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Versions: 00 01

ABFAB                                                           M. Jones
Internet-Draft                                       Bridgewater Systems
Intended status: Informational                             H. Tschofenig
Expires: September 8, 2011                        Nokia Siemens Networks
                                                           March 7, 2011


   The Diameter 'Application Bridging for Federated Access Beyond Web
                          (ABFAB)' Application
                   draft-jones-diameter-abfab-00.txt

Abstract

   The Application Bridging for Federated Access Beyond Web (ABFAB)
   architecture provides cross-domain authentication, authorization and
   accounting functionality by utilizing well-established technologies,
   such as Diameter, the Extensible Authentication Protocol (EAP), and
   the Generic Security Services API (GSS-API).

   This document defines a Diameter application for usage with the ABFAB
   architecture to convey authentication information, and authorization
   decisions from the Diameter server (acting as the identity provider)
   to the Diameter client (acting as a relying party) encoded in a
   Security Assertion Markup Language (SAML) encoding.

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 September 8, 2011.

Copyright Notice

   Copyright (c) 2011 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



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   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.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  6
   3.  Application Identifiers  . . . . . . . . . . . . . . . . . . .  7
   4.  Protocol Description . . . . . . . . . . . . . . . . . . . . .  8
     4.1.  Session Management . . . . . . . . . . . . . . . . . . . .  8
       4.1.1.  Session-Termination-Request  . . . . . . . . . . . . .  9
       4.1.2.  Session-Termination-Answer . . . . . . . . . . . . . .  9
       4.1.3.  Abort-Session-Request  . . . . . . . . . . . . . . . .  9
       4.1.4.  Abort-Session-Answer . . . . . . . . . . . . . . . . .  9
     4.2.  Accounting for ABFAB services  . . . . . . . . . . . . . .  9
       4.2.1.  Accounting-Request . . . . . . . . . . . . . . . . . . 10
       4.2.2.  Accounting-Answer  . . . . . . . . . . . . . . . . . . 10
   5.  Command Codes  . . . . . . . . . . . . . . . . . . . . . . . . 11
     5.1.  Diameter-EAP-Request . . . . . . . . . . . . . . . . . . . 11
     5.2.  Diameter-EAP-Answer  . . . . . . . . . . . . . . . . . . . 12
   6.  AVPs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
   7.  Result-Code AVP Values . . . . . . . . . . . . . . . . . . . . 14
   8.  AVP Occurrence Tables  . . . . . . . . . . . . . . . . . . . . 15
     8.1.  DER, DEA AVP/Command-Code Table  . . . . . . . . . . . . . 15
     8.2.  Coupled Accounting Model AVP Table . . . . . . . . . . . . 15
   9.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 17
     9.1.  AVP Codes  . . . . . . . . . . . . . . . . . . . . . . . . 17
     9.2.  Application Identifier . . . . . . . . . . . . . . . . . . 17
   10. Security Considerations  . . . . . . . . . . . . . . . . . . . 18
   11. Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 19
   12. Normative References . . . . . . . . . . . . . . . . . . . . . 20
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 21












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1.  Introduction

   The Application Bridging for Federated Access Beyond Web (ABFAB)
   architecture [I-D.lear-abfab-arch] provides cross-domain
   authentication, authorization and accounting functionality by
   utilizing well-established technologies, such as Diameter, the
   Extensible Authentication Protocol (EAP), and the Generic Security
   Services API (GSS-API).

   The steps taken generally in an ABFAB federated authentication/
   authorization exchange are as follows:

   1.   Principal provides NAI to Application: Somehow the client is
        configured with at least the realm portion of an NAI, which
        represents the IdP to be discovered.

   2.   Authentication mechanism selection: this is the step necessary
        to indicate that the GSS-EAP SASL/GS2 mechanism will be used for
        authentication/authorization.

   3.   Client Application provides NAI to RP: At the conclusion of
        mechanism selection the NAI must be provided to the RP for
        discovery.

   4.   Discovery of federated IdP: This is discussed in detail below.
        Either the RP is configured with authorized IdPs, or it makes
        use of a federation proxy.

