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Versions: (draft-mills-kitten-sasl-oauth) 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22 23 RFC 7628

KITTEN                                                          W. Mills
Internet-Draft                                               Yahoo! Inc.
Intended status: Standards Track                            T. Showalter
Expires: June 18, 2014
                                                           H. Tschofenig
                                            Nokia Solutions and Networks
                                                       December 15, 2013


                   A set of SASL Mechanisms for OAuth
                  draft-ietf-kitten-sasl-oauth-12.txt

Abstract

   OAuth enables a third-party application to obtain limited access to a
   protected resource, either on behalf of a resource owner by
   orchestrating an approval interaction, or by allowing the third-party
   application to obtain access on its own behalf.

   This document defines how an application client uses credentials
   obtained via OAuth over the Simple Authentication and Security Layer
   (SASL) to access a protected resource at a resource serve.  Thereby,
   it enables schemes defined within the OAuth framework for non-HTTP-
   based application protocols.

   Clients typically store the user's long-term credential.  This does,
   however, lead to significant security vulnerabilities, for example,
   when such a credential leaks.  A significant benefit of OAuth for
   usage in those clients is that the password is replaced by a shared
   secret with higher entropy, i.e., the token.  Tokens typically
   provide limited access rights and can be managed and revoked
   separately from the user's long-term password.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."




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   This Internet-Draft will expire on June 18, 2014.

Copyright Notice

   Copyright (c) 2013 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) 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.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   5
   3.  OAuth SASL Mechanism Specifications . . . . . . . . . . . . .   6
     3.1.  Initial Client Response . . . . . . . . . . . . . . . . .   7
       3.1.1.  Reserved Key/Values . . . . . . . . . . . . . . . . .   7
     3.2.  Server's Response . . . . . . . . . . . . . . . . . . . .   8
       3.2.1.  OAuth Identifiers in the SASL Context . . . . . . . .   8
       3.2.2.  Server Response to Failed Authentication  . . . . . .   8
       3.2.3.  Completing an Error Message Sequence  . . . . . . . .   9
     3.3.  OAuth Access Token Types using Keyed Message Digests  . .   9
   4.  Examples  . . . . . . . . . . . . . . . . . . . . . . . . . .  10
     4.1.  Successful Bearer Token Exchange  . . . . . . . . . . . .  11
     4.2.  Failed Exchange . . . . . . . . . . . . . . . . . . . . .  11
     4.3.  SMTP Example of a Failed Negotiation  . . . . . . . . . .  12
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .  13
   6.  Internationalization Considerations . . . . . . . . . . . . .  14
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  14
     7.1.  SASL Registration . . . . . . . . . . . . . . . . . . . .  14
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  15
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .  15
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  16
   Appendix A.  Acknowlegements  . . . . . . . . . . . . . . . . . .  16
   Appendix B.  Document History . . . . . . . . . . . . . . . . . .  16
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  19

1.  Introduction

   OAuth 1.0a [RFC5849] and OAuth 2.0 [RFC6749] are protocol frameworks
   that enable a third-party application to obtain limited access to a



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   protected resource, either on behalf of a resource owner by
   orchestrating an approval interaction, or by allowing the third-party
   application to obtain access on its own behalf.

   The core OAuth 2.0 specification [RFC6749] specifies the interaction
   between the OAuth client and the authorization server; it does not
   define the interaction between the OAuth client and the resource
   server for the access to a protected resource using an Access Token.
   Instead, the OAuth client to resource server interaction is described
   in separate specifications, such as the bearer token specification
   [RFC6750] and the MAC Token specification
   [I-D.ietf-oauth-v2-http-mac].  OAuth 1.0a included the protocol
   specification for the communication between the OAuth client and the
   resource server in [RFC5849].

