OAuth Working Group                                  T. Lodderstedt, Ed.
Internet-Draft                                       Deutsche Telekom AG
Intended status: Standards Track                               S. Dronia
Expires: August 16, 2013
                                                           M. Scurtescu
                                                       February 12, 2013

                            Token Revocation


   This document proposes an additional endpoint for OAuth authorization
   servers, which allows clients to notify the authorization server that
   a previously obtained refresh or access token is no longer needed.
   This allows the authorization server to cleanup security credentials.
   A revocation request will invalidate the actual token and, if
   applicable, other tokens based on the same authorization grant.

Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC 2119 [RFC2119].

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."

   This Internet-Draft will expire on August 16, 2013.

Copyright Notice

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

Lodderstedt, et al.      Expires August 16, 2013                [Page 1]

Internet-Draft              Token Revocation               February 2013

   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  . . . . . . . . . . . . . . . . . . . . . . . . . 3
   2.  Token Revocation  . . . . . . . . . . . . . . . . . . . . . . . 3
     2.1.  Revocation Request  . . . . . . . . . . . . . . . . . . . . 4
     2.2.  Revocation Response . . . . . . . . . . . . . . . . . . . . 5
       2.2.1.  Error Response  . . . . . . . . . . . . . . . . . . . . 5
     2.3.  Cross-Origin Support  . . . . . . . . . . . . . . . . . . . 5
   3.  Implementation Note . . . . . . . . . . . . . . . . . . . . . . 6
   4.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . 7
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 7
   6.  Security Considerations . . . . . . . . . . . . . . . . . . . . 7
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 8
     7.1.  Normative References  . . . . . . . . . . . . . . . . . . . 8
     7.2.  Informative References  . . . . . . . . . . . . . . . . . . 8
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . . 9

Lodderstedt, et al.      Expires August 16, 2013                [Page 2]

Internet-Draft              Token Revocation               February 2013

1.  Introduction

   The OAuth 2.0 core specification [RFC6749] defines several ways for a
   client to obtain refresh and access tokens.  This specification
   supplements the core specification with a mechanism to revoke both
   types of tokens.  A token is a string representing an authorization
   grant issued by the resource owner to the client.  A revocation
   request will invalidate the actual token and, if applicable, other
   tokens based on the same authorization grant and the authorization
   grant itself.

   From an end-user's perspective, OAuth is often used to log into a
   certain site or app.  This revocation mechanism allows a client to
   invalidate its tokens if the end-user logs out, changes identity, or
   uninstalls the respective app.  Notifying the authorization server
   that the token is no longer needed allows the authorization server to
   clean up data associated with that token (e.g. session data) and the
   underlying authorization grant.  This behavior prevents a situation
   where there is still a valid authorization grant for a particular
   client which the end user is not aware of.  This way, token
   revocation prevents abuse of abandoned tokens and facilitates a
   better end-user experience since invalidated authorization grants
   will no longer turn up in a list of authorization grants the
   authorization server might present to the end-user.

2.  Token Revocation

   Implementations MUST support the revocation of refresh tokens and
   SHOULD support the revocation of access tokens (see Implementation

   The client requests the revocation of a particular token by making an
   HTTP POST request to the token revocation endpoint URL.  The token
   endpoint URL MAY include a query component.  The means to obtain the
   location of the revocation endpoint is out of scope of this
   specification.  For example, the client developler may consult the
   server's documentation or automatic discovery may be used.  As this
   endpoint is handling security credentials, the endpoint location MUST
   be obtained from a trustworthy source.

   Since requests to the token revocation endpoint result in the
   transmission of plain text credentials in the HTTP request, the
   authorization server MUST require the use of a transport-layer
   security mechanism when sending requests to the token revocation
   endpoints.  The authorization server MUST support TLS 1.0
   ([RFC2246]), SHOULD support TLS 1.2 ([RFC5246]) and its future
   replacements, and MAY support additional transport-layer mechanisms

Lodderstedt, et al.      Expires August 16, 2013                [Page 3]

Internet-Draft              Token Revocation               February 2013

   meeting its security requirements.

