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ABFAB                                                         J. Howlett
Internet-Draft                                                     Janet
Intended status: Informational                                S. Hartman
Expires: May 11, 2014                                  Painless Security
                                                        November 7, 2013


   A RADIUS Attribute, Binding, Profiles, Name Identifier Format, and
                     Confirmation Methods for SAML
                      draft-ietf-abfab-aaa-saml-08

Abstract

   This document describes the use of the Security Assertion Mark-up
   Language (SAML) with RADIUS in the context of the ABFAB architecture.
   It defines two RADIUS attributes, a SAML binding, a SAML name
   identifier format, two SAML profiles, and two SAML confirmation
   methods.  The RADIUS attributes permit encapsulation of SAML
   assertions and protocol messages within RADIUS, allowing SAML
   entities to communicate using the binding.  The two profiles describe
   the application of this binding for ABFAB authentication and
   assertion query/request, enabling a Relying Party to request
   authentication of, or assertions for, user or machine principals.
   These principals may be named using an NAI name identifier format.
   Finally, the subject confirmation methods allow requests and queries
   to be issued for a previously authenticated user or machine without
   needing to explicitly identify them as the subject.  These artifacts
   have been defined to permit application in AAA scenarios other than
   ABFAB, such as network access.

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 May 11, 2014.

Copyright Notice



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   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
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   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.  TODO . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  4
   2.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
   3.  Conventions  . . . . . . . . . . . . . . . . . . . . . . . . .  5
   4.  RADIUS SAML Attributes . . . . . . . . . . . . . . . . . . . .  5
   5.  SAML RADIUS Binding  . . . . . . . . . . . . . . . . . . . . .  6
     5.1.  Required Information . . . . . . . . . . . . . . . . . . .  6
     5.2.  Operation  . . . . . . . . . . . . . . . . . . . . . . . .  6
     5.3.  Processing of names  . . . . . . . . . . . . . . . . . . .  7
       5.3.1.  AAA names  . . . . . . . . . . . . . . . . . . . . . .  8
       5.3.2.  SAML names . . . . . . . . . . . . . . . . . . . . . .  8
       5.3.3.  Use of XML Signatures  . . . . . . . . . . . . . . . .  8
       5.3.4.  Metadata Considerations  . . . . . . . . . . . . . . .  9
   6.  Network Access Identifier Name Identifier Format . . . . . . .  9
   7.  ABFAB Authentication Profile . . . . . . . . . . . . . . . . .  9
     7.1.  Required Information . . . . . . . . . . . . . . . . . . .  9
     7.2.  Profile Overview . . . . . . . . . . . . . . . . . . . . . 10
     7.3.  Profile Description  . . . . . . . . . . . . . . . . . . . 12
       7.3.1.  User Agent Request to Relying Party  . . . . . . . . . 12
       7.3.2.  Relying Party Issues <samlp:AuthnRequest> to
               Identity Provider  . . . . . . . . . . . . . . . . . . 12
       7.3.3.  Identity Provider Identifies Principal . . . . . . . . 12
       7.3.4.  Identity Provider Issues <samlp:Response> to
               Relying Party  . . . . . . . . . . . . . . . . . . . . 13
       7.3.5.  Relying Party Grants or Denies Access to Principal . . 13
     7.4.  Use of Authentication Request Protocol . . . . . . . . . . 13
       7.4.1.  <samlp:AuthnRequest> Usage . . . . . . . . . . . . . . 13
       7.4.2.  <samlp:Response message> Usage . . . . . . . . . . . . 14
       7.4.3.  <samlp:Response Message> Processing Rules  . . . . . . 14
       7.4.4.  Unsolicited Responses  . . . . . . . . . . . . . . . . 15
       7.4.5.  Use of the SAML RADIUS Binding . . . . . . . . . . . . 15
       7.4.6.  Use of XML Signatures  . . . . . . . . . . . . . . . . 15
       7.4.7.  Metadata Considerations  . . . . . . . . . . . . . . . 15
   8.  ABFAB Assertion Query/Request Profile  . . . . . . . . . . . . 15



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     8.1.  Required Information . . . . . . . . . . . . . . . . . . . 16
     8.2.  Profile Overview . . . . . . . . . . . . . . . . . . . . . 16
     8.3.  Profile Description  . . . . . . . . . . . . . . . . . . . 17
       8.3.1.  Differences from the SAML V2.0 Assertion
               Query/Request Profile  . . . . . . . . . . . . . . . . 17
       8.3.2.  Use of the SAML RADIUS Binding . . . . . . . . . . . . 17
       8.3.3.  Use of XML Signatures  . . . . . . . . . . . . . . . . 18
       8.3.4.  Metadata Considerations  . . . . . . . . . . . . . . . 18
   9.  RADIUS State Confirmation Methods  . . . . . . . . . . . . . . 18
   10. Privacy considerations . . . . . . . . . . . . . . . . . . . . 18
   11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 19
   12. Security Considerations  . . . . . . . . . . . . . . . . . . . 19
   13. IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 20
     13.1. RADIUS Attributes  . . . . . . . . . . . . . . . . . . . . 20
     13.2. ABFAB Parameters . . . . . . . . . . . . . . . . . . . . . 20
     13.3. Registration of the ABFAB URN Namespace  . . . . . . . . . 21
   14. References . . . . . . . . . . . . . . . . . . . . . . . . . . 21
     14.1. Normative References . . . . . . . . . . . . . . . . . . . 21
     14.2. Informative References . . . . . . . . . . . . . . . . . . 22
































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1.  TODO

   o  Clean up use of terminology (e.g., "principal") to ensure
      consistency with other ABFAB docs.

   o  Complete the Acknowledgements and Security and Privacy
      Considerations sections.