   The main use cases for OAuth 2.0 and OAuth 1.0a have so far focused
   on an HTTP-based environment only.  This document integrates OAuth
   1.0a and OAuth 2.0 into non-HTTP-based applications using the
   integration into SASL.  Hence, this document takes advantage of the
   OAuth protocol and its deployment base to provide a way to use the
   Simple Authentication and Security Layer (SASL) [RFC4422] to gain
   access to resources when using non-HTTP-based protocols, such as the
   Internet Message Access Protocol (IMAP) [RFC3501] and SMTP [RFC5321],
   which is what this memo uses in the examples.

   To illustrate the impact of integrating this specification into an
   OAuth-enabled application environment Figure 1 shows the abstract
   message flow of OAuth 2.0 [RFC6749].  As indicated in the figure,
   this document impacts the exchange of messages (E) and (F) since SASL
   is used for interaction between the client and the resource server
   instead of HTTP.




















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                                                              ----+
   +--------+                                  +---------------+  |
   |        |--(A)-- Authorization Request --->|   Resource    |  |
   |        |                                  |     Owner     |  |Plain
   |        |<-(B)------ Access Grant ---------|               |  |OAuth
   |        |                                  +---------------+  |2.0
   |        |                                                     |
   |        |         Client Credentials &     +---------------+  |
   |        |--(C)------ Access Grant -------->| Authorization |  |
   | Client |                                  |     Server    |  |
   |        |<-(D)------ Access Token ---------|               |  |
   |        |      (w/ Optional Refresh Token) +---------------+  |
   |        |                                                 ----+
   |        |                                                 ----+
   |        |                                  +---------------+  |
   |        |                                  |               |  |OAuth
   |        |--(E)------ Access Token -------->|    Resource   |  |over
   |        |                                  |     Server    |  |SASL
   |        |<-(F)---- Protected Resource -----|               |  |
   |        |                                  |               |  |
   +--------+                                  +---------------+  |
                                                              ----+

                     Figure 1: OAuth 2.0 Protocol Flow

   The Simple Authentication and Security Layer (SASL) is a framework
   for providing authentication and data security services in
   connection-oriented protocols via replaceable authentication
   mechanisms.  It provides a structured interface between protocols and
   mechanisms.  The resulting framework allows new protocols to reuse
   existing authentication protocols and allows old protocols to make
   use of new authentication mechanisms.  The framework also provides a
   protocol for securing subsequent protocol exchanges within a data
   security layer.

   When OAuth is integrated into SASL the high-level steps are as
   follows:

      (A) The client requests authorization from the resource owner.
      The authorization request can be made directly to the resource
      owner (as shown), or preferably indirectly via the authorization
      server as an intermediary.









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      (B) The client receives an authorization grant which is a
      credential representing the resource owner's authorization,
      expressed using one of four grant types defined in this
      specification or using an extension grant type.  The authorization
      grant type depends on the method used by the client to request
      authorization and the types supported by the authorization server.

      (C) The client requests an access token by authenticating with the
      authorization server and presenting the authorization grant.

      (D) The authorization server authenticates the client and
      validates the authorization grant, and if valid issues an access
      token.

      (E) The client requests the protected resource from the resource
      server and authenticates by presenting the access token.

      (F) The resource server validates the access token, and if valid,
      indicates a successful authentication.

   Again, steps (E) and (F) are not defined in [RFC6749] (but are
   described in, for example, [RFC6750] for the OAuth Bearer Token
   instead) and are the main functionality specified within this
   document.  Consequently, the message exchange shown in Figure 1 is
   the result of this specification.  The client will generally need to
   determine the authentication endpoints (and perhaps the service
   endpoints) before the OAuth 2.0 protocol exchange messages in steps
   (A)-(D) are executed.  The discovery of the resource owner and
   authorization server endpoints is outside the scope of this
   specification.  The client must discover those endpoints using a
   discovery mechanisms, such as Webfinger using host-meta [RFC7033].
   In band discovery is not tenable if clients support the OAuth 2.0
   password grant.  Once credentials are obtained the client proceeds to
   steps (E) and (F) defined in this specification.

