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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: August 28, 2013
                                                           H. Tschofenig
                                                  Nokia Siemens Networks
                                                       February 24, 2013


             A set of SASL and GSS-API Mechanisms for OAuth
                  draft-ietf-kitten-sasl-oauth-10.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) or the Generic Security Service Application Program Interface
   (GSS-API) 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 token.
   Tokens typically provided limited access rights and can be managed
   and revoked separately from the user's long-term credential
   (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 August 28, 2013.

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.



































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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  7
   3.  OAuth SASL Mechanism Specifications  . . . . . . . . . . . . .  8
     3.1.  Initial Client Response  . . . . . . . . . . . . . . . . .  9
       3.1.1.  Reserved Key/Values  . . . . . . . . . . . . . . . . . 10
       3.1.2.  Use of the gs2-header  . . . . . . . . . . . . . . . . 10
     3.2.  Server's Response  . . . . . . . . . . . . . . . . . . . . 10
       3.2.1.  OAuth Identifiers in the SASL Context  . . . . . . . . 11
       3.2.2.  Server Response to Failed Authentication . . . . . . . 11
       3.2.3.  Completing an Error Message Sequence . . . . . . . . . 12
     3.3.  OAuth Access Token Types using Keyed Message Digests . . . 12
     3.4.  Channel Binding  . . . . . . . . . . . . . . . . . . . . . 13
   4.  GSS-API OAuth Mechanism Specification  . . . . . . . . . . . . 14
   5.  Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
     5.1.  Successful Bearer Token Exchange . . . . . . . . . . . . . 16
     5.2.  OAuth 1.0a Authorization with Channel Binding  . . . . . . 17
     5.3.  Failed Exchange  . . . . . . . . . . . . . . . . . . . . . 18
     5.4.  Failed Channel Binding . . . . . . . . . . . . . . . . . . 19
     5.5.  SMTP Example of a Failed Negotiation . . . . . . . . . . . 19
   6.  Security Considerations  . . . . . . . . . . . . . . . . . . . 21
   7.  Internationalization Considerations  . . . . . . . . . . . . . 22
   8.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 23
     8.1.  SASL Registration  . . . . . . . . . . . . . . . . . . . . 23
     8.2.  GSS-API Registration . . . . . . . . . . . . . . . . . . . 24
   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 25
     9.1.  Normative References . . . . . . . . . . . . . . . . . . . 25
     9.2.  Informative References . . . . . . . . . . . . . . . . . . 26
   Appendix A.  Acknowlegements . . . . . . . . . . . . . . . . . . . 28
   Appendix B.  Document History  . . . . . . . . . . . . . . . . . . 29
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 32



















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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
   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] 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, this
   functionality is described in separate specifications, such as the
   bearer token specification [RFC6750].  OAuth 1.0a included 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 and the GSS-API.  Hence, this document takes
   advantage of the OAuth protocol and its deployment base to provide a
   way to use SASL [RFC4422] and the GSS-API [RFC2743] 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
   or the GSS-API 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 -----|               |  |GSS-
   |        |                                  |               |  |API
   +--------+                                  +---------------+  |
                                                              ----+

                     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 mechanisms.  It
   provides a structured interface between protocols and mechanisms.
   The resulting framework allows new protocols to reuse existing
   mechanisms and allows old protocols to make use of new mechanisms.
   The framework also provides a protocol for securing subsequent
   protocol exchanges within a data security layer.

   The Generic Security Service Application Program Interface (GSS-API)
   [RFC2743] provides a framework for applications to support multiple
   authentication mechanisms through a unified interface.

   This document defines SASL mechanisms for OAuth, and it conforms to
   the new bridge between SASL and the GSS-API called GS2 [RFC5801].
   This means that this document defines both SASL and GSS-API
   mechanisms.  Implementers may be interested in either the SASL, the
   GSS-API, or even both mechanisms.  To facilitate these two variants,
   the description has been split into two parts, one part that provides
   normative references for those interested in the SASL OAuth mechanism
   (see Section 3), and a second part for those implementers that wish
   to implement the GSS-API portion (see Section 4).




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   When OAuth is integrated into SASL and the GSS-API 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.

      (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 [RFC6750] 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 [I-D.ietf-appsawg-webfinger].  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.





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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].

   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.





































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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].

      OAUTH10A-PLUS:  Adds channel binding [RFC5056] capability to
         OAUTH10A for protection against man-in-the-middle attacks.
         OAUTH10A-PLUS mandates the usage of Transport Layer Security
         (TLS).

   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.  New channel binding enabled "-PLUS" mechanisms
   defined in this way MUST include message integrity protection.  A
   newly defined mechanism would also need to register a new GS2 OID.

   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.




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   o  Client sends a dummy client response.

   o  Server fails the authentication.

