OAuth Working Group                                  T. Lodderstedt, Ed.
Internet-Draft                                       Deutsche Telekom AG
Intended status: Standards Track                               S. Dronia
Expires: May 28, 2013
                                                           M. Scurtescu
                                                       November 24, 2012

                            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 access 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
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   This Internet-Draft will expire on May 28, 2013.

Copyright Notice

   Copyright (c) 2012 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   This document is subject to BCP 78 and the IETF Trust's Legal
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   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
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   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.  Cross-Origin Support  . . . . . . . . . . . . . . . . . . . 5
   3.  Implementation Note . . . . . . . . . . . . . . . . . . . . . . 5
   4.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . 6
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6
   6.  Security Considerations . . . . . . . . . . . . . . . . . . . . 6
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 7
     7.1.  Normative References  . . . . . . . . . . . . . . . . . . . 7
     7.2.  Informative References  . . . . . . . . . . . . . . . . . . 7
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . . 7

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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 the external representation of an access
   grant issued by a resource owner to a particular client.  A
   revocation request will invalidate the actual token and, if
   applicable, other tokens based on the same access grant and the
   access grant itself.

   From an end-user's perception, 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 access grant.  This behavior prevents a situation where
   there is still a valid access 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 access grants will no longer turn up in a list of
   access grants the authorization server might present to the end-user.

2.  Token Revocation

   The client requests the revocation of a particular token by making an
   HTTP POST request to the token revocation endpoint.  The location of
   the token revocation endpoint can be found in the authorization
   server's documentation.  The token endpoint URI MAY include a query

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

   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
   meeting its security requirements.

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

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   the HTTP request entity-body:

   token   REQUIRED.  The token that the client wants to get revoked.
           Note: the authorization server is supposed to detect the
           token type automatically.

   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 verifies whether the client is
   authorized to revoke the particular token.  These checks are used to
   validate whether the token being presented has been issued to the
   client presenting it.

   In the next step, the authorization server invalidates the token and
   the respective access 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 access grant (see Implementation

   The client MUST NOT use the token again after revocation.

   The authorization server indicates a successful processing of the
   request by a HTTP status code 200.  Status code 401 indicates a
   failed client authentication, whereas a status code 403 is used if
   the client is not authorized to revoke the particular token.  For all
   other error conditions, a status code 400 is used along with an error
   response as defined in section 5.2. of [RFC6749].  The following
   error codes are 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.

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   invalid_token  The presented token is invalid.

2.1.  Cross-Origin Support

   The revokation end-point SHOULD support CORS [W3C.WD-cors-20120403]
   if it is aimed at use in combination with user-agent-based
   applications.  In addition, for interoperability with legacy user-
   agents, it MAY offer JSONP [jsonp] by allowing GET requests with an
   additional parameter:

   callback  The qualified name of a JavaScript function.

   Example request:


   Successful response:


   Error response:


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

3.  Implementation Note

   Depending on the authorization server's token design, revocation of
   access tokens might be a costly process.  For example, revocation of
   self-contained access tokens requires (time-consuming) backend calls
   between resource and authorization server on every request to the
   resource server or to push notifications from the authorization
   server to the affected resource servers.  Alternatively,
   authorization servers may choose to issue short living access tokens,
   which can be refreshed at any time using the corresponding refresh
   tokens.  In this case, a client would revoke the refresh token and
   access tokens issued based on this particular refresh token are at
   most valid until expiration.  Whether this is an viable option or
   whether access token revocation is required should be decided based
   on the service provider's risk analysis.

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4.  Acknowledgements

   We would like to thank 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 feedback.

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
   in 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.

   A malicious client may attempt to guess valid tokens on this
   endpoints.  As a pre-requisite, the client either requires a valid
   client_id of a public client or the credentials of a confidential
   client.  An sucessful attempt would result in the revocation of the
   respective token, thus causing the legitimate client to lose its
   authorization.  The malicious client does not gain further

7.  References

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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.

Authors' Addresses

   Torsten Lodderstedt (editor)
   Deutsche Telekom AG

   Email: torsten@lodderstedt.net

   Stefanie Dronia

   Email: sdronia@gmx.de

   Marius Scurtescu

   Email: mscurtescu@google.com

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