   OAuth 1.0 follows a similar model but uses a different terminology
   and does not separate the resource server from the authorization
   server.

2.  Terminology

   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 [RFC2119].

   The reader is assumed to be familiar with the terms used in the OAuth
   2.0 specification [RFC6749].




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   In examples, "C:" and "S:" indicate lines sent by the client and
   server respectively.  Line breaks have been inserted for readability.

   Note that the IMAP SASL specification requires base64 encoding, see
   Section 4 of [RFC4648], not this memo.

3.  OAuth SASL Mechanism Specifications

   SASL is used as an authentication framework in a variety of
   application layer protocols.  This document defines the following
   SASL mechanisms for usage with OAuth:



      OAUTHBEARER:  OAuth 2.0 bearer tokens, as described in [RFC6750].
         RFC 6750 uses Transport Layer Security (TLS) to secure the
         protocol interaction between the client and the resource
         server.

      OAUTH10A:  OAuth 1.0a MAC tokens (using the HMAC-SHA1 keyed
         message digest), as described in Section 3.4.2 of [RFC5849].

   New extensions may be defined to add additional OAuth Access Token
   Types.  Such a new SASL OAuth mechanism can be added by simply
   registering the new name(s) and citing this specification for the
   further definition.

   These mechanisms are client initiated and lock-step, the server
   always replying to a client message.  In the case where the client
   has and correctly uses a valid token the flow is:

   o  Client sends a valid and correct initial client response.

   o  Server responds with a successful authentication.

   In the case where authorization fails the server sends an error
   result, then client MUST then send an additional message to the
   server in order to allow the server to finish the exchange.  Some
   protocols and common SASL implementations do not support both sending
   a SASL message and finalizing a SASL negotiation, the additional
   client message in the error case deals with this problem.  This
   exchange is:

   o  Client sends an invalid initial client response.

   o  Server responds with an error message.

   o  Client sends a dummy client response.



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   o  Server fails the authentication.

3.1.  Initial Client Response

   Client responses are a key/value pair sequence.  These key/value
   pairs carry the equivalent values from an HTTP context in order to be
   able to complete an OAuth style HTTP authorization.  Unknown key/
   value pairs MUST be ignored by the server.  The ABNF [RFC5234] syntax
   is:


     kvsep          = %x01
     key            = 1*ALPHA
     value          = *(VCHAR / SP / HTAB / CR / LF )
     kvpair         = key "=" value kvsep
     client_resp    = 0*kvpair kvsep

   The following key/value pairs are defined in the client response:



      auth (REQUIRED):  The payload of the HTTP Authorization header for
         an equivalent HTTP OAuth authorization.

      host:  Contains the host name to which the client connected.

      port:  Contains the port number represented as a decimal positive
         integer string without leading zeros to which the client
         connected.

      qs:  The HTTP query string.  This is reserved for future use, the
         client SHOUD NOT send it, and has the default value of "".

   For OAuth token types that use keyed message digests the client MUST
   send host and port number key/values, and the server MUST fail an
   authorization request requiring keyed message digests that do not
   have host and port values.  In OAuth 1.0a for example, the so-called
   "signature base string calculation" includes the reconstructed HTTP
   URL.

3.1.1.  Reserved Key/Values










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   In these mechanisms values for path, query string and post body are
   assigned default values.  OAuth authorization schemes MAY define
   usage of these in the SASL context and extend this specification.
   For OAuth Access Token Types that use request keyed message digest
   the default values MUST be used unless explicit values are provided
   in the client response.  The following key values are reserved for
   future use:



      mthd (RESERVED):  HTTP method, the default value is "POST".

      path (RESERVED):  HTTP path data, the default value is "/".

      post (RESERVED):  HTTP post data, the default value is "".