2.  Introduction

   Within the ABFAB architecture [I-D.ietf-abfab-arch] it is often
   desirable to convey Security Assertion Mark-up Language (SAML)
   asertions and protocol messages.

   SAML typically only considers the use of HTTP-based transports, known
   as bindings [OASIS.saml-bindings-2.0-os], which are primarily
   intended for use with the SAML V2.0 Web Browser Single Sign-On
   Profile [OASIS.saml-profiles-2.0-os].  However the goal of ABFAB is
   to extend the applicability of federated identity beyond the Web to
   other applications by building on the AAA framework.  Consequently
   there exists a requirement for SAML to integrate with the AAA
   framework and protocols such as RADIUS [RFC2865] and Diameter
   [RFC3588], in addition to HTTP.

   A companion specification [I-D.jones-diameter-abfab] specifies
   equivalent funtionality for Diameter.

   In summary this document specifies:

   o  Two RADIUS attributes to encapsulate SAML assertions and protocol
      messages respectively.

   o  A SAML RADIUS binding that defines how SAML assertions and
      protocol messages can be transported by RADIUS within a SAML
      exchange.

   o  A profile of the SAML Authentication Request Protocol that uses
      the SAML RADIUS binding to effect SAML-based authentication and
      authorization.

   o  A profile of the SAML Assertion Query And Request Protocol that
      uses the SAML RADIUS binding to effect the query and request of
      SAML assertions.

   o  Two SAML Subject Confirmation Methods for indicating that a user
      or machine principal is the subject of an assertion.

   This document aspires to the guidelines stipulated by



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   [OASIS.saml-bindings-2.0-os] and [OASIS.saml-profiles-2.0-os] for
   defining new SAML bindings and profiles respectively, and other
   conventions applied formally or otherwise within SAML.  In particular
   where this document provides a 'Required Information' section for the
   binding and profiles that enumerate:

   o  A URI that uniquely identifies the protocol binding or profile

   o  Postal or electronic contact information for the author

   o  A reference to previously defined bindings or profiles that the
      new binding updates or obsoletes

   o  In the case of a profile, any SAML confirmation method identifiers
      defined and/or utilized by the profile

3.  Conventions

   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].

4.  RADIUS SAML Attributes

   The RADIUS SAML binding defined by this binding Section 5 uses two
   attributes to convey SAML assertions and protocol messages
   respectively [OASIS.saml-core-2.0-os] .  Owing to the typical size of
   these structures, these attributes use the Long Extended Type format
   [RFC6929] to encapsulate their data.  The table below defines these
   attributes.  The Length of both of these attributes is >=5.  The More
   and Reserved fields are handled as described in RFC 6929.

   +----------------+------+---------------+---------------------------+
   |      Name      | Type | Extended-Type |           Value           |
   +----------------+------+---------------+---------------------------+
   | SAML-Assertion |  TBD |      TBD      |     One or more octets    |
   |                |      |               | encoding a SAML assertion |
   |  SAML-Message  |  TBD |      TBD      |     One or more octets    |
   |                |      |               |  encoding a SAML protocol |
   |                |      |               |          message          |
   +----------------+------+---------------+---------------------------+

                Table 1: RADIUS SAML attribute definitions








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5.  SAML RADIUS Binding

   The SAML RADIUS binding defines how RADIUS [RFC2865] can be used to
   enable a RADIUS client and server to exchange SAML assertions and
   protocol messages.

5.1.  Required Information

   Identification: urn:ietf:params:abfab:bindings:radius

   Contact information: iesg@ietf.org

   Updates: None.

5.2.  Operation

   RADIUS can be used over multiple underlying transports; this binding
   calls out for the use of Transport Layer Security (TLS) Encryption
   for RADIUS [RFC6614] as REQUIRED to provide interoperability,
   confidentiality, improve integrity protection and support the use of
   longer SAML messages.

   Implementations of this profile can take advantage of other
   mechanisms such as RADIUS packet fragmentation
   [I-D.perez-radext-radius-fragmentation] to permit transport of longer
   SAML messages over UDP-based RADIUS transports, such as those
   described in [RFC2865] and [I-D.ietf-radext-dtls].  Support for
   fragmentation over UDP is not mandatory.

   There are two system models for the use of SAML over RADIUS.  The
   first is a request-response model, using the RADIUS SAML-Message
   attribute defined in Section 4 to encapsulate the SAML protocol
   messages.

   1.  The RADIUS client, acting as a SAML requester, transmits a SAML
       request element within a RADIUS Access-Request message.  This
       message MUST include a single instance of the RADIUS User-Name
       attribute whose value MUST conform to the Network Access
       Identifier [I-D.ietf-radext-nai] scheme.  The SAML requester MUST
       NOT include more than one SAML request element.

