Name Attributes for the GSS-API EAP mechanism
draft-ietf-abfab-gss-eap-naming-04

Network Working Group                                         S. Hartman
Internet-Draft                                         Painless Security
Intended status: Standards Track                              J. Howlett
Expires: February 15, 2013                                     JANET(UK)
                                                         August 14, 2012

             Name Attributes for the GSS-API EAP mechanism
                   draft-ietf-abfab-gss-eap-naming-04

Abstract

   The naming extensions to the Generic Security Services Application
   Programming interface provide a mechanism for applications to
   discover authorization and personalization information associated
   with GSS-API names.  The Extensible Authentication Protocol GSS-API
   mechanism allows an Authentication/Authorization/Accounting peer to
   provide authorization attributes along side an authentication
   response.  It also provides mechanisms to process Security Assertion
   Markup Language (SAML) messages provided in the AAA response.  This
   document describes the necessary information to use the naming
   extensions API to access that information.

Status of this Memo

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   (http://trustee.ietf.org/license-info) in effect on the date of

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   publication of this document.  Please review these documents
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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Requirements notation  . . . . . . . . . . . . . . . . . . . .  4
   3.  Naming Extensions and SAML . . . . . . . . . . . . . . . . . .  5
   4.  Federated Context  . . . . . . . . . . . . . . . . . . . . . .  6
   5.  Name Attributes for GSS-EAP  . . . . . . . . . . . . . . . . .  7
   6.  Names of SAML Attributes in the Federated Context  . . . . . .  8
     6.1.  Assertions . . . . . . . . . . . . . . . . . . . . . . . .  8
     6.2.  SAML Attributes  . . . . . . . . . . . . . . . . . . . . .  8
     6.3.  SAML Name Identifiers  . . . . . . . . . . . . . . . . . .  8
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 10
   8.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 11
     8.1.  Registration of the GSS URN Namespace  . . . . . . . . . . 11
   9.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 12
   10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 13
     10.1. Normative References . . . . . . . . . . . . . . . . . . . 13
     10.2. Informative References . . . . . . . . . . . . . . . . . . 13
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 15

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1.  Introduction

   The naming extensions [I-D.ietf-kitten-gssapi-naming-exts]to the
   Generic Security Services Application Programming interface (GSS-API)
   [RFC2743] provide a mechanism for applications to discover
   authorization and personalization information associated with GSS-API
   names.  The Extensible Authentication Protocol GSS-API mechanism
   [I-D.ietf-abfab-gss-eap] allows an Authentication/Authorization/
   Accounting peer to provide authorization attributes along side an
   authentication response.  It also provides mechanisms to process
   Security Assertion Markup Language (SAML) messages provided in the
   AAA response.  Other mechanisms such as SAML EC
   [I-D.ietf-kitten-sasl-saml-ec] also support SAML assertions and
   attributes carried in the GSS-API.  This document describes the
   necessary information to use the naming extensions API to access SAML
   assertions in the federated context and AAA attributes.

   The semantics of setting attributes defined in this specification are
   undefined and left to future work.

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2.  Requirements notation

   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 [RFC2119].

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3.  Naming Extensions and SAML

   SAML assertions can carry attributes describing properties of the
   subject of the assertion.  For example, an assertion might carry an
   attribute describing the organizational affiliation or e-mail address
   of a subject.  According to Section 8.2 and 2.7.3.1 of
   [OASIS.saml-core-2.0-os], the name of an attribute has two parts.
   The first is a URI describing the format of the name.  The second
   part, whose form depends on the format URI, is the actual name.  GSS-
   API name attributes may take a form starting with a URI describing
   the form of the name; the rest of the name is specified by that URI.

   SAML attributes carried in GSS-API names are named with three parts.
   The first is a URN indicating that the name is a SAML attribute and
   describing the context (Section 4).  This URN is followed by a space,
   the URI indicating the format of the SAML name, a space and the SAML
   attribute name.  The URI indicating the format of the SAML attribute
   name is not optional and MUST be present.

   SAML attribute names may not be globally unique.  Many names that are
   named by URNs or URIs are likely to have semantics independent of the
   issuer.  However other name formats, including unspecified name
   formats, make it easy for two issuers to choose the same name for
   attributes with different semantics.  Attributes using the federated
   context Section 4 are issued by the same party performing the
   authentication.  So, based on who is the subject of the name, the
   semantics of the attribute can be determined.

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4.  Federated Context

   GSS-API naming extensions have the concept of an authenticated name
   attribute.  The mechanism guarantees that the contents of an
   authenticated name attribute are an authenticated statement from the
   trusted source of the peer credential.  The fact that an attribute is
   authenticated does not imply that the trusted source of the peer
   credential is authorized to assert the attribute.