3.2.  Server's Response

   The server validates the response per the specification for the OAuth
   Access Token Types used.  If the OAuth Access Token Type utilizes a
   keyed message digest of the request parameters then the client must
   provide a client response that satisfies the data requirements for
   the scheme in use.

   The server responds to a successfully verified client message by
   completing the SASL negotiation.  The authenticated identity reported
   by the SASL mechanism is the identity securely established for the
   client with the OAuth credential.  The application, not the SASL
   mechanism, based on local access policy determines whether the
   identity reported by the mechanism is allowed access to the requested
   resource.  Note that the semantics of the authz-id is specified by
   the SASL framework [RFC4422].

3.2.1.  OAuth Identifiers in the SASL Context

   In the OAuth framework the client may be authenticated by the
   authorization server and the resource owner is authenticated to the
   authorization server.  OAuth access tokens may contain information
   about the authentication of the resource owner and about the client
   and may therefore make this information accessible to the resource
   server.

   If both identifiers are needed by an application the developer will
   need to provide a way to communicate that from the SASL mechanism
   back to the application.

3.2.2.  Server Response to Failed Authentication




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   For a failed authentication the server returns a JSON [RFC4627]
   formatted error result, and fails the authentication.  The error
   result consists of the following values:



      status (REQUIRED):  The authorization error code.  Valid error
         codes are defined in the IANA [[need registry name]] registry
         specified in the OAuth 2 core specification.

      scope (OPTIONAL):  An OAuth scope which is valid to access the
         service.  This may be empty which implies that unscoped tokens
         are required, or a space separated list.  Use of a space
         separated list is NOT RECOMMENDED.

   If the resource server provides a scope then the client MUST always
   request scoped tokens from the token endpoint.  If the resource
   server provides no scope to the client then the client SHOULD presume
   an empty scope (unscoped token) is needed.

   If channel binding is in use and the channel binding fails the server
   responds with a status code set to 412 to indicate that the channel
   binding precondition failed.  If the authentication scheme in use
   does not include signing the server SHOULD revoke the presented
   credential and the client SHOULD discard that credential.

3.2.3.  Completing an Error Message Sequence

   Section 3.6 of [RFC4422] explicitly prohibits additional information
   in an unsuccessful authentication outcome.  Therefore, the error
   message is sent in a normal message.  The client MUST then send an
   additional client response consisting of a single %x01 (control A)
   character to the server in order to allow the server to finish the
   exchange.

3.3.  OAuth Access Token Types using Keyed Message Digests

   OAuth Access Token Types may use keyed message digests and the client
   and the resource server may need to perform a cryptographic
   computation for integrity protection and data origin authentication.

   OAuth is designed for access to resources identified by URIs.  SASL
   is designed for user authentication, and has no facility for more
   fine-grained access control.  In this specification we require or
   define default values for the data elements from an HTTP request
   which allow the signature base string to be constructed properly.
   The default HTTP path is "/" and the default post body is empty.
   These atoms are defined as extension points so that no changes are



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   needed if there is a revision of SASL which supports more specific
   resource authorization, e.g., IMAP access to a specific folder or FTP
   access limited to a specific directory.

   Using the example in the OAuth 1.0a specification as a starting
   point, on an IMAP server running on port 143 and given the OAuth 1.0a
   style authorization request (with %x01 shown as ^A and line breaks
   added for readability) below:

   n,a=user@example.com^A
   host=example.com^A
   user=user@example.com^A
   port=143^A
   auth=OAuth realm="Example",
              oauth_consumer_key="9djdj82h48djs9d2",
              oauth_token="kkk9d7dh3k39sjv7",
              oauth_signature_method="HMAC-SHA1",
              oauth_timestamp="137131201",
              oauth_nonce="7d8f3e4a",
              oauth_signature="Tm90IGEgcmVhbCBzaWduYXR1cmU%3D"^A^A

   The signature base string would be constructed per the OAuth 1.0
   specification [RFC5849] with the following things noted:

   o  The method value is defaulted to POST.

   o  The scheme defaults to be "http", and any port number other than
      80 is included.

   o  The path defaults to "/".

   o  The query string defaults to "".

