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|
package sasl
import (
"bytes"
"encoding/json"
"errors"
"fmt"
"strconv"
"strings"
)
// The OAUTHBEARER mechanism name.
const OAuthBearer = "OAUTHBEARER"
type OAuthBearerError struct {
Status string `json:"status"`
Schemes string `json:"schemes"`
Scope string `json:"scope"`
}
type OAuthBearerOptions struct {
Username string
Token string
Host string
Port int
}
// Implements error
func (err *OAuthBearerError) Error() string {
return fmt.Sprintf("OAUTHBEARER authentication error (%v)", err.Status)
}
type oauthBearerClient struct {
OAuthBearerOptions
}
func (a *oauthBearerClient) Start() (mech string, ir []byte, err error) {
var authzid string
if a.Username != "" {
authzid = "a=" + a.Username
}
str := "n," + authzid + ","
if a.Host != "" {
str += "\x01host=" + a.Host
}
if a.Port != 0 {
str += "\x01port=" + strconv.Itoa(a.Port)
}
str += "\x01auth=Bearer " + a.Token + "\x01\x01"
ir = []byte(str)
return OAuthBearer, ir, nil
}
func (a *oauthBearerClient) Next(challenge []byte) ([]byte, error) {
authBearerErr := &OAuthBearerError{}
if err := json.Unmarshal(challenge, authBearerErr); err != nil {
return nil, err
} else {
return nil, authBearerErr
}
}
// An implementation of the OAUTHBEARER authentication mechanism, as
// described in RFC 7628.
func NewOAuthBearerClient(opt *OAuthBearerOptions) Client {
return &oauthBearerClient{*opt}
}
type OAuthBearerAuthenticator func(opts OAuthBearerOptions) *OAuthBearerError
type oauthBearerServer struct {
done bool
failErr error
authenticate OAuthBearerAuthenticator
}
func (a *oauthBearerServer) fail(descr string) ([]byte, bool, error) {
blob, err := json.Marshal(OAuthBearerError{
Status: "invalid_request",
Schemes: "bearer",
})
if err != nil {
panic(err) // wtf
}
a.failErr = errors.New(descr)
return blob, false, nil
}
func (a *oauthBearerServer) Next(response []byte) (challenge []byte, done bool, err error) {
// Per RFC, we cannot just send an error, we need to return JSON-structured
// value as a challenge and then after getting dummy response from the
// client stop the exchange.
if a.failErr != nil {
// Server libraries (go-smtp, go-imap) will not call Next on
// protocol-specific SASL cancel response ('*'). However, GS2 (and
// indirectly OAUTHBEARER) defines a protocol-independent way to do so
// using 0x01.
if len(response) != 1 && response[0] != 0x01 {
return nil, true, errors.New("unexpected response")
}
return nil, true, a.failErr
}
if a.done {
err = ErrUnexpectedClientResponse
return
}
// Generate empty challenge.
if response == nil {
return []byte{}, false, nil
}
a.done = true
// Cut n,a=username,\x01host=...\x01auth=...
// into
// n
// a=username
// \x01host=...\x01auth=...\x01\x01
parts := bytes.SplitN(response, []byte{','}, 3)
if len(parts) != 3 {
return a.fail("Invalid response")
}
flag := parts[0]
authzid := parts[1]
if !bytes.Equal(flag, []byte{'n'}) {
return a.fail("Invalid response, missing 'n' in gs2-cb-flag")
}
opts := OAuthBearerOptions{}
if len(authzid) > 0 {
if !bytes.HasPrefix(authzid, []byte("a=")) {
return a.fail("Invalid response, missing 'a=' in gs2-authzid")
}
opts.Username = string(bytes.TrimPrefix(authzid, []byte("a=")))
}
// Cut \x01host=...\x01auth=...\x01\x01
// into
// *empty*
// host=...
// auth=...
// *empty*
//
// Note that this code does not do a lot of checks to make sure the input
// follows the exact format specified by RFC.
params := bytes.Split(parts[2], []byte{0x01})
for _, p := range params {
// Skip empty fields (one at start and end).
if len(p) == 0 {
continue
}
pParts := bytes.SplitN(p, []byte{'='}, 2)
if len(pParts) != 2 {
return a.fail("Invalid response, missing '='")
}
switch string(pParts[0]) {
case "host":
opts.Host = string(pParts[1])
case "port":
port, err := strconv.ParseUint(string(pParts[1]), 10, 16)
if err != nil {
return a.fail("Invalid response, malformed 'port' value")
}
opts.Port = int(port)
case "auth":
const prefix = "bearer "
strValue := string(pParts[1])
// Token type is case-insensitive.
if !strings.HasPrefix(strings.ToLower(strValue), prefix) {
return a.fail("Unsupported token type")
}
opts.Token = strValue[len(prefix):]
default:
return a.fail("Invalid response, unknown parameter: " + string(pParts[0]))
}
}
authzErr := a.authenticate(opts)
if authzErr != nil {
blob, err := json.Marshal(authzErr)
if err != nil {
panic(err) // wtf
}
a.failErr = authzErr
return blob, false, nil
}
return nil, true, nil
}
func NewOAuthBearerServer(auth OAuthBearerAuthenticator) Server {
return &oauthBearerServer{authenticate: auth}
}
|