2.1.  Revocation Request

   The client constructs the request by including the following
   parameters using the "application/x-www-form-urlencoded" format in
   the HTTP request entity-body:

   token   REQUIRED.  The token that the client wants to get revoked.

   token_type_hint  OPTIONAL.  A hint about the type of the token
           submitted for revocation.  Clients MAY pass this parameter in
           order to help the authorization server to optimize the token
           lookup.  If the server is unable to locate the token using
           the given hint, it MUST extend its search accross all of its
           supported token types.  An authorization server MAY ignore
           this parameter, particularly if it is able to detect the
           token type automatically.  This specification defines two
           such values:

           *       access_token An Access Token as defined in [RFC6749]
                   section 1.4

           *       refresh_token A Refresh Token as defined in [RFC6749]
                   section 1.5

           Specific implementations, profiles, and extensions of this
           specification MAY define other values for this parameter.

   The client also includes its authentication credentials as described
   in Section 2.3. of [RFC6749].

   For example, a client may request the revocation of a refresh token
   with the following request (line breaks are for display purposes

     POST /revoke HTTP/1.1
     Host: server.example.com
     Content-Type: application/x-www-form-urlencoded
     Authorization: Basic czZCaGRSa3F0MzpnWDFmQmF0M2JW


   The authorization server first validates the client credentials (in
   case of a confidential client) and then verifies whether the token
   was issued to the client making the revocation request.  If this

Lodderstedt, et al.      Expires August 16, 2013                [Page 4]

Internet-Draft              Token Revocation               February 2013

   validation fails, the request is refused and the client is informed
   of the error by the authorization server as described below.

   In the next step, the authorization server invalidates the token.
   The client MUST assume the revocation is immediate upon the return of
   the request.  The client MUST NOT use the token again after the

   Depending on the authorization server's revocation policy, the
   revocation of a particular token may cause the revocation of related
   tokens and the underlying authorization grant.  If the particular
   token is a refresh token and the authorization server supports the
   revocation of access tokens, then the authorization server SHOULD
   also invalidate all access tokens based on the same authorization
   grant (see Implementation Note).  If the token passed to the request
   is an access token, the server MAY decide to revoke the respective
   refresh token as well.

   Note: A client compliant with [RFC6749] must be prepared to handle
   unexpected token invalidation at any time.  Independent of the
   revocation mechanism specified in this document, resource owners may
   decide to revoke authorization grants or the authorization server may
   invalidate tokens in order to mitigate security threats.  Thus having
   different server policies with respect to cascading the revocation of
   tokens should not pose interoperability problems.

2.2.  Revocation Response

   The authorization server indicates a successful processing of the
   request by a HTTP status code 200.  This also applies if the client
   submits an invalid token to the revocation endpoint.

2.2.1.  Error Response

   The error presentation conforms to the defintion in section 5.2 of
   [RFC6749].  The following additional error code is defined for the
   token revocation endpoint:

   unsupported_token_type  The authorization server does not support the
           revocation of the presented token type.  I.e. the client
           tried to revoke an access token on a server not supporting
           this feature.

2.3.  Cross-Origin Support

   The revocation end-point MAY support CORS [W3C.WD-cors-20120403] if
   it is aimed at use in combination with user-agent-based applications.

Lodderstedt, et al.      Expires August 16, 2013                [Page 5]

Internet-Draft              Token Revocation               February 2013

   In addition, for interoperability with legacy user-agents, it MAY
   also offer JSONP [jsonp] by allowing GET requests with an additional

   callback  OPTIONAL.  The qualified name of a JavaScript function.

   For example, a client may request the revocation of an access token
   with the following request (line breaks are for display purposes


   Successful response:


   Error response:


   Clients should be aware that when relying on JSONP, a malicious
   revocation end-point may attempt to inject malicious code into the

3.  Implementation Note

   OAuth 2.0 allows deployment flexibility with respect to the style of
   access tokens.  The access tokens may be self-contained so that an
   resource server needs no further interaction with an authorization
   server issuing these tokens to perform an authorization decision of
   the client requesting access to a protected resource.  A system
   design may, however, instead use access tokens that are handles
   referring to authorization data stored at the authorization server.
   This consequently requires a resource server to issue a request to
   the respective authorization server to retrieve the content of the
   access token every time a client presents an access token.