   In this example the signature base string with line breaks added for
   readability would be:

   POST&http%3A%2F%2Fexample.com:143%2F&oauth_consumer_key%3D9djdj82h4
   8djs9d2%26oauth_nonce%3D7d8f3e4a%26oauth_signature_method%3DHMAC-SH
   A1%26oauth_timestamp%3D137131201%26oauth_token%3Dkkk9d7dh3k39sjv7

4.  Examples

   These examples illustrate exchanges between an IMAP and SMTP clients
   and servers.

   Note to implementers: The SASL OAuth method names are case
   insensitive.  One example uses "Bearer" but that could as easily be
   "bearer", "BEARER", or "BeArEr".



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4.1.  Successful Bearer Token Exchange

   This example shows a successful OAuth 2.0 bearer token exchange.
   Note that line breaks are inserted for readability and the underlying
   TLS establishment is not shown either.

   S: * OK IMAP4rev1 Server Ready
   C: t0 CAPABILITY
   S: * CAPABILITY IMAP4rev1 AUTH=OAUTHBEARER SASL-IR
   S: t0 OK Completed
   C: t1 AUTHENTICATE OAUTHBEARER bixhPXVzZXJAZXhhbXBsZS5jb20BaG9zdD1zZX
         J2ZXIuZXhhbXBsZS5jb20BcG9ydD0xNDMBYXV0aD1CZWFyZXIgdkY5ZGZ0NHFtV
         GMyTnZiM1JsY2tCaGJIUmhkbWx6ZEdFdVkyOXRDZz09AQE=
   S: t1 OK SASL authentication succeeded

   As required by IMAP [RFC3501], the payloads are base64-encoded.  The
   decoded initial client response (with %x01 represented as ^A and long
   lines wrapped for readability) is:

   n,a=user@example.com^Ahost=server.example.com^Aport=143^A
   auth=Bearer vF9dft4qmTc2Nvb3RlckBhbHRhdmlzdGEuY29tCg==^A^A

   The same credential used in an SMTP exchange is shown below.  Note
   that line breaks are inserted for readability, and that the SMTP
   protocol terminates lines with CR and LF characters (ASCII values
   0x0D and 0x0A), these are not displayed explicitly in the example.

   [connection begins]
   S: 220 mx.example.com ESMTP 12sm2095603fks.9
   C: EHLO sender.example.com
   S: 250-mx.example.com at your service,[172.31.135.47]
   S: 250-SIZE 35651584
   S: 250-8BITMIME
   S: 250-AUTH LOGIN PLAIN OAUTHBEARER
   S: 250-ENHANCEDSTATUSCODES
   S: 250 PIPELINING
   C: t1 AUTHENTICATE OAUTHBEARER bixhPXVzZXJAZXhhbXBsZS5jb20BaG9zdD1zZX
         J2ZXIuZXhhbXBsZS5jb20BcG9ydD0xNDMBYXV0aD1CZWFyZXIgdkY5ZGZ0NHFtV
         GMyTnZiM1JsY2tCaGJIUmhkbWx6ZEdFdVkyOXRDZz09AQE=
   S: 235 Authentication successful.
   [connection continues...]

4.2.  Failed Exchange

   This example shows a failed exchange because of the empty
   Authorization header, which is how a client can query for the needed
   scope.  Note that line breaks are inserted for readability.