   2.  The RADIUS server, acting as a SAML responder, returns a SAML
       protocol message within a RADIUS Access-Accept or Access-Reject
       message.  These messages necessarily conclude a RADIUS exchange
       and therefore this is the only opportunity for the SAML responder
       to send a response in the context of this exchange.  The SAML
       responder MUST NOT include more than one SAML response.  A SAML
       responder that refuses to perform a message exchange with the



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       SAML requester MUST silently discard the SAML request.  This
       often results in a RADIUS access-reject as the same conditions
       that cause the SAML responder to discard the SAML request will
       cause the RADIUS server to fail to authenticate.

   The second system model permits a RADIUS server acting as a SAML
   responder to use the RADIUS SAML-Assertion attribute defined in
   Section 4 to encapsulate an unsolicited, unencrypted SAML assertion.
   This attribute MAY be included in a RADIUS Access-Accept message.
   When included, the attribute MUST contain a single SAML assertion.

   RADIUS servers MUST NOT include both the SAML-Message and the SAML-
   Assertion attribute in the same RADIUS message.  If a SAML responder
   is producing a response to a SAML request, then the first system
   model is used.  A SAML responder MAY ignore a SAML request and send
   an unsolicited assertion using the second system model using the
   RADIUS SAML-Assertion attribute.

   In either system model, SAML responders SHOULD return a RADIUS state
   attribute as part of the Access-Accept message so that future SAML
   queries or requests can be run against the same context of an
   authentication exchange.

   This binding is intended to be composed with other uses of RADIUS,
   such as network access.  Therefore, other arbitrary RADIUS attributes
   MAY be used in either the request or response.

   In the case of a SAML processing error and successful authentication,
   the RADIUS server SHOULD include a SAML-specified <samlp:Status>
   element in the SAML response that is transported within the Access-
   Accept packet sent by the RADIUS server.

   In the case of a SAML processing error and failed authentication, the
   RADIUS server MAY include a SAML-specified <samlp:Status> element in
   the SAML response that is transported within the Access-Reject packet
   sent by the RADIUS server.

5.3.  Processing of names

   SAML entities using profiles of this binding will typically possess
   both the SAML and AAA names of their correspondents.  Frequently
   these entities will need to apply policy using these names; for
   example, when deciding to release attributes.  Often these policies
   will be security-sensitive, and so it is important that policy is
   applied on these names consistently.






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5.3.1.  AAA names

   These rules relate to the processing of AAA names by SAML entities
   using profiles of this binding.

   o  SAML responders SHOULD apply policy based on the NAS identity
      associated with the RADIUS Access-Request.

   o  SAML requesters SHOULD apply policy based on the NAI realm
      associated with the RADIUS Access-Accept.

5.3.2.  SAML names

   These rules relate to the processing of SAML names by SAML entities
   using profiles of this binding.

   SAML issuers MAY apply policy based on the requester's <entityId>
   after validating that the request comes from the NAS.  The following
   methods are sufficient:

   o  NAS identity in trusted digitally signed request.

   o  NAS identity in trusted SAML federation metadata.

   A digitally signed request alone is not sufficient.  A RADIUS entity
   can observe a SAML message and include it in a RADIUS message without
   the concent of the issuer of that SAML message.  If a SAML consumer
   were to process the SAML message without confirming that it applied
   to the RADIUS message, inappropriate policy would be used.

   SAML consumers MAY apply policy based on the SAML issuer's <entityId>
   after validating that the response comes from the RADIUS server.  The
   following methods are sufficient:

   o  RADIUS realm in trusted digitally signed request.

   o  RADIUS realm in trusted SAML federation metadata.

   A digitally signed request alone is not sufficient.

5.3.3.  Use of XML Signatures

   This bindings calls for the use of SAML elements that support XML
   signatures.  To promote interoperability implementations of this
   binding MUST support a default configuration that does not require
   the use of XML signatures.  Implementations MAY choose to use XML
   signatures, but this usage is outside of the scope of this binding.




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5.3.4.  Metadata Considerations

   There are no metadata considerations particular to this binding,
   because this binding and profiles of this binding are intended to be
   used without metadata.  In this usage, RADIUS infrastructure is used
   to provide integrity and naming.  RADIUS configuration is used to
   provide policy including which attributes are accepted from a SAML
   responder and which attributes are sent by a SAML responder.

   Implementations MAY support other configurations including the use of
   metadata.

6.  Network Access Identifier Name Identifier Format

   URI: urn:ietf:params:abfab:nameid-format:nai

   Indicates that the content of the element is in the form of a Network
   Access Identifier (NAI) using the syntax described by
   [I-D.ietf-radext-nai].

7.  ABFAB Authentication Profile

   In the scenario supported by the ABFAB Authentication Profile, a
   Principal controlling a User Agent requests access to a Relying
   Party.  The User Agent and Relying Party uses RADIUS to authenticate
   the Principal.  The Relying Party, acting as a NAS, attempts to
   validate the Principal's credentials against a RADIUS server acting
   the Principal's Identity Provider.  If the Identity Provider
   successfully authenticates the Principal, it produces an
   authentication assertion which is consumed by the Relying Party.
   During this process, a name identifier might also be established
   between the Relying Party and the Identity Provider.