   In the federated context, the trusted source of the peer credential
   is typically some identity provider.  In the GSS EAP mechanism,
   information is combined from AAA and SAML sources.  The SAML IDP and
   home AAA server are assumed to be in the same trust domain.  However,
   this trust domain is not typically the same as the trust domain of
   the service.  With other SAML mechanisms using this specification,
   the SAML assertion also comes from the party performing
   authentication.  Typically, the IDP is run by another organization in
   the same federation.  The IDP is trusted to make some statements,
   particularly related to the context of a federation.  For example, an
   academic federation's participants would typically trust an IDP's
   assertions about whether someone was a student or a professor.
   However that same IDP would not typically be trusted to make
   assertions about local entitlements such as group membership.  Thus,
   a service MUST make a policy decision about whether the IDP is
   permitted to assert a particular attribute and about whether the
   asserted value is acceptable.

   In contrast, attributes in an enterprise context are often verified
   by a central authentication infrastructure that is trusted to assert
   most or all attributes.  For example, in a Kerberos infrastructure,
   the KDC typically indicates group membership information for clients
   to a server using KDC-authenticated authorization data.

   The context of an attribute is an important property of that
   attribute; trust context is an important part of this overall
   context.  In order for applications to distinguish the context of
   attributes, attributes with different context need different names.
   This specification defines attribute names for SAML and AAA
   attributes in the federated context.

   These names MUST NOT be used for attributes issued by a party other
   than one closely associated with the source of credentials unless the
   source of credentials is re-asserting the attributes.  For example, a
   source of credentials can consult whatever sources of attributes it
   chooses, but acceptors can assume attributes in the federated context
   are from the source of credentials.

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5.  Name Attributes for GSS-EAP

   This section describes how RADIUS attributes received in an access-
   accept message by the GSS-EAP [I-D.ietf-abfab-gss-eap] mechanism are
   named.  The use of attributes defined in this section for other
   RADIUS messages or prior to the access-accept message is undefined at
   this time.  Future specifations can explore these areas giving
   adequate weight to backward compatibility.

   The first portion of the name is urn:ietf:params:gss:radius-attribute
   (a URN indicating that this is a GSS-EAP RADIUS AVP).  This is
   followed by a space and a numeric RADIUS name as described by section
   2.6 of [I-D.ietf-radext-radius-extensions].  For example the name of
   the User-Name attribute is "urn:ietf:gss:radius-attribute 1".  The
   name of extended type 1 within type 241 would be
   "urn:ietf:gss:radius-attribute 241.1".

   The value of RADIUS attributes is the raw octets of the packet.
   Integers are in network byte order.  The display value SHOULD be a
   human readable string; an implementation can only produce this string
   if it knows the type of a given RADIUS attribute.  If multiple
   attributes are present with a given name in the RADIUS message, then
   a multi-valued GSS-API attribute SHOULD be returned.  As an
   exception, implementations SHOULD concatenate RADIUS attributes such
   as EAP-Message or large attributes defined in
   [I-D.ietf-radext-radius-extensions] that use multiple attributes to
   carry more than 253 octets of information.

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6.  Names of SAML Attributes in the Federated Context

6.1.  Assertions

   An assertion generated by the credential source is named by
   "urn:ietf:params:gss:federated-saml-assertion".  The value of this
   attribute is the assertion carried in the AAA protocol or used for
   authentication in a SAML mechanism.  This attribute is absent from a
   given acceptor name if no such assertion is present or if the
   assertion fails local policy checks.  This attribute is always
   authenticated when present in mechanism names for mechanisms
   complying with this specification: authentication only succeeds if
   the SAML or AAA exchange is successfully authenticated.  However,
   users of the GSS-API MUST confirm that the attribute is authenticated
   because some other mechanisms MAY permit an initiator to assert an
   unauthenticated version of this attribute.

6.2.  SAML Attributes

   Each attribute carried in the assertion SHOULD also be a GSS name
   attribute.  The name of this attribute has three parts, all separated
   by an ASCII space character.  The first part is
   urn:ietf:params:gss:federated-saml-attribute.  The second part is the
   URI for the <saml:Attribute> element's NameFormat XML attribute.  The
   final part is the <saml:Attribute> element's Name XML attribute.

   If the content of each <saml:AttributeValue> element is a simple text
   node (or nodes), then the raw and "display" values of the GSS name
   attribute MUST be the text content of the element(s).  The raw value
   MUST be encoded as UTF-8.

   If the value is not simple or is empty, then the raw value(s) of the
   GSS name attribute MUST be the well-formed serialization of the
   <saml:AttributeValue> element(s) encoded as UTF-8.  The "display"
   values are implementation-defined.

   These attributes SHOULD be marked authenticated if they are contained
   in SAML assertions that have been successfully validated back to the
   trusted source of the peer credential.  In the GSS-EAP mechanism, a
   SAML assertion carried in an integrity-protected and authenticated
   AAA protocol SHALL be sufficiently validated.  An implementation MAY
   apply local policy checks to this assertion and discard it if it is
   unacceptable according to these checks.