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   S: * CAPABILITY IMAP4rev1 AUTH=OAUTHBEARER SASL-IR IMAP4rev1 Server
        Ready
   S: t0 OK Completed
   C: t1 AUTHENTICATE OAUTHBEARER cD10bHMtdW5pcXVlLGE9dXNlckBleGFtcG
         xlLmNvbQFob3N0PXNlcnZlci5leGFtcGxlLmNvbQFwb3J0PTE0MwFhdXRoP
         QFjYmRhdGE9AQE=
   S: + ewoic3RhdHVzIjoiNDAxIgoic2NvcGUiOiJleGFtcGxlX3Njb3BlIgp9
   C: + AQ==
   S: t1 NO SASL authentication failed

   The decoded initial client response is:

   n,a=user@example.com,^Ahost=server.example.com^A
   port=143^Aauth=^A^A

   The decoded server error response is:

   {
   "status":"401",
   "scope":"example_scope"
   }

   The client responds with the required dummy response.

4.3.  SMTP Example of a Failed Negotiation

   This example shows an authorization failure in an SMTP exchange.
   Note that line breaks are inserted for readability, and that the SMTP
   protocol terminates lines with CR and LF characters (ASCII values
   0x0D and 0x0A), these are not displayed explicitly in the example.

[connection begins]
S: 220 mx.example.com ESMTP 12sm2095603fks.9
C: EHLO sender.example.com
S: 250-mx.example.com at your service,[172.31.135.47]
S: 250-SIZE 35651584
S: 250-8BITMIME
S: 250-AUTH LOGIN PLAIN OAUTHBEARER
S: 250-ENHANCEDSTATUSCODES
S: 250 PIPELINING
C: AUTH OAUTHBEARER bixhPT1zb21ldXNlckBleGFtcGxlLmNvbQFhdXRoPUJlYXJlciB2
       RjlkZnQ0cW1UYzJOdmIzUmxja0JoZEhSaGRtbHpkR0V1WTI5dENnPT0BAQ==
S: 334 eyJzdGF0dXMiOiI0MDEiLCJzY2hlbWVzIjoiYmVhcmVyIG1hYyIsInNjb3BlIjoia
       HR0cHM6Ly9tYWlsLmdvb2dsZS5jb20vIn0K
C: AQ==
S: 535-5.7.1 Username and Password not accepted. Learn more at
S: 535 5.7.1 http://support.example.com/mail/oauth
[connection continues...]



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   The server returned an error message in the 334 SASL message, the
   client responds with the required dummy response, and the server
   finalizes the negotiation.

5.  Security Considerations

   OAuth 1.0a and OAuth 2 allows for a variety of deployment scenarios,
   and the security properties of these profiles vary.  As shown in
   Figure 1 this specification is aimed to be integrated into a larger
   OAuth deployment.  Application developers therefore need to
   understand the needs of their security requirements based on a threat
   assessment before selecting a specific SASL OAuth mechanism.  For
   OAuth 2.0 a detailed security document [RFC6819] provides guidance to
   select those OAuth 2.0 components that help to mitigate threats for a
   given deployment.  For OAuth 1.0a Section 4 of RFC 5849 [RFC5849]
   provides guidance specific to OAuth 1.0.

   This document specifies three SASL Mechanisms for OAuth and each
   comes with different security properties.

   OAUTHBEARER:  This mechanism borrows from OAuth 2.0 bearer tokens
      [RFC6750].  It relies on the application using TLS to protect the
      OAuth 2.0 Bearer Token exchange; without TLS usage at the
      application layer this method is completely insecure.
      Consequently, TLS MUST be provided by the application when
      choosing this authentication mechanism.

   OAUTH10A:  This mechanism re-uses OAuth 1.0a MAC tokens (using the
      HMAC-SHA1 keyed message digest), as described in Section 3.4.2 of
      [RFC5849].  To compute the keyed message digest in the same way
      was in RFC 5839 this specification conveys additional parameters
      between the client and the server.  This SASL mechanism only
      supports client authentication.  If server-side authentication is
      desireable then it must be provided by the application underneath
      the SASL layer.  The use of TLS is strongly RECOMMENDED.

