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rfc:rfc7009

Internet Engineering Task Force (IETF) T. Lodderstedt, Ed. Request for Comments: 7009 Deutsche Telekom AG Category: Standards Track S. Dronia ISSN: 2070-1721

                                                          M. Scurtescu
                                                                Google
                                                           August 2013
                     OAuth 2.0 Token Revocation

Abstract

 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 clean up security
 credentials.  A revocation request will invalidate the actual token
 and, if applicable, other tokens based on the same authorization
 grant.

Status of This Memo

 This is an Internet Standards Track document.
 This document is a product of the Internet Engineering Task Force
 (IETF).  It represents the consensus of the IETF community.  It has
 received public review and has been approved for publication by the
 Internet Engineering Steering Group (IESG).  Further information on
 Internet Standards is available in Section 2 of RFC 5741.
 Information about the current status of this document, any errata,
 and how to provide feedback on it may be obtained at
 http://www.rfc-editor.org/info/rfc7009.

Lodderstedt, et al. Standards Track [Page 1] RFC 7009 Token Revocation August 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.

Table of Contents

 1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
 2.  Token Revocation  . . . . . . . . . . . . . . . . . . . . . .   3
   2.1.  Revocation Request  . . . . . . . . . . . . . . . . . . .   4
   2.2.  Revocation Response . . . . . . . . . . . . . . . . . . .   5
     2.2.1.  Error Response  . . . . . . . . . . . . . . . . . . .   6
   2.3.  Cross-Origin Support  . . . . . . . . . . . . . . . . . .   6
 3.  Implementation Note . . . . . . . . . . . . . . . . . . . . .   7
 4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   8
   4.1.  OAuth Extensions Error Registration . . . . . . . . . . .   8
     4.1.1.  The "unsupported_token_type" Error Value  . . . . . .   8
     4.1.2.  OAuth Token Type Hints Registry . . . . . . . . . . .   8
       4.1.2.1.  Registration Template . . . . . . . . . . . . . .   9
       4.1.2.2.  Initial Registry Contents . . . . . . . . . . . .   9
 5.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
 6.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  10
 7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  10
   7.1.  Normative References  . . . . . . . . . . . . . . . . . .  10
   7.2.  Informative References  . . . . . . . . . . . . . . . . .  11

Lodderstedt, et al. Standards Track [Page 2] RFC 7009 Token Revocation August 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 application.  This revocation mechanism allows a
 client to invalidate its tokens if the end-user logs out, changes
 identity, or uninstalls the respective application.  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 in which there is still a valid
 authorization grant for a particular client of which the end-user is
 not aware.  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.

1.1. Requirements Language

 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 RFC 2119 [RFC2119].

2. Token Revocation

 Implementations MUST support the revocation of refresh tokens and
 SHOULD support the revocation of access tokens (see Implementation
 Note).
 The client requests the revocation of a particular token by making an
 HTTP POST request to the token revocation endpoint URL.  This URL
 MUST conform to the rules given in [RFC6749], Section 3.1.  Clients
 MUST verify that the URL is an HTTPS URL.
 The means to obtain the location of the revocation endpoint is out of
 the scope of this specification.  For example, the client developer
 may consult the server's documentation or automatic discovery may be
 used.  As this endpoint is handling security credentials, the
 endpoint location needs to be obtained from a trustworthy source.

Lodderstedt, et al. Standards Track [Page 3] RFC 7009 Token Revocation August 2013

 Since requests to the token revocation endpoint result in the
 transmission of plaintext credentials in the HTTP request, URLs for
 token revocation endpoints MUST be HTTPS URLs.  The authorization
 server MUST use Transport Layer Security (TLS) [RFC5246] in a version
 compliant with [RFC6749], Section 1.6.  Implementations MAY also
 support additional transport-layer security mechanisms that meet
 their security requirements.
 If the host of the token revocation endpoint can also be reached over
 HTTP, then the server SHOULD also offer a revocation service at the
 corresponding HTTP URI, but it MUST NOT publish this URI as a token
 revocation endpoint.  This ensures that tokens accidentally sent over
 HTTP will be revoked.