6.3.  SAML Name Identifiers

   The <saml:NameID> carried in the subject of the assertion SHOULD also
   be a GSS name attribute.  The name of this attribute has two parts,

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   separated by an ASCII space character.  The first part is
   urn:ietf:params:gss:federated-saml-nameid.  The second part is the
   URI for the <saml:NameID> element's Format XML attribute.

   The raw value of the GSS name attribute MUST be the well-formed
   serialization of the <saml:NameID> element encoded as UTF-8.  The
   "display" value is implementation-defined.  For formats defined by
   section 8.3 of [OASIS.saml-core-2.0-os], missing values of the
   NameQualifier or SPNameQualifier XML attributes MUST be populated in
   accordance with the definition of the format prior to serialization.
   In other words, the defaulting rules specified for the "persistent"
   and "transient" formats MUST be applied prior to serialization.

   This attribute SHOULD be marked authenticated if the name identifier
   is contained in a SAML assertion that has been successfully validated
   back to the trusted source of the peer credential.  In the GSS-EAP
   mechanism, a SAML assertion carried in an integrity-protected and
   authenticated AAA protocol SHALL be sufficiently validated.  An
   implementation MAY apply local policy checks to this assertion and
   discard it if it is unacceptable according to these checks.

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7.  Security Considerations

   This document describes how to access RADIUS attributes, SAML
   attributes and SAML assertions from some GSS-API mechanisms.  These
   attributes are typically used for one of two purposes.  The least
   sensitive is personalization: a central service MAY provide
   information about an authenticated user so they need not enter it
   with each acceptor they access.  A more sensitive use is
   authorization.

   The mechanism is responsible for authentication and integrity
   protection of the attributes.  However, the acceptor application is
   responsible for making a decision about whether the credential source
   is trusted to assert the attribute and validating the asserted value.

   mechanisms are permitted to perform local policy checks on SAML
   assertions, attributes and name identifiers exposed through name
   attributes defined in this document.  If there is another way to get
   access to the SAML assertion, for example the mechanism described in
   [I-D.ietf-abfab-aaa-saml], then an application MAY get different
   results depending on how the SAML is accessed.  This is intended
   behavior; applications who choose to bypass local policy checks
   SHOULD perform their own evaluation before relying on information.

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8.  IANA Considerations

   A new top-level registry is created titled "Generic Security Service
   Application Program Interface Parameters".  There doesn't seem to be
   an existing top-level registry that can be used.  There are
   Parameters for the Kerberos V mechanism; parameters for the GSS-API
   EAP mechanism; and GSS-API/SASL/Kerberos service names.  However none
   of these are the right place.

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

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

                +--------------------------+-------------+
                | Parameter                | Reference   |
                +--------------------------+-------------+
                | radius-attribute         | Section 5   |
                |                          |             |
                | federated-saml-assertion | Section 6.1 |
                |                          |             |
                | federated-saml-attribute | Section 6.2 |
                |                          |             |
                | federated-saml-nameid    | Section 6.3 |
                +--------------------------+-------------+

8.1.  Registration of the GSS URN Namespace

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

   Registry Name: gss

   Specification: draft-ietf-abfab-gss-eap-naming

   Repository: GSS-API URN Parameters (Section 8)

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

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9.  Acknowledgements

   Scott Cantor contributed significant text and multiple reviews of
   this document.

   Sam hartman's work on this specification has been funded by Janet.

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10.  References

10.1.  Normative References

   [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-09 (work in progress),
              August 2012.

   [I-D.ietf-kitten-gssapi-naming-exts]
              Williams, N., Johansson, L., Hartman, S., and S.
              Josefsson, "GSS-API Naming Extensions",
              draft-ietf-kitten-gssapi-naming-exts-15 (work in
              progress), May 2012.

   [I-D.ietf-radext-radius-extensions]
              DeKok, A. and A. Lior, "Remote Authentication Dial In User
              Service (RADIUS) Protocol Extensions",
              draft-ietf-radext-radius-extensions-06 (work in progress),
              June 2012.

   [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.

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

   [RFC2743]  Linn, J., "Generic Security Service Application Program
              Interface Version 2, Update 1", RFC 2743, January 2000.

   [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.

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

10.2.  Informative References

   [I-D.ietf-abfab-aaa-saml]
              Howlett, J. and S. Hartman, "A RADIUS Attribute, Binding
              and Profiles for SAML", draft-ietf-abfab-aaa-saml-03 (work
              in progress), March 2012.

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   [I-D.ietf-kitten-sasl-saml-ec]
              Cantor, S. and S. Josefsson, "SAML Enhanced Client SASL
              and GSS-API Mechanisms", draft-ietf-kitten-sasl-saml-ec-02
              (work in progress), August 2012.

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Authors' Addresses

   Sam Hartman
   Painless Security

   Email: hartmans-ietf@mit.edu

   Josh Howlett
   JANET(UK)

   Email: josh.howlett@ja.net

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