7.1.  Required Information

   Identification: urn:ietf:params:abfab:profiles:authentication

   Contact information: iesg@ietf.org

   SAML Confirmation Method Identifiers: The SAML V2.0 "sender vouches"
   confirmation method identifier,
   urn:oasis:names:tc:SAML:2.0:cm:sender-vouches, is used by this
   profile.

   Updates: None.






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7.2.  Profile Overview

   To implement this scenario a profile of the SAML Authentication
   Request protocol is used in conjuction with the SAML RADIUS binding
   defined in Section 5.

   This profile is based on the SAML V2.0 Web Browser Single Sign-On
   Profile [OASIS.saml-profiles-2.0-os].  There are some important
   differences, specifically:

   Authentication:  This profile does not require the use of any
      particular authentication method.  The ABFAB architecture does
      require the use of EAP [RFC3579], but this specification may be
      used in other non-ABFAB scenarios.

   Bindings:  This profile does not require the use of HTTP-based
      bindings.  Instead all SAML protocol messages are transported
      using the SAML RADIUS binding defined in Section 5.  This is
      intended to reduce the number of bindings that implementations
      must support to be interoperable.

   Requests:  The profile does not permit the Relying Party to name the
      <saml:Subject> of the <samlp:AuthnRequest>.  This is intended to
      simplify implementation and interoperability.

   Responses:  The profile only permits the Identity Provider to return
      a single assertion that must contain exactly one authentication
      statement.  Other statements may be included within this assertion
      at the discretion of the Identity Provider.  This is intended to
      simplify implementation and interoperability.





















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   Figure 1 below illustrates the flow of messages within this profile.

     User Agent          Relying Party             Identity Provider
         |                     |                           |
         |         (1)         |                           |
         | - - - - - - - - - > |                           |
         |                     |                           |
         |                     |            (2)            |
         |                     | - - - - - - - - - - - - > |
         |                     |                           |
         |              (3)    |                           |
         | < - - - - - - - - - |- - - - - - - - - - - - -> |
         |                     |                           |
         |                     |            (4)            |
         |                     | < - - - - - - - - - - - - |
         |                     |                           |
         |         (5)         |                           |
         | < - - - - - - - - - |                           |
         |                     |                           |
         V                     V                           V

   The following steps are described by the profile.  Within an
   individual step, there may be one or more actual message exchanges.

                                 Figure 1

   1.  User Agent Request to Relying Party (Section 7.3.1): In step 1,
       the Principal, via a User Agent, makes a request for a secured
       resource at the Relying Party.  The Relying Party determines that
       no security context for the User Agent exists and initiates
       authentication of the Principal.

   2.  Relying Party Issues <samlp:AuthnRequest> to Identity Provider
       (Section 7.3.2).  In step 2, the Relying Party may optionally
       issue a <samlp:AuthnRequest> message to be delivered to the
       Identity Provider using the SAML RADIUS binding.

   3.  Identity Provider Identifies Principal (Section 7.3.3).  In step
       3, the Principal is authenticated and identified by the Identity
       Provider, while honoring any requirements imposed by the Relying
       Party in the <samlp:AuthnRequest> message if provided.

   4.  Identity Provider Issues <samlp:Response> to Relying Party
       (Section 7.3.4).  In step 4, the Identity Provider issues a
       <samlp:Response> message to the Relying Party using the SAML
       RADIUS binding.  The response either indicates an error or
       includes an authentication statement in exactly one assertion.




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   5.  Relying Party Grants or Denies Access to Principal
       (Section 7.3.5).  In step 5, having received the response from
       the Identity Provider, the Relying Party can respond to the
       Principal's User Agent with its own error, or can establish its
       own security context for the Principal and return the requested
       resource.

7.3.  Profile Description

   The ABFAB Authentication Profile is a profile of the SAML V2.0
   Authentication Request Protocol [OASIS.saml-core-2.0-os].  Where this
   specification conflicts with Core, the former takes precedence.

7.3.1.  User Agent Request to Relying Party

   The profile is initiated by an arbitrary User Agent request to the
   Relying Party.  There are no restrictions on the form of the request.
   The Relying Party is free to use any means it wishes to associate the
   subsequent interactions with the original request.  The Relying
   Party, acting as a NAS, attempts to authenticate the User Agent.

7.3.2.  Relying Party Issues <samlp:AuthnRequest> to Identity Provider

   The Relying Party uses RADIUS to communicate with the Principal's
   Identity Provider.  The Relying Party MAY include a <samlp:
   AuthnRequest> within this RADIUS Access-Request message using the
   SAML RADIUS binding.  The next hop destination MAY be the Identity
   Provider or alternatively an intermediate RADIUS proxy.

   Profile-specific rules for the contents of the <samlp:AuthnRequest>
   element are given in Section 7.4.1.

7.3.3.  Identity Provider Identifies Principal

   The Identity Provider MUST establish the identity of the Principal
   using RADIUS authentication, or else it will return an error.  If the
   ForceAuthn attribute on the <samlp:AuthnRequest> element (if sent by
   the requester) is present and true, the Identity Provider MUST
   freshly establish this identity rather than relying on any existing
   session state it may have with the Principal (for example, TLS state
   that may be used for session resumption).  Otherwise, and in all
   other respects, the Identity Provider may use any method to
   authenticate the Principal, subject to the constraints called out in
   the <samlp:AuthnRequest> message.







