ABFAB J. Howlett Internet-Draft JANET(UK) Intended status: Informational S. Hartman Expires: May 3, 2012 Painless Security October 31, 2011 A RADIUS Attribute, Binding and Profiles for SAML draft-ietf-abfab-aaa-saml-02 Abstract This document specifies a RADIUS attribute, binding and two profiles for the Security Assertion Mark-up Language (SAML). The attribute provides RADIUS encapsulation of SAML protocol messages, while the binding describes the transport of this attribute, and the SAML protocol messages within, using RADIUS. The profiles describe the application of this binding for Abfab authentication and assertion query/request. The SAML RADIUS attribute and binding are defined generically to permit application in other scenarios, 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 3, 2012. 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 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 Howlett & Hartman Expires May 3, 2012 [Page 1] Internet-Draft SAML RADIUS October 2011 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. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 4 3. RADIUS SAML-Message Attribute . . . . . . . . . . . . . . . . 4 4. SAML RADIUS Binding . . . . . . . . . . . . . . . . . . . . . 5 4.1. Required Information . . . . . . . . . . . . . . . . . . . 5 4.2. Operation . . . . . . . . . . . . . . . . . . . . . . . . 5 4.2.1. Metadata Considerations . . . . . . . . . . . . . . . 6 5. Abfab Authentication Profile . . . . . . . . . . . . . . . . . 6 5.1. Required Information . . . . . . . . . . . . . . . . . . . 6 5.2. Profile Overview . . . . . . . . . . . . . . . . . . . . . 7 5.3. Profile Description . . . . . . . . . . . . . . . . . . . 9 5.3.1. User Agent Request to Relying Party . . . . . . . . . 9 5.3.2. Relying Party Issues to Identity Provider . . . . . . . . . . . . . . . . . . 9 5.3.3. Identity Provider Identifies Principal . . . . . . . . 9 5.3.4. Identity Provider Issues to Relying Party . . . . . . . . . . . . . . . . . . . . 10 5.3.5. Relying Party Grants or Denies Access to Principal . . 10 5.4. Use of Authentication Request Protocol . . . . . . . . . . 10 5.4.1. Usage . . . . . . . . . . . . . . 10 5.4.2. Usage . . . . . . . . . . . . 11 5.4.3. samlp:Response Message Processing Rules . . . . . . . 12 5.4.4. Unsolicited Responses . . . . . . . . . . . . . . . . 12 5.4.5. Use of the SAML RADIUS Binding . . . . . . . . . . . . 12 5.4.6. Metadata Considerations . . . . . . . . . . . . . . . 12 6. Abfab Assertion Query/Request Profile . . . . . . . . . . . . 12 7. Security Considerations . . . . . . . . . . . . . . . . . . . 13 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 13 9.1. Normative References . . . . . . . . . . . . . . . . . . . 13 9.2. Informative References . . . . . . . . . . . . . . . . . . 14 Howlett & Hartman Expires May 3, 2012 [Page 2] Internet-Draft SAML RADIUS October 2011 1. Introduction The SAML RADIUS attribute, binding and profiles are motivated by the requirements of the Abfab architecture [I-D.lear-abfab-arch]. In this architecture, it is often desirable to convey Security Assertion Mark-up Language (SAML) protocol messages between a SAML requester and SAML responder; for example, to allow a Relying Party to obtain a SAML assertion containing attributes that describe a principal. SAML [OASIS.saml-core-2.0-os] defines a number of SAML protocol messages that are used for a range of different purposes [OASIS.saml-profiles-2.0-os]. These messages are derived from common request and reponse abstract types. These request and response protocol messages can be exchanged using a variety of underlying transport protocols, such as HTTP. In the SAML model, the means by which a SAML protocol message exchange is framed over an underlying transport protocol is known as a SAML 'binding'. SAML already defines [OASIS.saml-bindings-2.0-os] a number of mainly HTTP-based bindings; these principally use HTTP as the underlying transport protocol, generally for use with the SAML 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 application protocols by building on the AAA framework. Consequently here exists a requirement for an AAA-based binding, that is functionally equivalent to the existing bindings, that uses the RADIUS [RFC2865] and Diameter [RFC3588] protocols, rather than HTTP. This document defines a new RADIUS-based SAML binding, building on a SAML RADIUS attribute also defined by this document. This attribute and binding are likely to be useful for purposes besides Abfab; an example of one potential application is SAML-based authorisation for network access. The attribute and binding are therefore defined generically to facilitate general applicability. Nonetheless it is useful to also define how the SAML RADIUS binding should