   5.   Request from Relying Party to IdP: Once the RP knows who the IdP
        is, it or its agent will forward RADIUS request that
        encapsulates a GSS/EAP access request to an IdP.  This may or
        may not contain a SAML request as a series of attributes.  At
        this stage, the RP will likely have no idea who the principal
        is.  The RP claims its identity to the IdP in AAA attributes,
        and it makes whatever SAML Attribute Requests through a AAA
        attribute.

   6.   IdP informs the principal of which EAP method to use: The
        available and appropriate methods are discussed below in this
        memo.

   7.   A bunch of EAP messages happen between the endpoints: Messages
        are exchanged between the principal and the IdP until a result
        is determined.  The number and content of those messages will
        depend on the EAP method.  If the IdP is unable to authenticate
        the principal, the process concludes here.  As part of this
        process, the principal will, under protection of EAP, assert the
        identity of the RP to which it intends to authenticate.



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   8.   Successful Authentication: At the very least the IdP (its EAP
        server) and EAP peer / subject have authenticated one another.
        As a result of this step, the subject and the IdP hold two
        cryptographic keys- a Master Session Key (MSK), and an Extended
        MSK (EMSK).  If the asserted identity of the RP by the principal
        matches the identity the RP itself asserted, there is some
        confidence that the RP is now authenticated to the IdP.

   9.   Local IdP Policy Check: At this stage, the IdP checks local
        policy to determine whether the RP and subject are authorized
        for a given transaction/service, and if so, what if any,
        attributes will be released to the RP.  Additional policy checks
        will likely have been made earlier just through the process of
        discovery.

   10.  Response from the IdP to the Relying Party: Once the IdP has
        made a determination of whether and how to authenticate or
        authorize the principal to the RP, it returns either a negative
        AAA result to the RP, or it returns a positive result to the RP,
        along with an optional set of AAA attributes associated with the
        principal that could include one or more SAML assertions.  In
        addition, an EAP MSK is returned to the subject.

   11.  RP Processes Results.  When the RP receives the result from the
        IdP, it should have enough information to either grant or refuse
        a resource access request.  It may have information that leads
        it to make additional attribute queries.  It may have
        information that associates the principal with specific
        authorization identies.  It will apply these results in an
        application-specific way.

   12.  RP returns results to principal: Once the RP has a response it
        must inform the client application of the result.  If all has
        gone well, all are authenticated, and the application proceeds
        with appropriate authorization levels.

   The involved entities are shown in Figure 1.














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                                    +--------------+
                                    |  AAA Server  |
                                    |  (Identity   |
                                    |  Provider)   |
                                    +-^----------^-+
                                      * EAP      | RADIUS/
                                      *          | Diameter
                                    --v----------v--
                                 ///                \\\
                               //                      \\   ***
                              |        Federation        |  back-
                              |                          |  end
                               \\                      //   ***
                                 \\\                ///
                                    --^----------^--
                                      * EAP      | RADIUS/
                    Application       *          | Diameter
   +-------------+  Data            +-v----------v--+
   |             |<---------------->|               |
   | Client      |  EAP/EAP Method  | Server Side   |
   | Application |<****************>| Application   |
   | @ End Host  |  GSS-API         |(Relying Party)|
   |             |<---------------->|               |
   |             |  Application     |               |
   |             |  Protocol        |               |
   |             |<================>|               |
   +-------------+                  +---------------+
                  *** front-end ***

   Legend:

    <****>: End-to-end exchange
    <---->: Hop-by-hop exchange
    <====>: Protocol through which GSS-API/GS2 exchanges are tunnelled

       Figure 1: Architecture for Federated Access of non-Web based
                               Applications














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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 RFC 2119 [RFC2119].

   This document uses terminology defined [I-D.lear-abfab-arch].












































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3.  Application Identifiers

   This specification defines a new Diameter application and the
   respective Application Identifier:


      Diameter ABFAB   (ABFAB)  [[TBD by IANA]]


   The Diameter ABFAB related accounting information generated by the
   Diameter client uses the ABFAB Application Identifier in the case of
   coupled accounting model.  The Diameter Base Accounting Application
   Identifier (value of 3) is used in case of the split accounting
   model.  Refer to Section 4.2 for more information regarding the
   accounting models.




