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7.3.4.  Identity Provider Issues <samlp:Response> to Relying Party

   The Identity Provider MUST conclude the authentication in a manner
   consistent with the RADIUS authentication result, and MAY issue a
   <samlp:Response> message to the Relying Party consisent with the
   authentication result and as described in [OASIS.saml-core-2.0-os]
   and delivered to the Relying Party using the SAML RADIUS binding.

   Profile-specific rules regarding the contents of the <samlp:Response>
   element are given in Section 7.4.2.

7.3.5.  Relying Party Grants or Denies Access to Principal

   If issued by the Identity Provider, the Relying Party MUST process
   the <samlp:Response> message and any enclosed <saml:Assertion>
   elements as described in [OASIS.saml-core-2.0-os].  Any subsequent
   use of the <saml:Assertion> elements is at the discretion of the
   Relying Party, subject to any restrictions on use contained within
   the assertions themselves or previously established out-of-band
   policy governing interactions between the Identity Provider and the
   Relying Party.

7.4.  Use of Authentication Request Protocol

   This profile is based on the Authentication Request Protocol defined
   in [OASIS.saml-core-2.0-os].  In the nomenclature of actors
   enumerated in section 3.4, the Relying Party is the requester, the
   User Agent is the attesting entity and the Principal is the Requested
   Subject.

7.4.1.  <samlp:AuthnRequest> Usage

   The Relying Party MUST NOT include a <saml:Subject> element in the
   request.  The authenticated RADIUS user identifies the principal to
   the Identity Provider.

   A Relying Party MAY include any message content described in
   [OASIS.saml-core-2.0-os], section 3.4.1.  All processing rules are as
   defined in [OASIS.saml-core-2.0-os].

   If the Relying Party wishes to permit the Identity Provider to
   establish a new identifier for the principal if none exists, it MUST
   include a <saml:NameIDPolicy> element with the AllowCreate attribute
   set to "true".  Otherwise, only a principal for whom the Identity
   Provider has previously established an identifier usable by the
   Relying Party can be authenticated successfully.

   The <samlp:AuthnRequest> message MAY be signed.  Authentication and



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   integrity are also provided by the RADIUS SAML binding.

7.4.2.  <samlp:Response message> Usage

   If the Identity Provider cannot or will not satisfy the request, it
   MAY respond with a <samlp:Response> message containing an appropriate
   error status code or codes.

   If the Identity Provider wishes to return an error, it MUST NOT
   include any assertions in the <samlp:Response message>.  Otherwise,
   if the request is successful (or if the response is not associated
   with a request), the <samlp:Response> element MUST conform to the
   following:

   o  It MAY be signed.

   o  It MUST contain exactly one <saml:Assertion>.  The <saml:Subject>
      element of this assertion MUST refer to the authenticated RADIUS
      user.

   o  The assertion MUST contain a <saml:AuthnStatement>.  This MUST
      contain a <saml:Subject> element with at least one <saml:
      SubjectConfirmation> element containing a Method of
      urn:oasis:names:tc:SAML:2.0:cm:sender-vouches that reflects the
      authentication of the Principal to the Identity Provider.  If the
      containing message is in response to an <samlp:AuthnRequest>, then
      the InResponseTo attribute MUST match the request's ID.

   o  Other conditions MAY be included as requested by the Relying Party
      or at the discretion of the Identity Provider.  The Identity
      Provider is NOT obligated to honor the requested set of conditions
      in the <samlp:AuthnRequest>, if any.

7.4.3.  <samlp:Response Message> Processing Rules

   The Relying Party MUST do the following:

   o  Assume that the principal implied by a SAML <Subject> element, if
      present, takes precedence over a principal implied by the RADIUS
      User-Name attribute.

   o  Verify that the InResponseTo attribute in the sender-vouches
      <saml:SubjectConfirmationData> equals the ID of its original
      <samlp:AuthnRequest> message, unless the response is unsolicited,
      in which case the attribute MUST NOT be present.

   o  If a <saml:AuthnStatement> used to establish a security context
      for the Principal contains a SessionNotOnOrAfter attribute, the



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      security context SHOULD be discarded once this time is reached,
      unless the service provider reestablishes the Principal's identity
      by repeating the use of this profile.

   o  Verify that any assertions relied upon are valid according to
      processing rules in [OASIS.saml-core-2.0-os].

   o  Any assertion which is not valid, or whose subject confirmation
      requirements cannot be met MUST be discarded and MUST NOT be used
      to establish a security context for the Principal.

7.4.4.  Unsolicited Responses

   An Identity Provider MAY initiate this profile by delivering an
   unsolicited <saml:Assertion> to a Relying Party.  This MUST NOT
   contain any sender-vouches <saml:SubjectConfirmationData> elements
   containing an InResponseTo attribute.

7.4.5.  Use of the SAML RADIUS Binding

   It is RECOMMENDED that the RADIUS exchange is protected using TLS
   encryption for RADIUS [RFC6614] to provide confidentiality and
   improve integrity protection.

