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Network Working Group                                          J. Richer
Internet-Draft                                     The MITRE Corporation
Intended status: Standards Track                      September 07, 2012
Expires: March 11, 2013


     A Method of Bearer Token Redelegation and Chaining for OAuth 2
                        draft-richer-oauth-chain-00

Abstract

   This document provides a method for a resource server to present a
   token that it has received from a client back to its authorization
   server for the purposes of receiving a derivative token for use on
   another resource server in order to chain together service requests.

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].

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 March 11, 2013.

Copyright Notice

   Copyright (c) 2012 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



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   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.  Service Chaining  . . . . . . . . . . . . . . . . . . . . . . . 3
     1.1.  Abbreviations Used In This Document . . . . . . . . . . . . 3
   2.  Protocol Description  . . . . . . . . . . . . . . . . . . . . . 4
   3.  Redelegation Grant Type . . . . . . . . . . . . . . . . . . . . 5
     3.1.  Redelegate Request  . . . . . . . . . . . . . . . . . . . . 6
     3.2.  Access Token Response . . . . . . . . . . . . . . . . . . . 6
     3.3.  Error Response  . . . . . . . . . . . . . . . . . . . . . . 6
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 7
   5.  Security Considerations . . . . . . . . . . . . . . . . . . . . 7
   6.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . 7
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 7
     7.1.  Normative References  . . . . . . . . . . . . . . . . . . . 7
     7.2.  Informative References  . . . . . . . . . . . . . . . . . . 7
   Appendix A.  Standardization of Scopes  . . . . . . . . . . . . . . 7
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . . . 8



























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1.  Service Chaining

   The OAuth2 Authorization protocol provides methods for clients to
   request tokens from authorization servers on behalf of resource
   owners for use at resource servers.  However, there are no provisions
   for a resource server to act as a client itself for another resource
   server, a practice known generally as service chaining.  Typically,
   the services involved in the chain are within a single security
   domain, and with OAuth they would be using a single Authorization
   Server.

   For services using the OAuth2 Bearer token profile, it is possible
   for anyone holding the token to call any other service that accepts
   the token.  While this is functional, it is bad practice since the
   token is knowingly being re-used by someone other than the client to
   which it was issued.  Since the same token is used in each step, this
   approach also does not allow for attenuation of rights as the chain
   progresses.

   Using a new form of grant_type, this specification presents such
   chained resource servers with an alternative approach that takes
   advantage of the simplicity and structure of the OAuth protocol by
   providing a means for any resource server to present the token it has
   been accessed with back to the authorization server in order to
   exchange it for a token of equal or lesser strength for use with
   another resource server.  In this way, the original access token
   which has been delegated to the client can be redelegated to a
   secondary service.

   This approach differs slightly from the Refresh Token described in
   the OAuth 2 Core.  With a Refresh Token, the Client presents the
   token to the authorization server to get a new Access Token without
   involving the Resource Owner.  With a redelegated Access Token, as
   described in this document, the Resource Server presents the Access
   Token which was provided to it by a Client in order to get a
   secondary Access Token.

1.1.  Abbreviations Used In This Document

   AS Authorization Server

   C  Client

   RO Resource Owner







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   RS1  Primary Resource Server, initially called by C on behalf of RO

   RS2  Chained Resource Server, called by RS1 to fulfill request from C

   AT1  Bearer Access Token granted by AS to C to access RS1 on behalf
      of RO

   AT2  Bearer Access Token granted by AS to RS1 to access RS2 on behalf
      of RO


2.  Protocol Description

   The process begins with any standard OAuth2 protocol flow, where the
   client obtains AT1 from the AS.

   The beginning of the process is standard OAuth2 S.1.2 using any legal
   OAuth2 grant type to obtain the AT1.

     +--------+       +-------------+
     |        |--(A)->|  Resource   |
     |        |       |   Owner     |
     |        |<-(B)--|   (RO)      |
     |        |       +-------------+
     |        |
     |        |                             +---------------+
     |        |--(C)----------------------->| Authorization |
     | Client |                             |     Server    |
     |        |<-(D)------------------------|      (AS)     |
     |        |                             |               |
     |        |                             |               |
     |        |       +-------------+       |               |
     |        |--(E)->|  Primary    |--(F)->|               |
     |        |       |  Resource   |       |               |
     |        |       |   Server    |<-(G)--|               |
     |        |       |   (RS1)     |       +---------------+
     |        |       |             |
     |        |       |             |       +---------------+
     |        |       |             |--(H)->|   Chained     |
     |        |       |             |       |   Resource    |
     |        |       |             |       |    Server     |
     |        |       |             |<-(I)--|    (RS2)      |
     |        |<-(J)--|             |       +---------------+
     +--------+       +-------------+







