcp/bcp90">BCP 90</a>, <a href="./rfc3864">RFC 3864</a>,
              September 2004.

   [<a id="ref-OWASP">OWASP</a>]    van der Stock, A., Ed., "A Guide to Building Secure Web
              Applications and Web Services", The Open Web Application
              Security Project (OWASP) 2.0.1, July 2005,
              &lt;<a href="https://www.owasp.org/">https://www.owasp.org/</a>&gt;.

   [<a id="ref-RFC2616">RFC2616</a>]  Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
              Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
              Transfer Protocol -- HTTP/1.1", <a href="./rfc2616">RFC 2616</a>, June 1999.



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   [<a id="ref-RFC2617">RFC2617</a>]  Franks, J., Hallam-Baker, P., Hostetler, J., Lawrence, S.,
              Leach, P., Luotonen, A., and L. Stewart, "HTTP
              Authentication: Basic and Digest Access Authentication",
              <a href="./rfc2617">RFC 2617</a>, June 1999.

   [<a id="ref-RFC3986">RFC3986</a>]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
              Resource Identifier (URI): Generic Syntax", STD 66,
              <a href="./rfc3986">RFC 3986</a>, January 2005.

   [<a id="ref-RFC4648">RFC4648</a>]  Josefsson, S., "The Base16, Base32, and Base64 Data
              Encodings", <a href="./rfc4648">RFC 4648</a>, October 2006.

   [<a id="ref-RFC5226">RFC5226</a>]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", <a href="https://www.rfc-editor.org/bcp/bcp26">BCP 26</a>, <a href="./rfc5226">RFC 5226</a>,
              May 2008.

   [<a id="ref-RFC5246">RFC5246</a>]  Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.2", <a href="./rfc5246">RFC 5246</a>, August 2008.

































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<span class="h2"><a class="selflink" id="appendix-A" href="#appendix-A">Appendix A</a>.  Changes from RFCs 2616 and 2617</span>

   The framework for HTTP Authentication is now defined by this
   document, rather than <a href="./rfc2617">RFC 2617</a>.

   The "realm" parameter is no longer always required on challenges;
   consequently, the ABNF allows challenges without any auth parameters.
   (<a href="#section-2">Section 2</a>)

   The "token68" alternative to auth-param lists has been added for
   consistency with legacy authentication schemes such as "Basic".
   (<a href="#section-2">Section 2</a>)

   This specification introduces the Authentication Scheme Registry,
   along with considerations for new authentication schemes.
   (<a href="#section-5.1">Section 5.1</a>)

<span class="h2"><a class="selflink" id="appendix-B" href="#appendix-B">Appendix B</a>.  Imported ABNF</span>

   The following core rules are included by reference, as defined in
   <a href="./rfc5234#appendix-B.1">Appendix&nbsp;B.1 of [RFC5234]</a>: ALPHA (letters), CR (carriage return),
   CRLF (CR LF), CTL (controls), DIGIT (decimal 0-9), DQUOTE (double
   quote), HEXDIG (hexadecimal 0-9/A-F/a-f), LF (line feed), OCTET (any
   8-bit sequence of data), SP (space), and VCHAR (any visible US-ASCII
   character).

   The rules below are defined in [<a href="./rfc7230" title="&quot;Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing&quot;">RFC7230</a>]:

     BWS           = &lt;BWS, see <a href="./rfc7230#section-3.2.3">[RFC7230], Section&nbsp;3.2.3</a>&gt;
     OWS           = &lt;OWS, see <a href="./rfc7230#section-3.2.3">[RFC7230], Section&nbsp;3.2.3</a>&gt;
     quoted-string = &lt;quoted-string, see <a href="./rfc7230#section-3.2.6">[RFC7230], Section&nbsp;3.2.6</a>&gt;
     token         = &lt;token, see <a href="./rfc7230#section-3.2.6">[RFC7230], Section&nbsp;3.2.6</a>&gt;



















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<span class="h2"><a class="selflink" id="appendix-C" href="#appendix-C">Appendix C</a>.  Collected ABNF</span>

   In the collected ABNF below, list rules are expanded as per <a href="./rfc7230#section-1.2">Section</a>
   <a href="./rfc7230#section-1.2">1.2 of [RFC7230]</a>.

   Authorization = credentials

   BWS = &lt;BWS, see <a href="./rfc7230#section-3.2.3">[RFC7230], Section&nbsp;3.2.3</a>&gt;

   OWS = &lt;OWS, see <a href="./rfc7230#section-3.2.3">[RFC7230], Section&nbsp;3.2.3</a>&gt;

   Proxy-Authenticate = *( "," OWS ) challenge *( OWS "," [ OWS
    challenge ] )
   Proxy-Authorization = credentials

   WWW-Authenticate = *( "," OWS ) challenge *( OWS "," [ OWS challenge
    ] )

   auth-param = token BWS "=" BWS ( token / quoted-string )
   auth-scheme = token

   challenge = auth-scheme [ 1*SP ( token68 / [ ( "," / auth-param ) *(
    OWS "," [ OWS auth-param ] ) ] ) ]
   credentials = auth-scheme [ 1*SP ( token68 / [ ( "," / auth-param )
    *( OWS "," [ OWS auth-param ] ) ] ) ]

   quoted-string = &lt;quoted-string, see <a href="./rfc7230#section-3.2.6">[RFC7230], Section&nbsp;3.2.6</a>&gt;

   token = &lt;token, see <a href="./rfc7230#section-3.2.6">[RFC7230], Section&nbsp;3.2.6</a>&gt;
   token68 = 1*( ALPHA / DIGIT / "-" / "." / "_" / "~" / "+" / "/" )
    *"="




















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Index

   4
      401 Unauthorized (status code)  6
      407 Proxy Authentication Required (status code)  6

   A
      Authorization header field  8

   C
      Canonical Root URI  5

   G
      Grammar
         auth-param  4
         auth-scheme  4
         Authorization  8
         challenge  4
         credentials  5
         Proxy-Authenticate  8
         Proxy-Authorization  9
         token68  4
         WWW-Authenticate  7

   P
      Protection Space  5
      Proxy-Authenticate header field  8
      Proxy-Authorization header field  9

   R
      Realm  5

   W
      WWW-Authenticate header field  7

















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Authors' Addresses

   Roy T. Fielding (editor)
   Adobe Systems Incorporated
   345 Park Ave
   San Jose, CA  95110
   USA

   EMail: fielding@gbiv.com
   URI:   <a href="http://roy.gbiv.com/">http://roy.gbiv.com/</a>


   Julian F. Reschke (editor)
   greenbytes GmbH
   Hafenweg 16
   Muenster, NW  48155
   Germany

   EMail: julian.reschke@greenbytes.de
   URI:   <a href="http://greenbytes.de/tech/webdav/">http://greenbytes.de/tech/webdav/</a>































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</pre>