7.4.6.  Use of XML Signatures

   This profile calls for the use of SAML elements that support XML
   signatures.  To promote interoperability implementations of this
   profile MUST NOT require the use of XML signatures.  Implementations
   MAY choose to use XML signatures, but this usage is outside of the
   scope of this profile.

7.4.7.  Metadata Considerations

   There are no metadata considerations particular to this binding.

8.  ABFAB Assertion Query/Request Profile

   This profile builds on the SAML V2.0 Assertion Query/Request Profile
   defined by [OASIS.saml-profiles-2.0-os].  That profile describes the
   use of the Assertion Query and Request Protocol defined by section
   3.3 of [OASIS.saml-core-2.0-os] with synchronous bindings, such as
   the SOAP binding defined in [OASIS.saml-bindings-2.0-os] or the SAML
   RADIUS binding defined elsewhere in this document.

   While the SAML V2.0 Assertion Query/Request Profile is independent of
   the underlying binding, it is nonetheless useful to describe the use
   of this profile with the SAML RADIUS binding in the interests of



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   promoting interoperable implementations, particularly as the SAML
   V2.0 Assertion Query/Request Profile is most frequently discussed and
   implemented in the context of the SOAP binding.

8.1.  Required Information

   Identification: urn:ietf:params:abfab:profiles:query

   Contact information: iesg@ietf.org

   Description: Given below.

   Updates: None.

8.2.  Profile Overview

   As with the SAML V2.0 Assertion Query/Request Profile defined by
   [OASIS.saml-profiles-2.0-os] the message exchange and basic
   processing rules that govern this profile are largely defined by
   Section 3.3 of [OASIS.saml-core-2.0-os] that defines the messages to
   be exchanged, in combination with the binding used to exchange the
   messages.  The SAML RADIUS binding described in this document defines
   the binding of the message exchange to RADIUS.  Unless specifically
   noted here, all requirements defined in those specifications apply.

   Figure 2 below illustrates the basic template for the query/request
   profile.

     SAML Requester                                  SAML Authority
         |                                                 |
         |                       (1)                       |
         | - - - - - - - - - - - - - - - - - - - - - - - > |
         |                                                 |
         |                       (2)                       |
         | < - - - - - - - - - - - - - - - - - - - - - - - |
         |                                                 |
         |                                                 |
         V                                                 V

   The following steps are described by the profile.

                                 Figure 2

   1.  Query/Request issued by SAML Requester: In step 1, a SAML
       requester initiates the profile by sending an
       <AssertionIDRequest>, <SubjectQuery>, <AuthnQuery>,
       <AttributeQuery>, or <AuthzDecisionQuery> message to a SAML
       authority.



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   2.  <Response> issued by SAML Authority: In step 2, the responding
       SAML authority (after processing the query or request) issues a
       <Response> message to the SAML requester.

8.3.  Profile Description

8.3.1.  Differences from the SAML V2.0 Assertion Query/Request Profile

   This profile is identical to the SAML V2.0 Assertion Query/Request
   Profile, with the following exceptions:

   o  When processing the SAML request, the SAML responder MUST give
      precedence to the principal implied by RADIUS State attribute, if
      present, over the principal implied by the SAML request's
      <Subject>, if any.

   o  In respect to section 6.3.1 and 6.5, this profile does not
      consider the use of metadata (as in [OASIS.saml-metadata-2.0-os]);
      see Section 8.3.4.

   o  In respect to sections 6.3.2, 6.4.1 and 6.4.2, this profile
      additionally stipulates that implementations of this profile MUST
      NOT require the use of XML signatures; see Section 8.3.3.

8.3.2.  Use of the SAML RADIUS Binding

   The RADIUS Access-Request sent by the SAML requester:

   o  MUST use a RADIUS User-Name attribute whose value is "@REALM",
      where REALM is the destination NAI realm.

   o  MUST include an instance of the RADIUS Service-Type attribute,
      having a value of Authorize-Only.

   o  SHOULD include the RADIUS State attribute, where this Query/
      Request pertains to previously authenticated principal.

   When processing the SAML request, the SAML responder MUST give
   precedence to the principal implied by RADIUS State attribute over
   the principal implied by the SAML request's <Subject>, if any.

   It is RECOMMENDED that the RADIUS exchange is protected using TLS
   encryption for RADIUS [RFC6614] to provide confidentiality and
   improve integrity protection.







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8.3.3.  Use of XML Signatures

   This profile calls for the use of SAML elements that support XML
   signatures.  To promote interoperability implementations of this
   profile MUST NOT require the use of XML signatures.  Implementations
   MAY choose to use XML signatures, but this usage is outside of the
   scope of this profile.

8.3.4.  Metadata Considerations

   There are no metadata considerations particular to this binding.

9.  RADIUS State Confirmation Methods

   URI: urn:ietf:params:abfab:cm:user

   URI: urn:ietf:params:abfab:cm:machine

   The RADIUS State Confirmation Methods indicate that the Subject is
   the system entity (either the user or machine) authenticated by a
   previously transmitted RADIUS Access-Accept message, as identified by
   the value of that RADIUS message's State attribute, in the sense of
   [I-D.ietf-emu-eap-tunnel-method].