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 across 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
         using the registry defined in Section 4.1.2.
 The client also includes its authentication credentials as described
 in Section 2.3. of [RFC6749].

Lodderstedt, et al. Standards Track [Page 4] RFC 7009 Token Revocation August 2013

 For example, a client may request the revocation of a refresh token
 with the following request:
   POST /revoke HTTP/1.1
   Host: server.example.com
   Content-Type: application/x-www-form-urlencoded
   Authorization: Basic czZCaGRSa3F0MzpnWDFmQmF0M2JW
   token=45ghiukldjahdnhzdauz&token_type_hint=refresh_token
 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
 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 invalidation takes place immediately, and the token cannot be
 used again after the revocation.  In practice, there could be a
 propagation delay, for example, in which some servers know about the
 invalidation while others do not.  Implementations should minimize
 that window, and clients must not try to use the token after receipt
 of an HTTP 200 response from the server.
 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 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
 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 responds with HTTP status code 200 if the
 token has been revoked successfully or if the client submitted an
 invalid token.

Lodderstedt, et al. Standards Track [Page 5] RFC 7009 Token Revocation August 2013

 Note: invalid tokens do not cause an error response since the client
 cannot handle such an error in a reasonable way.  Moreover, the
 purpose of the revocation request, invalidating the particular token,
 is already achieved.
 The content of the response body is ignored by the client as all
 necessary information is conveyed in the response code.
 An invalid token type hint value is ignored by the authorization
 server and does not influence the revocation response.

2.2.1. Error Response

 The error presentation conforms to the definition 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.  That is, the
         client tried to revoke an access token on a server not
         supporting this feature.
 If the server responds with HTTP status code 503, the client must
 assume the token still exists and may retry after a reasonable delay.
 The server may include a "Retry-After" header in the response to
 indicate how long the service is expected to be unavailable to the
 requesting client.

2.3. Cross-Origin Support

 The revocation endpoint MAY support Cross-Origin Resource Sharing
 (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
 also offer JSONP (Remote JSON - JSONP) [jsonp] by allowing GET
 requests with an additional parameter:
 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
 only):
   https://example.com/revoke?token=agabcdefddddafdd&
   callback=package.myCallback

Lodderstedt, et al. Standards Track [Page 6] RFC 7009 Token Revocation August 2013

 Successful response:
   package.myCallback();
 Error response:
   package.myCallback({"error":"unsupported_token_type"});
 Clients should be aware that when relying on JSONP, a malicious
 revocation endpoint may attempt to inject malicious code into the
 client.

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 a
 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 allows the authorization server to impose a limit on
 the time revoked when 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.

Lodderstedt, et al. Standards Track [Page 7] RFC 7009 Token Revocation August 2013

4. IANA Considerations

 This specification registers an error value in the "OAuth Extensions
 Error Registry" and establishes the "OAuth Token Type Hints"
 registry.

4.1. OAuth Extensions Error Registration

 This specification registers the following error value in the "OAuth
 Extensions Error Registry" defined in [RFC6749].

4.1.1. The "unsupported_token_type" Error Value

 Error name:  unsupported_token_type
 Error Usage Location:  Revocation endpoint error response
 Related Protocol Extension:  Token Revocation Endpoint
 Change controller:  IETF
 Specification document(s):  [RFC7009]