   While these are not the only options they illustrate the implications
   for revocation.  In the latter case the authorization server is able
   to revoke an access token previously issued to a client when the
   resource server relays a received access token.  In the former case
   some (currently non-standardized) backend interaction between the
   authorization server and the resource server may be used when
   immediate access token revocation is desired.  Another design
   alternative is to issue short-lived access tokens, which can be
   refreshed at any time using the corresponding refresh tokens.  This

Lodderstedt, et al.      Expires August 16, 2013                [Page 6]

Internet-Draft              Token Revocation               February 2013

   allows the authorization server to impose a limit on the time revoked
   access tokens are in use.

   Which approach of token revocation is chosen will depend on the
   overall system design and on the application service provider's risk
   analysis.  The cost of revocation in terms of required state and
   communication overhead is ultimately the result of the desired
   security properties.

4.  Acknowledgements

   We would like to thank Peter, Mauritius, Amanda Anganes, Mark Wubben,
   Hannes Tschofenig, Michiel de Jong, Doug Foiles, Paul Madsen, George
   Fletcher, Sebastian Ebling, Christian Stuebner, Brian Campbell, Igor
   Faynberg, Lukas Rosenstock, and Justin Richer for their valuable

5.  IANA Considerations

   This draft includes no request to IANA.

6.  Security Considerations

   If the authorization server does not support access token revocation,
   access tokens will not be immediately invalidated when the
   corresponding refresh token is revoked.  Deployments MUST take this
   into account when conducting their security risk analysis.

   Cleaning up tokens using revocation contributes to overall security
   and privacy since it reduces the likelihood for abuse of abandoned
   tokens.  This specification in general does not intend to provide
   countermeasures against token theft and abuse.  For a discussion of
   respective threats and countermeasures, consult the security
   considerations given in section 10 of the OAuth core specification
   [RFC6749] and the OAuth threat model document

   Malicious clients could attempt to use the new endpoint to launch
   denial of service attacks on the authorization server.  Appropriate
   countermeasures, which should be in place for the token endpoint as
   well, MUST be applied to the revocation endpoint (see
   [I-D.ietf-oauth-v2-threatmodel], section

   A malicious client may attempt to guess valid tokens on this endpoint
   by making revocation requests against potential token strings.

Lodderstedt, et al.      Expires August 16, 2013                [Page 7]

Internet-Draft              Token Revocation               February 2013

   According to this specification, a client's request must contain a
   valid client_id, in the case of a public client, or valid client
   credentials, in the case of a confidential client.  The token being
   revoked must also belong to the requesting client.  If an attacker is
   able to successfully guess a public client's client_id and one of
   their tokens, or a private client's credentials and one of their
   tokens, they could do much worse damage by using the token elsewhere
   than by revoking it.  If they chose to revoke the token, the
   legitimate client will lose its authorization grant and will need to
   prompt the user again.  No further damage is done and the guessed
   token is now worthless.

   Since the revocation endpoint is handling security credentials,
   clients shall obtain its location from a trustworthy source only.
   Otherwise, an attacker could capture valid security tokens by
   utilizing a counterfeit revocation endpoint.

7.  References

7.1.  Normative References

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

   [RFC2246]  Dierks, T. and C. Allen, "The TLS Protocol Version 1.0",
              RFC 2246, January 1999.

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

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

7.2.  Informative References

              Lodderstedt, T., McGloin, M., and P. Hunt, "OAuth 2.0
              Threat Model and Security Considerations",
              draft-ietf-oauth-v2-threatmodel-08 (work in progress),
              October 2012.

              Kesteren, A., "Cross-Origin Resource Sharing", World Wide
              Web Consortium LastCall WD-cors-20120403, April 2012,

   [jsonp]    Ippolito, B., "Remote JSON - JSONP", December 2005.

Lodderstedt, et al.      Expires August 16, 2013                [Page 8]

Internet-Draft              Token Revocation               February 2013

Authors' Addresses

   Torsten Lodderstedt (editor)
   Deutsche Telekom AG

   Email: torsten@lodderstedt.net

   Stefanie Dronia

   Email: sdronia@gmx.de

   Marius Scurtescu

   Email: mscurtescu@google.com

Lodderstedt, et al.      Expires August 16, 2013                [Page 9]