10.  Privacy considerations

   The profiles defined in this document allow a SAML requester to
   request specific information about the principal and allow a SAML
   responder to disclose information about a requester.  Responders MUST
   apply policy to decide what information is released.  The SAML
   requester does not typically know the identity of the principal
   unless informed by the SAML responder or RADIUS server.  The SAML
   requester does typically know the realm of the IDP.  Information that
   is released MAY include generic attributes such as affiliation shared
   by many principals.  Even these generic attributes can help to
   identify a specific principal.  Other attributes MAY provide a SAML
   requester with the ability to link the same principals between
   sessions with the same SAML requester.  Other attributes MAY provide
   the requester with the ability to link the principal between
   requesters or with personally identifyable information about the
   principal.

   These profiles do not directly provide a principal with a mechanism
   to express preferences about what information is released.  That
   information can be expressed out-of-band, for example as part of
   enrollment.

   The SAML requester MAY disclose privacy-sensitive information about



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   itself as part of the request.  This is unlikely in typical
   deployments.

   If RADIUS proxies are used, then attributes disclode by the SAML
   responder are visible to the proxies.  This is a significant privacy
   exposure in some deployments.  Ongoing work is exploring mechanisms
   for creating TLS connections directly between the NAS and the RADIUS
   server to reduce this exposure.  If proxies are used, the impact of
   exposing SAML assertions to the proxies needs to be carefully
   considered.

   The use of TLS to provide confidentiality for the RADIUS exchange is
   strongly encouraged.  Without this, passive observers can observe the
   assertions.

11.  Acknowledgements

   TODO: Need to acknowledge OASIS SSTC, UoMurcia, Scott, Jim, and
   Steven.

12.  Security Considerations

   TODO: Elaborate on the following

   The RADIUS server vouches for its SAML messages.  The NAS trusts any
   statement in the SAML messages from the RADIUS server in the same way
   that it trusts information contained in RADIUS attributes.  The NAS
   MUST apply policy and filter the information based on what
   information the RADIUS server is permitted to assert and on what
   trust is reasonable to place in proxies between the NAS and RADIUS
   server.

   SAML entities' level of trust in the SAML messages that they recieve
   from other entities should be consistent with the trust it holds in
   the RADIUS infrastructure.  That is SAML entities SHOULD trust RADIUS
   to authenticate the principal and to reach the right IDP.  SAML
   entities trust the RADIUS infrastructure to provide integrity of the
   SAML messages.  However policy MUST be applied to limit what
   statements are permitted.

   XML signatures and encryption are provided as an OPTIONAL mechanism
   for end-to-end security.  These mechanism can protect SAML messages
   from being modified by proxies in the RADIUS infrastructure.  These
   mechanisms are not mandatory-to-implement.  It is believed that
   ongoing work to provide direct TLS connections between a NAS and
   RADIUS server will provide similar assurances but better
   deployability.  XML security is appropriate for deployments where
   end-to-end security is required but proxies cannot be removed or



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   where SAML messages need to be verified at a later time ro by parties
   not involved in the authentication exchange.

13.  IANA Considerations

13.1.  RADIUS Attributes

   Assignments of additional enumerated values for the RADIUS attribute
   defined in this document are to be processed as described in
   [RFC6929], subject to the additional requirements of a published
   specification.

13.2.  ABFAB Parameters

   A new top-level registry is created titled "ABFAB Parameters".

   In this top-level registry, a sub-registry titled "ABFAB URN
   Parameters" is created.  Registration in this registry is by the IETF
   review or expert review procedures [RFC5226].

   This paragraph gives guidance to designated experts.  Registrations
   in this registry are generally only expected as part of protocols
   published as RFCs on the IETF stream; other URIs are expected to be
   better choices for non-IETF work.  Expert review is permitted mainly
   to permit early registration related to specifications under
   development when the community believes they have reach sufficient
   maturity.  The expert SHOULD evaluate the maturity and stability of
   such an IETF-stream specification.  Experts SHOULD review anything
   not from the IETF stream for consistency and consensus with current
   practice.  Today such requests would not typically be approved.

   If the "paramname" parameter is registered in this registry then its
   URN will be "urn:ietf:params:abfab:paramname".  The initial
   registrations are as follows:

                  +-------------------------+-----------+
                  | Parameter               | Reference |
                  +-------------------------+-----------+
                  | bindings:radius         | Section 5 |
                  | nameid-format:nai       | Section 6 |
                  | profiles:authentication | Section 7 |
                  | profiles:query          | Section 8 |
                  | cm:user                 | Section 9 |
                  | cm:machine              | Section 9 |
                  +-------------------------+-----------+

                             ABFAB Parameters




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13.3.  Registration of the ABFAB URN Namespace

   IANA is requested to register the "abfab" URN sub-namespace in the
   IETF URN sub-namespace for protocol parameters defined in [RFC3553].

   Registry Name: abfab

   Specification: draft-ietf-abfab-aaa-saml

   Repository: ABFAB URN Parameters (Section Section 13.2)

   Index Value: Sub-parameters MUST be specified in UTF-8 using standard
   URI encoding where necessary.