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4.  Protocol Description


       Relying Party    Client App       IdP

          |              (1)             | Client App gets NAI (somehow)
          |               |              |
          |<-----(2)----->|              | Mechanism Selection
          |               |              |
          |<-----(3)-----<|              | NAI transmitted to RP
          |               |              |
          |<=====(4)====================>| Discovery
          |               |              |
          |>=====(5)====================>| Access request from RP to IdP
          |               |              |
          |               |< - - (6) - -<| EAP method to Principal
          |               |              |
          |               |< - - (7) - ->| EAP Exchange to authenticate
          |               |              | Principal
          |               |              |
          |               |           (8 & 9) Local Policy Check
          |               |              |
          |<====(10)====================<| IdP Assertion to RP
          |               |              |
          |               |              | (11) RP Processes results.
          |               |              |
          |>----(12)----->|              | Results to client app.



        ----- = Between Client App and RP
        ===== = Between RP and IdP
        - - - = Between Client App and IdP




                  Figure 2: Message Interaction Sequence

4.1.  Session Management

   The Diameter server may maintain state or may be stateless.  This is
   indicated in the Auth-Session-State AVP (or its absence).  The
   Diameter client MUST support the Authorization Session State Machine
   defined in [RFC3588].






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4.1.1.  Session-Termination-Request

   The Session-Termination-Request (STR) message [RFC3588] is sent by
   the Diameter client to inform the Diameter server that an authorized
   session is being terminated.

4.1.2.  Session-Termination-Answer

   The Session-Termination-Answer (STA) message [RFC3588] is sent by the
   Diameter server to acknowledge the notification that the session has
   been terminated.

4.1.3.  Abort-Session-Request

   The Abort-Session-Request (ASR) message [RFC3588] is sent by the
   Diameter server to the Diameter client to terminate the authorized
   session.  When the Diameter client receives the ASR message, it MUST
   take further actions to terminate the established application
   context.

4.1.4.  Abort-Session-Answer

   The Abort-Session-Answer (ASA) message [RFC3588] is sent by the Home
   Agent in response to an ASR message.

4.2.  Accounting for ABFAB services

   The Diameter client collects accounting records needed for service
   control and charging MUST support the accounting procedures and the
   Accounting Session State Machine as defined in [RFC3588].

   The Diameter application design guideline
   [I-D.ietf-dime-app-design-guide] defines two separate models for
   accounting:

   Split accounting model:

      According to this model, the accounting messages use the Diameter
      Base Accounting Application Identifier (value of 3).  Since
      accounting is treated as an independent application, accounting
      commands may be routed separately from the rest of application
      messages and thus the accounting messages generally end up in a
      central accounting server.  Since the Diameter ABFAB application
      does not define its own unique accounting commands, this is the
      preferred choice, since it permits use of centralized accounting
      for several applications.





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   Coupled accounting model:

      In this model, the accounting messages will use the ABFAB
      Application Identifiers.  This means that accounting messages will
      be routed like any other Diameter ABFAB application messages.
      This requires the Diameter server in charge of the Diameter ABFAB
      application to handle the accounting records (e.g., sends them to
      a proper accounting server).

   As mentioned above, the preferred choice is to use the split
   accounting model and thus to choose Diameter Base Accounting
   Application Identifier (value of 3) for accounting messages.

4.2.1.  Accounting-Request

   The Accounting-Request command [RFC3588] is sent by the Diameter
   client to the Diameter server to exchange accounting information.

4.2.2.  Accounting-Answer

   The Accounting-Answer command [RFC3588] is sent by the Diameter
   server to the Diameter client to acknowledge an Accounting-Request.





























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5.  Command Codes

   The Diameter ABFAB application defined in this document reuses the
   Diameter EAP application [RFC4072] commands: Diameter-EAP-Request
   (DER) and Diameter-EAP-Answer (DEA).  This specification extends the
   existing DER and DEA command ABNFs to offer the necessary ABFAB
   functionality.  Other than new additional AVPs and the corresponding
   additions to the command ABNFs, the Diameter EAP application command
   ABNFs remain unchanged.  The ABNF language is defined in [RFC3588].