   Additionally, the following aspects are worth pointing out:

   An access token is not equivalent to the user's long term password.

      Care has to be taken when these OAuth credentials are used for
      actions like changing passwords (as it is possible with some
      protocols, e.g., XMPP).  The resource server should ensure that
      actions taken in the authenticated channel are appropriate to the
      strength of the presented credential.

   Lifetime of the appliation sessions.




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      It is possible that SASL will be authenticating a connection and
      the life of that connection may outlast the life of the access
      token used to establish it.  This is a common problem in
      application protocols where connections are long-lived, and not a
      problem with this mechanism per se.  Resource servers may
      unilaterally disconnect clients in accordance with the application
      protocol.

   Access tokens have a lifetime.

      Reducing the lifetime of an access token provides security
      benefits and OAuth 2.0 introduces refresh tokens to obtain new
      access token on the fly without any need for a human interaction.
      Additionally, a previously obtained access token may be revoked or
      rendered invalid at any time by the authorization server.  The
      client may request a new access token for each connection to a
      resource server, but it should cache and re-use valid credentials.

6.  Internationalization Considerations

   The identifer asserted by the OAuth authorization server about the
   resource owner inside the access token may be displayed to a human.
   For example, when SASL is used in the context of IMAP the resource
   server may assert the resource owner's email address to the IMAP
   server for usage in an email-based application.  The identifier may
   therefore contain internationalized characters and an application
   needs to ensure that the mapping between the identifier provided by
   OAuth is suitable for use with the application layer protocol SASL is
   incorporated into.

   At the time of writing the standardization of the various claims in
   the access token (in JSON format) is still ongoing, see
   [I-D.ietf-oauth-json-web-token].  Once completed it will provide a
   standardized format for exchanging identity information between the
   authorization server and the resource server.

7.  IANA Considerations

7.1.  SASL Registration

   The IANA is requested to register the following SASL profile:

      SASL mechanism profile: OAUTHBEARER

      Security Considerations: See this document

      Published Specification: See this document




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      For further information: Contact the authors of this document.

      Owner/Change controller: the IETF

      Note: None

   The IANA is requested to register the following SASL profile:

      SASL mechanism profile: OAUTH10A

      Security Considerations: See this document

      Published Specification: See this document

      For further information: Contact the authors of this document.

      Owner/Change controller: the IETF

      Note: None

8.  References

8.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC3174]  Eastlake, D. and P. Jones, "US Secure Hash Algorithm 1
              (SHA1)", RFC 3174, September 2001.

   [RFC4422]  Melnikov, A. and K. Zeilenga, "Simple Authentication and
              Security Layer (SASL)", RFC 4422, June 2006.

   [RFC4627]  Crockford, D., "The application/json Media Type for
              JavaScript Object Notation (JSON)", RFC 4627, July 2006.

   [RFC4648]  Josefsson, S., "The Base16, Base32, and Base64 Data
              Encodings", RFC 4648, October 2006.

   [RFC5056]  Williams, N., "On the Use of Channel Bindings to Secure
              Channels", RFC 5056, November 2007.

   [RFC5234]  Crocker, D. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", STD 68, RFC 5234, January 2008.

   [RFC5246]  Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.2", RFC 5246, August 2008.




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   [RFC5849]  Hammer-Lahav, E., "The OAuth 1.0 Protocol", RFC 5849,
              April 2010.

   [RFC6749]  Hardt, D., "The OAuth 2.0 Authorization Framework", RFC
              6749, October 2012.

   [RFC6750]  Jones, M. and D. Hardt, "The OAuth 2.0 Authorization
              Framework: Bearer Token Usage", RFC 6750, October 2012.

8.2.  Informative References

   [I-D.ietf-oauth-json-web-token]
              Jones, M., Bradley, J., and N. Sakimura, "JSON Web Token
              (JWT)", draft-ietf-oauth-json-web-token-13 (work in
              progress), November 2013.