14.  References

14.1.  Normative References

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

   [RFC2865]                                Rigney, C., Willens, S.,
                                            Rubens, A., and W. Simpson,
                                            "Remote Authentication Dial
                                            In User Service (RADIUS)",
                                            RFC 2865, June 2000.

   [RFC3579]                                Aboba, B. and P. Calhoun,
                                            "RADIUS (Remote
                                            Authentication Dial In User
                                            Service) Support For
                                            Extensible Authentication
                                            Protocol (EAP)", RFC 3579,
                                            September 2003.

   [RFC6614]                                Winter, S., McCauley, M.,
                                            Venaas, S., and K. Wierenga,
                                            "Transport Layer Security
                                            (TLS) Encryption for
                                            RADIUS", RFC 6614, May 2012.

   [RFC6929]                                DeKok, A. and A. Lior,
                                            "Remote Authentication Dial
                                            In User Service (RADIUS)
                                            Protocol Extensions",
                                            RFC 6929, April 2013.



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   [I-D.ietf-radext-nai]                    DeKok, A., "The Network
                                            Access Identifier",
                                            draft-ietf-radext-nai-03
                                            (work in progress),
                                            May 2013.

   [OASIS.saml-bindings-2.0-os]             Cantor, S., Hirsch, F.,
                                            Kemp, J., Philpott, R., and
                                            E. Maler, "Bindings for the
                                            OASIS Security Assertion
                                            Markup Language (SAML)
                                            V2.0", OASIS Standard saml-
                                            bindings-2.0-os, March 2005.

   [OASIS.saml-core-2.0-os]                 Cantor, S., Kemp, J.,
                                            Philpott, R., and E. Maler,
                                            "Assertions and Protocol for
                                            the OASIS Security Assertion
                                            Markup Language (SAML)
                                            V2.0", OASIS Standard saml-
                                            core-2.0-os, March 2005.

   [OASIS.saml-profiles-2.0-os]             Hughes, J., Cantor, S.,
                                            Hodges, J., Hirsch, F.,
                                            Mishra, P., Philpott, R.,
                                            and E. Maler, "Profiles for
                                            the OASIS Security Assertion
                                            Markup Language (SAML)
                                            V2.0", OASIS Standard OASIS.
                                            saml-profiles-2.0-os,
                                            March 2005.

   [OASIS.saml-metadata-2.0-os]             Cantor, S., Moreh, J.,
                                            Philpott, R., and E. Maler,
                                            "Metadata for the Security
                                            Assertion Markup Language
                                            (SAML) V2.0", OASIS Standard
                                             saml-metadata-2.0-os,
                                            March 2005.

14.2.  Informative References

   [RFC3553]                                Mealling, M., Masinter, L.,
                                            Hardie, T., and G. Klyne,
                                            "An IETF URN Sub-namespace
                                            for Registered Protocol
                                            Parameters", BCP 73,
                                            RFC 3553, June 2003.



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   [RFC3575]                                Aboba, B., "IANA
                                            Considerations for RADIUS
                                            (Remote Authentication Dial
                                            In User Service)", RFC 3575,
                                            July 2003.

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

   [RFC5226]                                Narten, T. and H.
                                            Alvestrand, "Guidelines for
                                            Writing an IANA
                                            Considerations Section in
                                            RFCs", BCP 26, RFC 5226,
                                            May 2008.

   [I-D.perez-radext-radius-fragmentation]  Perez-Mendez, A., Lopez, R.,
                                            Pereniguez-Garcia, F.,
                                            Lopez-Millan, G., Lopez, D.,
                                            and A. DeKok, "Support of
                                            fragmentation of RADIUS
                                            packets", draft-perez-
                                            radext-radius-fragmentation-
                                            01 (work in progress),
                                            February 2012.

   [I-D.jones-diameter-abfab]               Jones, M. and H. Tschofenig,
                                            "The Diameter 'Application
                                            Bridging for Federated
                                            Access Beyond Web (ABFAB)'
                                            Application", draft-jones-
                                            diameter-abfab-00 (work in
                                            progress), March 2011.

   [I-D.ietf-abfab-arch]                    Howlett, J., Hartman, S.,
                                            Tschofenig, H., Lear, E.,
                                            and J. Schaad, "Application
                                            Bridging for Federated
                                            Access Beyond Web (ABFAB)
                                            Architecture",
                                            draft-ietf-abfab-arch-03
                                            (work in progress),
                                            July 2012.

   [I-D.ietf-radext-dtls]                   DeKok, A., "DTLS as a



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                                            Transport Layer for RADIUS",
                                            draft-ietf-radext-dtls-05
                                            (work in progress),
                                            April 2013.

   [I-D.ietf-emu-eap-tunnel-method]         Zhou, H., Cam-Winget, N.,
                                            Salowey, J., and S. Hanna,
                                            "Tunnel EAP Method (TEAP)
                                            Version 1", draft-ietf-emu-
                                            eap-tunnel-method-06 (work
                                            in progress), March 2013.

Authors' Addresses

   Josh Howlett
   Janet
   Lumen House, Library Avenue, Harwell
   Oxford  OX11 0SG
   UK

   Phone: +44 1235 822363
   EMail: Josh.Howlett@ja.net


   Sam Hartman
   Painless Security


   Phone:
   EMail: hartmans-ietf@mit.edu





















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