   Command-Name          Abbrev. Code Reference
   ---------------------------------------------
   Diameter-EAP-Request  DER     268  RFC 4072
   Diameter-EAP-Answer   DEA     268  RFC 4072

                          Figure 3: Command Codes

5.1.  Diameter-EAP-Request

   The Diameter-EAP-Request (DER) message, indicated by the Command-Code
   field set to 268 and the 'R' bit set in the Command Flags field, is
   sent by the Diameter client to the Diameter server to initiate a
   Diameter ABFAB authentication and authorization procedure.  The
   Application-ID field of the Diameter Header MUST be set to the
   Diameter ABFAB Application ID (value of TDB).


   <Diameter-EAP-Request> ::= < Diameter Header: 268, REQ, PXY >
                              < Session-Id >
                              { Auth-Application-Id }
                              { Origin-Host }
                              { Origin-Realm }
                              { Destination-Realm }
                              { Auth-Request-Type }
                              [ Destination-Host ]
                              [ NAS-Identifier ]
                              [ NAS-IP-Address ]
                              [ NAS-IPv6-Address ]
                              [ NAS-Port-Type ]
                              [ User-Name ]
                              ...
                              { EAP-Payload }
                              ...
                              [ SAML-AuthnRequest ]
                              ...
                            * [ AVP ]




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   The SAML-AuthnRequest AVP is only included in the first DER message
   send by the Diameter client.  The user is both authenticated and
   during the EAP method authentication.  Authorization happens
   immediately after the authentication procedure has been completed.
   Thus, the Auth-Request-Type AVP MUST be set to the value
   AUTHORIZE_AUTHENTICATE.

5.2.  Diameter-EAP-Answer

   The Diameter-EAP-Answer (DEA) message, indicated by the Command-Code
   field set to 268 and 'R' bit cleared in the Command Flags field, is
   sent in response to the Diameter-EAP-Request message (DER).  The
   Application-Id field in the Diameter message header MUST be set to
   the Diameter ABFAB Application-Id (value of TBD).


   <Diameter-EAP-Answer> ::= < Diameter Header: 268, PXY >
                             < Session-Id >
                             { Auth-Application-Id }
                             { Auth-Request-Type }
                             { Result-Code }
                             { Origin-Host }
                             { Origin-Realm }
                             [ User-Name ]
                             [ EAP-Payload ]
                             [ EAP-Reissued-Payload ]
                             [ EAP-Master-Session-Key ]
                             [ EAP-Key-Name ]
                             [ Multi-Round-Time ]
                             ...
                             [ SAML-AuthnResponse ]
                             [ SAML-Assertion ]
                             ...
                           * [ AVP ]

   SAML related attributes are only included in the final message
   exchange.  Either the SAML-AuthnResponse AVP is included in the
   response or a SAML-Assertion but not both.













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6.  AVPs


                                         +--------------------+
                                         |   AVP Flag rules   |
                                         +----+---+------+----+----+
                        AVP              |    |   |SHOULD|MUST|MAY |
    Attribute Name      Code  Value Type |MUST|MAY| NOT  | NOT|Encr|
   +-------------------------------------+----+---+------+----+----+
   |SAML-Assertion      TBD   UTF8String |    | P |      | V  | Y  |
   +-------------------------------------+----+---+------+----+----+
   |SAML-AuthnRequest   TBD   UTF8String |    | P |      | V  | Y  |
   +-------------------------------------+----+---+------+----+----+
   |SAML-AuthnResponse  TBD   UTF8String |    | P |      | V  | Y  |
   +-------------------------------------+----+---+------+----+----+

                  AVPs for the Diameter ABFAB Application

   [Editor's Note: SAML encryption requirements are FFS.  The "MAY Encr"
   column in the above table refers to XML-Enc rather than the defunct
   Diameter AVP encryption.]