4.1.2. OAuth Token Type Hints Registry

 This specification establishes the "OAuth Token Type Hints" registry.
 Possible values of the parameter "token_type_hint" (see Section 2.1)
 are registered with a Specification Required ([RFC5226]) after a two-
 week review period on the oauth-ext-review@ietf.org mailing list, on
 the advice of one or more Designated Experts.  However, to allow for
 the allocation of values prior to publication, the Designated
 Expert(s) may approve registration once they are satisfied that such
 a specification will be published.  Registration requests must be
 sent to the oauth-ext-review@ietf.org mailing list for review and
 comment, with an appropriate subject (e.g., "Request for parameter:
 example").  Within the review period, the Designated Expert(s) will
 either approve or deny the registration request, communicating this
 decision to the review list and IANA.  Denials should include an
 explanation and, if applicable, suggestions as to how to make the
 request successful.  IANA must only accept registry updates from the
 Designated Expert(s) and should direct all requests for registration
 to the review mailing list.

Lodderstedt, et al. Standards Track [Page 8] RFC 7009 Token Revocation August 2013

4.1.2.1. Registration Template

 Hint Value:  The additional value, which can be used to indicate a
    certain token type to the authorization server.
 Change controller:  For Standards Track RFCs, state "IETF".  For
    others, give the name of the responsible party.  Other details
    (e.g., postal address, email address, and home page URI) may also
    be included.
 Specification document(s):  Reference to the document(s) that
    specifies the type, preferably including a URI that can be used to
    retrieve a copy of the document(s).  An indication of the relevant
    sections may also be included but is not required.

4.1.2.2. Initial Registry Contents

 The OAuth Token Type Hint registry's initial contents are as follows.
           +---------------+-------------------+-----------+
           |   Hint Value  | Change Controller | Reference |
           +---------------+-------------------+-----------+
           |  access_token |        IETF       | [RFC7009] |
           | refresh_token |        IETF       | [RFC7009] |
           +---------------+-------------------+-----------+
       Table 1: OAuth Token Type Hints initial registry contents

5. 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 [RFC6819].
 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 [RFC6819],
 Section 4.4.1.11).  Specifically, invalid token type hints may

Lodderstedt, et al. Standards Track [Page 9] RFC 7009 Token Revocation August 2013

 misguide the authorization server and cause additional database
 lookups.  Care MUST be taken to prevent malicious clients from
 exploiting this feature to launch denial-of-service attacks.
 A malicious client may attempt to guess valid tokens on this endpoint
 by making revocation requests against potential token strings.
 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 need to obtain its location from a trustworthy source only.
 Otherwise, an attacker could capture valid security tokens by
 utilizing a counterfeit revocation endpoint.  Moreover, in order to
 detect counterfeit revocation endpoints, clients MUST authenticate
 the revocation endpoint (certificate validation, etc.).

6. 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
 feedback.

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.
 [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
            IANA Considerations Section in RFCs", BCP 26, RFC 5226,
            May 2008.
 [RFC5246]  Dierks, T. and E. Rescorla, "The Transport Layer Security
            (TLS) Protocol Version 1.2", RFC 5246, August 2008.

Lodderstedt, et al. Standards Track [Page 10] RFC 7009 Token Revocation August 2013

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

7.2. Informative References

 [RFC6819]  Lodderstedt, T., McGloin, M., and P. Hunt, "OAuth 2.0
            Threat Model and Security Considerations", RFC 6819,
            January 2013.
 [W3C.WD-cors-20120403]
            Kesteren, A., "Cross-Origin Resource Sharing", World Wide
            Web Consortium LastCall WD-cors-20120403, April 2012,
            <http://www.w3.org/TR/2012/WD-cors-20120403>.
 [jsonp]    Ippolito, B., "Remote JSON - JSONP", December 2005,
            <http://bob.pythonmac.org/archives/2005/12/05/
            remote-json-jsonp>.

Authors' Addresses

 Torsten Lodderstedt (editor)
 Deutsche Telekom AG
 EMail: torsten@lodderstedt.net
 Stefanie Dronia
 EMail: sdronia@gmx.de
 Marius Scurtescu
 Google
 EMail: mscurtescu@google.com

Lodderstedt, et al. Standards Track [Page 11]

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