3.1.  Initial Client Response

   Client responses are a key/value pair sequence.  The initial client
   response includes a gs2-header as defined in GS2 [RFC5801], which
   carries the authorization ID.  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
     ;; gs2-header  = As defined in GSS-API
     initial_client_resp = gs2-header kvsep client_resp

   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.  In non-channel binding mechanisms
         this is reserved, the client SHOUD NOT send it, and has the
         default value of "".  In "-PLUS" variants this carries a single
         key value pair "cbdata" for the channel binding data payload
         formatted as an HTTP query string.

   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.



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3.1.1.  Reserved Key/Values

   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 "".

3.1.2.  Use of the gs2-header

   The OAuth scheme related mechanisms are also GSS-API mechanisms, see
   Section 4 for further detail.  The gs2-header is used as follows:

   o  The "gs2-nonstd-flag" MUST NOT be present.

   o  The "gs2-authzid" carries the authorization identity as specified
      in [RFC5801].  If present the application MUST determine whether
      access is granted for the identity asserted in the OAuth
      credential, if it does not the server MUST fail the negotiation.

   In the non "-PLUS" mechanisms the "gs2-cb-flag" MUST be set to "n"
   because channel-binding [RFC5056] data is not expected.  In the
   OAUTH10A-PLUS mechanism (or other -PLUS variants based on this
   specification) the "gs2-cb-flag" MUST be set appropriately by the
   client.

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.

   In a "-PLUS" mechanism the server examines the channel binding data,
   extracts the channel binding unique prefix, and extracts the raw
   channel biding data based on the channel binding type used.  It then
   computes it's own copy of the channel binding payload and compares



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   that to the payload sent by the client in the cbdata key/value.
   Those two must be equal for channel binding to succeed.

   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, such as a GSS-API [RFC2743] named type like
   GSS_C_NT_USER_NAME or a comparable newly defined GSS-API name type or
   name attribute [RFC6680].

3.2.2.  Server Response to Failed Authentication

   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.



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   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
   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",



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              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

3.4.  Channel Binding

   The channel binding data is carried in the "qs" (query string) key
   value pair formatted as a standard HTTP query parameter with the name
   "cbdata".  Channel binding requires that the channel binding data be
   integrity protected end-to-end in order to protect against man-in-
   the-middle attacks.  All SASL OAuth mechanisms with a "-PLUS" postfix
   MUST provide integrity protection.  It should be noted that while the
   OAuth 2.0 Bearer Token mandates TLS it does not create keying
   material at the application layer and is not suitable for use with
   channel bindings.

   The channel binding data is computed by the client based on it's
   choice of preferred channel binding type.  As specified in [RFC5056],
   the channel binding information MUST start with the channel binding
   unique prefix, followed by a colon (ASCII 0x3A), followed by a base64
   encoded channel binding payload.  The channel binding payload is the
   raw data from the channel binding type.  For example, if the client
   is using tls-unique for channel binding then the raw channel binding
   data is the TLS finished message as specified in Section 3.1 of
   [RFC5929].








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4.  GSS-API OAuth Mechanism Specification

   Note: The normative references in this section are informational for
   SASL implementers, but they are normative for GSS-API implementers.

   A SASL OAuth mechanism is also a GSS-API mechanism and the messages
   described in Section 3 are the same with the following changes to the
   GS2 related elements:

   1.  the GS2 header on the client's first message is excluded when
       used as a GSS-API mechanism.

   2.  the initial context token header is prefixed to the client's
       first authentication message (context token), as described in
       Section 3.1 of RFC 2743 [RFC2743],

   The GSS-API mechanism OIDs are:

   o  OAUTHBEARER: [[TBD: IANA -- probably in the 1.3.6.1.5.5 tree]]

   o  OAUTH10A: [[TBD: IANA -- probably in the 1.3.6.1.5.5 tree]]

   o  OAUTH10A-PLUS: [[TBD: IANA -- probably in the 1.3.6.1.5.5 tree]]

   The setting of the security context flags depends on the selected
   mechanism:

   o  OAUTHBEARER: The mutual_state flag (GSS_C_MUTUAL_FLAG) MUST be set
      to FALSE since the TLS protocol execution happens outside the
      SASL/GSS-API method.  Server-side authentication is accomplished
      via the mandatory use of TLS at the application layer utilizing
      SASL.  Without TLS usage at the application layer protecting the
      by OAuth Bearer Token this SASL method is insecure.

   o  OAUTH10A: The mutual_state flag (GSS_C_MUTUAL_FLAG) MUST be set to
      FALSE since server authentication is not provided by this SASL/
      GSS-API method.  Since the TLS channel is managed by the
      application outside of the GSS-API mechanism, the OAUTH10A
      mechanism itself is unable to confirm the name while the
      application is able to perform this comparison for the mechanism.
      For this reason, applications MUST match the TLS server identity
      with the target name using the appropriate application profile, as
      discussed in [RFC6125].  For example, when SASL OAuth is run over
      IMAP then the IMAP profile of RFC 6125 is used.

   o  OAUTH10A-PLUS: The mutual_state flag (GSS_C_MUTUAL_FLAG) MUST be
      set to FALSE since only the client demonstrates possession of the
      session key by applying a keyed message digest function over



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      various fields of the request.  TLS-based server-side
      authentication MUST be provided by the application using SASL.