   [I-D.ietf-oauth-v2-http-mac]
              Richer, J., Mills, W., Tschofenig, H., and P. Hunt, "OAuth
              2.0 Message Authentication Code (MAC) Tokens", draft-ietf-
              oauth-v2-http-mac-04 (work in progress), July 2013.

   [RFC3501]  Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION
              4rev1", RFC 3501, March 2003.

   [RFC5321]  Klensin, J., "Simple Mail Transfer Protocol", RFC 5321,
              October 2008.

   [RFC6819]  Lodderstedt, T., McGloin, M., and P. Hunt, "OAuth 2.0
              Threat Model and Security Considerations", RFC 6819,
              January 2013.

   [RFC7033]  Jones, P., Salgueiro, G., Jones, M., and J. Smarr,
              "WebFinger", RFC 7033, September 2013.

Appendix A.  Acknowlegements

   The authors would like to thank the members of the Kitten working
   group, and in addition and specifically: Simon Josefson, Torsten
   Lodderstadt, Ryan Troll, Alexey Melnikov, Jeffrey Hutzelman, and Nico
   Williams.

   This document was produced under the chairmanship of Alexey Melnikov,
   Tom Yu, Shawn Emery, Josh Howlett, Sam Hartman.  The supervising area
   directors was Stephen Farrell.

Appendix B.  Document History

   [[ to be removed by RFC editor before publication as an RFC ]]



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   -12

   o  Removed -PLUS components from the specification.

   -11

   o  Removed GSS-API components from the specification.

   o  Updated security consideration section.

   -10

   o  Clarifications throughout the document in response to the feedback
      from Jeffrey Hutzelman.

   -09

   o  Incorporated review by Alexey and Hannes.

   o  Clarified the three OAuth SASL mechanisms.

   o  Updated references

   o  Extended acknowledgements

   -08

   o  Fixed the channel binding examples for p=$cbtype

   o  More tuning of the authcid language and edited and renamed 3.2.1.

   -07

   o  Struck the MUST langiage from authzid.

   o

   -06

   o  Removed the user field.  Fixed the examples again.

   o  Added canonicalization language.

   o

   -05

   o  Fixed the GS2 header language again.



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   o  Separated out different OAuth schemes into different SASL
      mechanisms.  Took out the scheme in the error return.  Tuned up
      the IANA registrations.

   o  Added the user field back into the SASL message.

   o  Fixed the examples (again).

   o

   -04

   o  Changed user field to be carried in the gs2-header, and made gs2
      header explicit in all cases.

   o  Converted MAC examples to OAuth 1.0a.  Moved MAC to an informative
      reference.

   o  Changed to sending an empty client response (single control-A) as
      the second message of a failed sequence.

   o  Fixed channel binding prose to refer to the normative specs and
      removed the hashing of large channel binding data, which brought
      mroe problems than it solved.

   o  Added a SMTP examples for Bearer use case.

   -03

   o  Added user field into examples and fixed egregious errors there as
      well.

   o  Added text reminding developers that Authorization scheme names
      are case insensitive.

   -02

   o  Added the user data element back in.

   o  Minor editorial changes.

   -01

   o  Ripping out discovery.  Changed to refer to I-D.jones-appsawg-
      webfinger instead of WF and SWD older drafts.

   o  Replacing HTTP as the message format and adjusted all examples.




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   -00

   o  Renamed draft into proper IETF naming format now that it's
      adopted.

   o  Minor fixes.

Authors' Addresses

   William Mills
   Yahoo! Inc.

   Email: wmills_92105@yahoo.com


   Tim Showalter

   Email: tjs@psaux.com


   Hannes Tschofenig
   Nokia Solutions and Networks
   Linnoitustie 6
   Espoo  02600
   Finland

   Phone: +358 (50) 4871445
   Email: Hannes.Tschofenig@gmx.net
   URI:   http://www.tschofenig.priv.at






















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