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   (A)  Client requests authorization from Resource Owner

   (B)  Client receives authorization from the Resource Owner using any
      valid OAuth2 grant type

   (C)  Client requests AT1 from the AS by authenticating with the AS
      and presenting the authorization grant obtained in (B)

   (D)  AS authenticates the Client and issues access token AT1 for use
      at RS1

   (E)  Client presents access token AT1 to RS1 to access a protected
      resource

   (F)  RS1 needs to access RS2 to fulfill this request, makes a call to
      the Token Endpoint on the AS using the redelegate grant_type

   (G)  AS validates AT1 and issues a token AT2 for use by RS1 against
      RS2, where the rights assigned to AT2 are a subset of those
      assigned to AT1

   (H)  RS1 presents AT2 to RS2 to access a protected resource

   (I)  RS2 validates token AT2 and returns the protected resource to
      RS1

   (J)  Client receives protected resource from RS1, including
      information sourced from RS2

   Steps A-E and J are standard OAuth2 and OAuth2 Bearer tokens
   involving token AT1.  As such, the Client MAY make use of any OAuth2
   grant type, such as authorization_code, implicit, client_credentials,
   password, assertion, or even the redelegation protocol defined in
   this document.  Steps F-G are described in section 3 of this
   document.  Steps H-I are standard OAuth2 Bearer token usage, but
   using the delegated token AT2.

   The means by which the Resource Servers validate the Access Tokens is
   out of scope of this specification.  At the time of this writing,
   there are two main approaches found in practice: token introspection
   and structured tokens.


3.  Redelegation Grant Type

   The Resource Server RS1 makes a request using the Access Token that
   was presented to it in order to obtain a new Access Token.




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3.1.  Redelegate Request

   To access RS2, RS1 makes a POST request to the Authorization Server's
   Token Endpoint with the following parameters:

   grant_type  REQUIRED.  Value MUST be set to
      "urn:ietf:params:oauth:grant_type:redelegate".

   token  REQUIRED The token that was presented to the resource server
      by the client, referred to as AT1 in the protocol flow, an OAuth2
      Bearer token

   scope  OPTIONAL a space-separated list of strings as described in
      OAuth 2.  If present, this scope list MUST be equal to or lesser
      than the scopes incorporated in AT1.  The AS MUST issue a token of
      equal or lesser scope than the token above.

   The Authorization Server MAY require RS1 to have registered as a
   client on its own behalf.  In this case, RS1 MUST present its client
   credentials as described in OAuth2 Core.

3.2.  Access Token Response

   If the request is valid and authorized, the AS issues an access
   token, referred to as AT2 in the protocol flow, as described in
   OAuth2 Core.  As this access token is bound to an existing access
   token, the authorization server MUST NOT issue a refresh token.  If
   the request failed, the authorization server returns an error
   response as described in OAuth2 Core.

        HTTP/1.1 200 OK
        Content-Type: application/json;charset=UTF-8
        Cache-Control: no-store
        Pragma: no-cache

        {
          "access_token":"2YotnFZFEjr1zCsicMWpAA",
          "token_type":"example",
          "expires_in":3600,
          "example_parameter":"example_value"
        }


3.3.  Error Response

   If the token request is not valid, such as the access token presented
   does not allow for redelegation, the AS returns an error response as
   described in OAuth2 Core.



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4.  IANA Considerations

   [Registration into the OAuth registry for
   urn:ietf:params:oauth:grant_type:redelegate]

   Note to RFC Editor: this section may be removed on publication as an
   RFC.


5.  Security Considerations

   A resource server engaging in service chaining and token redelegation
   SHOULD request a redelegated token with only the minimum set of
   scopes necessary for calling downstream services.

   A resource server MUST indicate in service documentation the full set
   of scopes required for accessing the full service chain.  A
   redelegation request MUST NOT request escalated privileges without
   involving the resource owner in a new authorization grant.


6.  Acknowledgements

   This work has grown from discussions with Paul Nguyen and Stephen
   Moore, both of MITRE.


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.

7.2.  Informative References

   [InfRef]   "", 2004.


Appendix A.  Standardization of Scopes

   The OAuth2 specification explicitly leaves the definition of scopes
   to the Authorization Server and Protected Resource to agree upon.
   However, in the course of redelegation, it is sometimes desirable to
   have a scope value related to the redelegation permission itself.  It
   is RECOMMENDED to use a scope value of "redelegate" if possible.





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Author's Address

   Justin Richer
   The MITRE Corporation
   202 Burlington Rd.
   Bedford, Massachusetts  01821
   USA

   Phone: +1-781-271-8176
   Fax:
   Email: jricher@mitre.org








































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