be used for Abfab-specific purposes to facilitate interoperability. This document therefore also define two profiles of this binding to support authentication and assertion request. To summarise, this document specifies: o A SAML RADIUS attribute that defines how to encapsulate a SAML protocol message within a RADIUS attribute. o A SAML RADIUS binding that defines how SAML requesters and responders can exchange SAML protocol messages. Howlett & Hartman Expires May 3, 2012 [Page 3] Internet-Draft SAML RADIUS October 2011 o The Abfab Authentication Profile that defines how the SAML RADIUS binding is used to effect SAML-based authentication and authorisation within the Abfab architecture. o The Abfab Assertion Request Profile that defines how the SAML RADIUS binding is used to effect SAML-based assertion request within the Abfab architecture. The RADIUS SAML binding and profile specifications aspire to adhere to the guidelines stipulated by [OASIS.saml-bindings-2.0-os] and [OASIS.saml-profiles-2.0-os] respectively. To this end, the binding and profiles provide a 'Required Information' section that enumerates: 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. 2. 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]. 3. RADIUS SAML-Message Attribute This attribute contains a SAML [OASIS.saml-core-2.0-os] protocol message. Where multiple SAML-Message attributes are included in a RADIUS message, the Message fields of these attributes are to be concatenated to form a single SAML message. A summary of the SAML-Message format is shown below. The fields are transmitted from left to right. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | SAML Message... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 1 Howlett & Hartman Expires May 3, 2012 [Page 4] Internet-Draft SAML RADIUS October 2011 Type: TBD Length: >=4 Message: The Message field is one or more octets containing a SAML message. If larger than a single attribute, the SAML message data MUST be split on 253-octet boundaries over as many attributes as necessary. The SAML message is reconstructed by concatenating the contents of all SAML-Message attributes. TODO: request a new RADIUS attribute 4. SAML RADIUS Binding The SAML RADIUS binding defines how RADIUS [RFC2865] can be used to enable a RADIUS client and server to exchange SAML protocol messages. 4.1. Required Information Identification: TBD Contact information: TBD Updates: None. 4.2. Operation RADIUS can be used over multiple underlying transports; this binding calls out the use of RADIUS over UDP as REQUIRED. It is RECOMMENDED that the RADIUS exchange is protected using TLS encryption for RADIUS [I-D.ietf-radext-radsec] to provide confidentiality and improve integrity protection. The system model used for SAML conversations over RADIUS is a simple request-response model, using the RADIUS SAML-Message attribute defined in Section 3 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 [RFC4282] scheme. The NAI SHOULD be used to route the message towards the SAML responder, which MAY be more than one RADIUS hop distant. The SAML requester MUST NOT include more than one SAML request element. 2. The RADIUS server, acting as a SAML responder, MAY return a SAML protocol message within a RADIUS Access-Accept or Access-Reject Howlett & Hartman Expires May 3, 2012 [Page 5] Internet-Draft SAML RADIUS October 2011 message. The SAML responder MUST NOT include more than one SAML response. A SAML responder that refuses to perform a message exchange with the SAML requester MUST silently discard the SAML request. A SAML responder MAY also return an unsolicited responser (a SAML response generated and emitted in the absence of a request from a SAML requester). This binding is intended to be composed with any use of RADIUS, such as network access. Therefore, other arbitrary RADIUS attributes MAY be used in either the request of response. In the case of a SAML processing error and successful authentication, the RADIUS server SHOULD include a SAML-specified 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 element in the SAML response that is transported within the Access-Reject packet sent by the RADIUS server. 4.2.1. Metadata Considerations There are no metadata considerations particular to this binding. 5. 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 use the GSS EAP mechanism to authenticate the Principal. The Relying Party, acting as an EAP pass-through authenticator, acts as a conduit for the EAP frames emitted by the User Agent and an EAP server which acts as 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. 