   Credential delegation is not supported by any of the SASL/GSS-API
   mechanisms with this specification.  Therefore, security contexts
   MUST have the deleg_state flag (GSS_C_DELEG_FLAG) set to FALSE.

   OAuth mechanisms do not support per-message tokens or
   GSS_Pseudo_random.

   OAuth supports a standard generic name syntax for acceptors, such as
   GSS_C_NT_HOSTBASED_SERVICE (see Section 4.1 of [RFC2743]).  These
   service names MUST be associated with the "entityID" claimed by the
   RP.

   OAuth mechanisms support only a single name type for initiators:
   GSS_C_NT_USER_NAME.  GSS_C_NT_USER_NAME is the default name type.

   The query, display, and exported name syntaxes for OAuth principal
   names are all the same.  There is no OAuth-specific name syntax;
   applications SHOULD use generic GSS-API name types, such as
   GSS_C_NT_USER_NAME and GSS_C_NT_HOSTBASED_SERVICE (see Section 4 of
   [RFC2743]).  The exported name token does, of course, conform to
   Section 3.2 of [RFC2743], but the "NAME" part of the token should be
   treated as a potential input string to the OAuth name normalization
   rules.

























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5.  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".

5.1.  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.














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   [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...]

5.2.  OAuth 1.0a Authorization with Channel Binding

   This example shows channel binding in the context of an OAuth 1.0a
   request using a keyed message digest.  Note that line breaks are
   inserted for readability.


  S: * OK [CAPABILITY IMAP4rev1 AUTH=OAUTH10A-PLUS SASL-IR]
        IMAP4rev1 Server Ready
  C: t1 AUTHENTICATE OAUTH10A-PLUS cD10bHMtdW5pcXVlLGE9dXNlckBleGFtcGxlL
        mNvbQFob3N0PXNlcnZlci5leGFtcGxlLmNvbQFwb3J0PTE0MwFhdXRoPU9BdXRoI
        HJlYWxtPSJFeGFtcGxlIixvYXV0aF9jb25zdW1lcl9rZXk9IjlkamRqODJoNDhka
        nM5ZDIiLG9hdXRoX3Rva2VuPSJra2s5ZDdkaDNrMzlzanY3IixvYXV0aF9zaWduY
        XR1cmVfbWV0aG9kPSJITUFDLVNIQTEiLG9hdXRoX3RpbWVzdGFtcD0iMTM3MTMxM
        jAxIixvYXV0aF9ub25jZT0iN2Q4ZjNlNGEiLG9hdXRoX3NpZ25hdHVyZT0iU1Nkd
        ElHRWdiR2wwZEd4bElIUmxZU0J3YjNRdSIBcXM9Y2JkYXRhPXRscy11bmlxdWU6U
        0c5M0lHSnBaeUJwY3lCaElGUk1VeUJtYVc1aGJDQnRaWE56WVdkbFB3bz0BAQ==
  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
   lines wrapped for readability) is:














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   p=tls-unique,a=user@example.com^A
   host=server.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="SSdtIGEgbGl0dGxlIHRlYSBwb3Qu"^A
   qs=cbdata=tls-unique:SG93IGJpZyBpcyBhIFRMUyBmaW5hbCBtZXNzYWdlPwo=^A^A

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


   POST&http%3A%2F%2Fserver.example.com:143%2F&cbdata=tls-unique:SG93I
   GJpZyBpcyBhIFRMUyBmaW5hbCBtZXNzYWdlPwo=%26oauth_consumer_key%3D9djd
   j82h48djs9d2%26oauth_nonce%3D7d8f3e4a%26oauth_signature_method%3DHM
   AC-SHA1%26oauth_timestamp%3D137131201%26oauth_token%3Dkkk9d7dh3k39s
   jv7

5.3.  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.


   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:





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

   The client responds with the required dummy response.

5.4.  Failed Channel Binding

   This example shows a channel binding failure in an empty request.
   The channel binding information is empty.  Note that line breaks are
   inserted for readability.