   The SAML-Assertion AVP contains the UTF8String encoded SAML
   assertion.

   The SAML-AuthnRequest AVP contains the UTF8String encoded SAML
   AuthnRequest message.

   The SAML-AuthnResponse AVP contains the UTF8String encoded SAML
   AuthnResponse message.





















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7.  Result-Code AVP Values

   This section defines new Result-Code [RFC3588] values that MUST be
   supported by all Diameter implementations that conform to this
   specification.

   [Editor's Note: ABFAB specific error values may need to be added
   here.]











































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8.  AVP Occurrence Tables

   The following tables present the AVPs defined in this document and
   their occurrences in Diameter messages.

   The table uses the following symbols:

   0:

      The AVP MUST NOT be present in the message.


   0+:

      Zero or more instances of the AVP MAY be present in the message.


   0-1:

      Zero or one instance of the AVP MAY be present in the message.


   1:

      One instance of the AVP MUST be present in the message.

8.1.  DER, DEA AVP/Command-Code Table



                                     +------------+
                                     |Command-Code|
                                     |-----+------+
      AVP Name                       | DER | DEA  |
      -------------------------------|-----+------+
      SAML-Assertion                 |  0  |  1   |
      SAML-AuthnRequest              |  1  |  0   |
      SAML-AuthnResponse             |  0  |  1   |
                                     +-----+------+

   [Editor's Note: Is it possible to return more than one SAML-
   Assertion?]

8.2.  Coupled Accounting Model AVP Table

   The table in this section is used to represent which AVPs defined in
   this document are to be present in the Accounting messages, as
   defined in [RFC3588].



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                                              +-------------+
                                              | Command-Code|
                                              |------+------+
         Attribute Name                       |  ACR |  ACA |
         -------------------------------------|------+------+
         Accounting-Input-Octets              | 0-1  |  0-1 |
         Accounting-Input-Packets             | 0-1  |  0-1 |
         Accounting-Output-Octets             | 0-1  |  0-1 |
         Accounting-Output-Packets            | 0-1  |  0-1 |
         Acct-Multi-Session-Id                | 0-1  |  0-1 |
         Acct-Session-Time                    | 0-1  |  0-1 |
         -------------------------------------|------+------+

   [Editor's Note: Do we need any application specific accounting
   messages for ABFAB?]




































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9.  IANA Considerations

   This section contains the namespaces that have either been created in
   this specification or had their values assigned to existing
   namespaces managed by IANA.

9.1.  AVP Codes

   This specification requires IANA to register the following new AVPs
   from the AVP Code namespace defined in [RFC3588].


   o  SAML-Assertion

   o  SAML-AuthnRequest

   o  SAML-AuthnResponse


   The AVPs are defined in Section 8.

9.2.  Application Identifier

   This specification requires IANA to allocate a new application ID
   from the Application Identifier namespace defined in [RFC3588].


   Application Identifier             | Value
   -----------------------------------+------
   Diameter ABFAB (ABFAB)             | TBD





















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10.  Security Considerations


















































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11.  Acknowledgments


















































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12.  Normative References

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

   [RFC3588]  Calhoun, P., Loughney, J., Guttman, E., Zorn, G., and J.
              Arkko, "Diameter Base Protocol", RFC 3588, September 2003.

   [RFC4072]  Eronen, P., Hiller, T., and G. Zorn, "Diameter Extensible
              Authentication Protocol (EAP) Application", RFC 4072,
              August 2005.

   [I-D.ietf-dime-app-design-guide]
              Fajardo, V., Tschofenig, H., and L. Morand, "Diameter
              Applications Design Guidelines",
              draft-ietf-dime-app-design-guide-12 (work in progress),
              September 2010.

   [I-D.lear-abfab-arch]
              Howlett, J., Hartman, S., Tschofenig, H., and E. Lear,
              "Application Bridging for Federated Access Beyond Web
              (ABFAB) Architecture", draft-lear-abfab-arch-01 (work in
              progress), December 2010.




























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Authors' Addresses

   Mark Jones
   Bridgewater Systems

   Email: mark@azu.ca


   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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