5.1. Required Information Identification: TBD Contact information: TBD SAML Confirmation Method Identifiers: The SAML V2.0 "sender vouches" Howlett & Hartman Expires May 3, 2012 [Page 6] Internet-Draft SAML RADIUS October 2011 confirmation method identifier, urn:oasis:names:tc:SAML:2.0:cm:sender-vouches, is used by this profile. Updates: None. 5.2. 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 4 and the GSS EAP mechanism [I-D.ietf-abfab-gss-eap]. This profile is based on the SAML Web Browser Single Sign-On Profile [OASIS.saml-profiles-2.0-os]. There are some important differences between these profiles; specifically: o Authentication. This profile specifically calls out the use of a particular authentication framework (although not a particular authentication mechanism). This is necessary so that the profile is able to build on the AAA and GSS frameworks. o Bindings. This profile does not use any HTTP-based bindings; instead, all SAML protocol messages are transported using the SAML RADIUS binding defined in Section 4. This is intended to minimize the number of bindings that interoperable implementations must support. o Signatures. This profile prohibits the use of digital signatures in SAML elements. This includes signatures in the , and elements. Message source authentication and integrity are provided by the binding's transport. This is intended to simplify the trust model and reduce the size of the SAML payloads. o Requests. The profile does not permit the Relying Party to name the of the . This is intended to simplify the business logic of interoperable implementations. o 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 disgression of the Identity Provider. This is intended to simplify the business logic of interoperable implementations. Howlett & Hartman Expires May 3, 2012 [Page 7] Internet-Draft SAML RADIUS October 2011 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 5.3.1): 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 GSS EAP authentication of the Principal. 2. Relying Party Issues to Identity Provider (Section 5.3.2). In step 2, the Relying Party issues a message to be delivered to the Identity Provider using the SAML RADIUS binding. 3. Identity Provider Identifies Principal (Section 5.3.3). In step 3, the Principal is identified by the Identity Provider using EAP authentication, while honoring any requirements imposed by the Relying Party in the message. 4. Identity Provider Issues to Relying Party (Section 5.3.4). In step 4, the Identity Provider issues a 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. Howlett & Hartman Expires May 3, 2012 [Page 8] Internet-Draft SAML RADIUS October 2011 5. Relying Party Grants or Denies Access to Principal (Section 5.3.5). 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. Note that an Identity Provider can initiate this profile at step 4 and issue a message to a Relying Party without the preceding steps. 5.3. 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. If the profile is initiated by the Relying Party, start with Section 5.3.1. If initiated by the Identity Provider, start with Section 5.3.4. 5.3.1. 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 GSS acceptor, MUST invoke the GSS EAP mechanism (either spontaneously or as the result of a mechanism negotiation) and send an EAP-Identity/Request message to the User Agent, acting as a GSS initiator. 5.3.2. Relying Party Issues to Identity Provider The Relying Party, on receiving the EAP-Response/Identity message from the User Agent, MUST send it towards the Identity Provider using the SAML RADIUS binding. The Relying Party MAY include a within this RADIUS Access-Request message. The next hop destination MAY be the Identity Provider or alternatively an intermediate RADIUS proxy. Profile-specific rules for the contents of the element are given in Section 5.4.1. 5.3.3. Identity Provider Identifies Principal The Identity Provider MUST establish the identity of the Principal using EAP authentication, or else it will return an error. If the Howlett & Hartman Expires May 3, 2012 [Page 9] Internet-Draft SAML RADIUS October 2011 ForceAuthn attribute on the element 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 EAP method to authenticate the Principal, subject to the requirements of Section 5.8 of [I-D.ietf-abfab-gss-eap]. and any others called out in the message. 5.3.4. Identity Provider Issues to Relying Party Regardless of the success or failure of the , the Identity Provider MUST produce a message to be delivered to the Relying Party using the SAML RADIUS binding. Profile-specific rules regarding the contents of the element are given in Section 5.4.2. 5.3.5. Relying Party Grants or Denies Access to Principal The Relying Party MUST process the message and any enclosed elements as described in [OASIS.saml-core-2.0-os]. Any subsequent use of the 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. To complete the profile, the Relying Party creates a GSS security context for the User Agent. 