   S: * CAPABILITY IMAP4rev1 AUTH=OAUTH10A-PLUS SASL-IR IMAP4rev1 Server
        Ready
   S: t0 OK Completed
   C: t1 AUTHENTICATE OAUTH10A-PLUS cCxhPXVzZXJAZXhhbXBsZS5jb20BaG9z
        dD1zZXJ2ZXIuZXhhbXBsZS5jb20BcG9ydD0xNDMBYXV0aD0BY2JkYXRhPQEB
   S: + ewoic3RhdHVzIjoiNDEyIiwKInNjb3BlIjoiZXhhbXBsZV9zY29wZSIKfQ==
   C: + AQ==
   S: t1 NO SASL authentication failed

   The decoded initial client response is:


   p=tls-unique,a=user@example.com,^Ahost=server.example.com^A
   port=143^Aauth=^Acbdata=^A^A

   The decoded server response is:


   {
   "status":"412",
   "scope":"example_scope"
   }

   The client responds with the required dummy response.

5.5.  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.






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[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...]

   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.






























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6.  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 and GSS-API 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.

   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/GSS-API mechanism
      only supports client authentication.  If server-side
      authentication is desireable then it must be provided by the
      application underneath the SASL/GSS-API layer.

   OAUTH10A-PLUS:  This mechanism adds the channel binding [RFC5056]
      capability to OAUTH10A for protection against man-in-the-middle
      attacks.  OAUTH10A-PLUS mandates the usage of Transport Layer
      Security (TLS) at the application layer.

















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7.  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 assertion format
   (in JSON format) is still ongoing, see
   [I-D.ietf-oauth-json-web-token].




































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8.  IANA Considerations

8.1.  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

      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

   The IANA is requested to register the following SASL profile:

      SASL mechanism profile: OAUTH10A-PLUS

      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






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8.2.  GSS-API Registration

   IANA is further requested to assign an OID for these GSS mechanisms
   in the SMI numbers registry, with the prefix of
   iso.org.dod.internet.security.mechanisms (1.3.6.1.5.5) and to
   reference this specification in the registry.













































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9.  References

9.1.  Normative References

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

   [RFC2473]  Conta, A. and S. Deering, "Generic Packet Tunneling in
              IPv6 Specification", RFC 2473, December 1998.

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

   [RFC2617]  Franks, J., Hallam-Baker, P., Hostetler, J., Lawrence, S.,
              Leach, P., Luotonen, A., and L. Stewart, "HTTP
              Authentication: Basic and Digest Access Authentication",
              RFC 2617, June 1999.

   [RFC2743]  Linn, J., "Generic Security Service Application Program
              Interface Version 2, Update 1", RFC 2743, January 2000.

   [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.

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

   [RFC5801]  Josefsson, S. and N. Williams, "Using Generic Security
              Service Application Program Interface (GSS-API) Mechanisms



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              in Simple Authentication and Security Layer (SASL): The
              GS2 Mechanism Family", RFC 5801, July 2010.

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

   [RFC5929]  Altman, J., Williams, N., and L. Zhu, "Channel Bindings
              for TLS", RFC 5929, July 2010.

   [RFC5988]  Nottingham, M., "Web Linking", RFC 5988, October 2010.

   [RFC6125]  Saint-Andre, P. and J. Hodges, "Representation and
              Verification of Domain-Based Application Service Identity
              within Internet Public Key Infrastructure Using X.509
              (PKIX) Certificates in the Context of Transport Layer
              Security (TLS)", RFC 6125, March 2011.

   [RFC6680]  Williams, N., Johansson, L., Hartman, S., and S.
              Josefsson, "Generic Security Service Application
              Programming Interface (GSS-API) Naming Extensions",
              RFC 6680, August 2012.

   [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.

9.2.  Informative References

   [I-D.ietf-appsawg-webfinger]
              Jones, P., Salgueiro, G., and J. Smarr, "WebFinger",
              draft-ietf-appsawg-webfinger-10 (work in progress),
              February 2013.

   [I-D.ietf-oauth-json-web-token]
              Jones, M., Bradley, J., and N. Sakimura, "JSON Web Token
              (JWT)", draft-ietf-oauth-json-web-token-06 (work in
              progress), December 2012.

   [I-D.ietf-oauth-v2-http-mac]
              Richer, J., Mills, W., and H. Tschofenig, "OAuth 2.0
              Message Authentication Code (MAC) Tokens",
              draft-ietf-oauth-v2-http-mac-02 (work in progress),
              November 2012.

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



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
















































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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.









































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Appendix B.  Document History

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

   -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.

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





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   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.

   -00






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

   o  Minor fixes.















































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Authors' Addresses

   William Mills
   Yahoo! Inc.


   Phone:
   Email: wmills@yahoo-inc.com


   Tim Showalter


   Phone:
   Email: tjs@psaux.com


   Hannes Tschofenig
   Nokia Siemens 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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