5.4. 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. 5.4.1. Usage 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 Identity Provider cannot or will not satisfy the request, it MUST respond with a message containing an Howlett & Hartman Expires May 3, 2012 [Page 10] Internet-Draft SAML RADIUS October 2011 appropriate error status code or codes. If the Relying Provider wishes to permit the Identity Provider to establish a new identifier for the principal if none exists, it MUST include a 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 Relying Party MUST NOT include a element in the request. The authenticated EAP Identity implicitly names the Principal of the requested to the Identity Provider. The message MUST NOT be signed. Authentication and integrity are provided by the RADIUS SAML binding. 5.4.2. Usage If the Identity Provider wishes to return an error, it MUST NOT include any assertions in the . Otherwise, if the request is successful (or if the response is not associated with a request), the element MUST conform to the following: o It MUST NOT be signed. o It MUST contain exactly one . The element of this assertion MUST refer to the authenticated Principal. o The assertion MUST contain a . This MUST contain a element with at least one 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 , then the InResponseTo attribute MUST match the request's ID. o Other statements and confirmation methods MAY be included in the assertion at the discretion of the Identity Provider. In particular, elements MAY be included. Deployers should be aware of the implications of allowing weaker confirmation as the processing as defined in section 2.4.1.1 of [OASIS.saml-core-2.0-os] is effectively satisfy-any. o Other conditions MAY be included as requested by the Relying Party or at the discretion of the Identity Provider. The Identity Howlett & Hartman Expires May 3, 2012 [Page 11] Internet-Draft SAML RADIUS October 2011 Provider is NOT obligated to honor the requested set of in the , if any. 5.4.3. samlp:Response Message Processing Rules The Relying Party MUST do the following: o Verify that the InResponseTo attribute in the bearer equals the ID of its original message, unless the response is unsolicited, in which case the attribute MUST NOT be present. o If a used to establish a security context for the Principal contains a SessionNotOnOrAfter attribute, the 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. 5.4.4. Unsolicited Responses An Identity Provider MAY initiate this profile by delivering an unsolicited message to a Relying Party. An unsolicited MUST NOT contain an InResponseTo attribute, nor should any sender-vouches elements contain one. 5.4.5. Use of the SAML RADIUS Binding It is RECOMMENDED that the RADIUS exchange is protected using TLS encryption for RADIUS [I-D.ietf-radext-radsec] to provide confidentiality and improve integrity protection. 5.4.6. Metadata Considerations There are no metadata considerations particular to this binding. 6. Abfab Assertion Query/Request Profile Howlett & Hartman Expires May 3, 2012 [Page 12] Internet-Draft SAML RADIUS October 2011 7. Security Considerations TODO 8. IANA Considerations Assignments of additional enumerated values for the RADIUS attributes defined in this document are to be processed as described in [RFC3575], subject to the additional requirements of a published specification. 9. References 9.1. 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. [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. [RFC3575] Aboba, B., "IANA Considerations for RADIUS (Remote Authentication Dial In User Service)", RFC 3575, July 2003. [RFC4282] Aboba, B., Beadles, M., Arkko, J., and P. Eronen, "The Network Access Identifier", RFC 4282, December 2005. [I-D.ietf-radext-radsec] Winter, S., McCauley, M., Venaas, S., and K. Wierenga, "TLS encryption for RADIUS", draft-ietf-radext-radsec-09 (work in progress), July 2011. [I-D.ietf-abfab-gss-eap] Hartman, S. and J. Howlett, "A GSS-API Mechanism for the Extensible Authentication Protocol", draft-ietf-abfab-gss-eap-04 (work in progress), October 2011. Howlett & Hartman Expires May 3, 2012 [Page 13] Internet-Draft SAML RADIUS October 2011 9.2. Informative References [RFC3588] Calhoun, P., Loughney, J., Guttman, E., Zorn, G., and J. Arkko, "Diameter Base Protocol", RFC 3588, September 2003. [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-02 (work in progress), March 2011. [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-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. Authors' Addresses Josh Howlett JANET(UK) 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 Howlett & Hartman Expires May 3, 2012 [Page 14]