Internet DRAFT - draft-ietf-abfab-gss-eap-naming
draft-ietf-abfab-gss-eap-naming
Network Working Group S. Hartman
Internet-Draft Painless Security
Intended status: Standards Track J. Howlett
Expires: May 18, 2013 JANET(UK)
November 14, 2012
Name Attributes for the GSS-API EAP mechanism
draft-ietf-abfab-gss-eap-naming-07
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
This Internet-Draft is submitted in full conformance with the
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This Internet-Draft will expire on May 18, 2013.
Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
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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 . . . . . . . . . . . . . . . . . 8
6. Names of SAML Attributes in the Federated Context . . . . . . 9
6.1. Assertions . . . . . . . . . . . . . . . . . . . . . . . . 9
6.2. SAML Attributes . . . . . . . . . . . . . . . . . . . . . 9
6.3. SAML Name Identifiers . . . . . . . . . . . . . . . . . . 10
7. Security Considerations . . . . . . . . . . . . . . . . . . . 11
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
8.1. Registration of the GSS URN Namespace . . . . . . . . . . 12
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 14
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 15
10.1. Normative References . . . . . . . . . . . . . . . . . . . 15
10.2. Informative References . . . . . . . . . . . . . . . . . . 16
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 17
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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 (AAA) 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 Universal Resource Identifier (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 Universal Resource Name (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. This policy can be implemented as
local configuration on the service, as rules in AAA proxies, or
through other deployment-specific mechanisms.
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. This requirement is typically
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enforced in mechanism specifications. For example
[I-D.ietf-abfab-aaa-saml] provides enough information thatwe know the
attributes it carries today are in the federated context. Similarly,
we know that the requirements of this paragraph are met by SAML
mechanisms where the assertion is the means of authentication.
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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. In particular, this
specification defines the meaning of these attributes for the
src_name output of GSS_Accept_sec_context after that function returns
GSS_S_COMPLETE. Attributes MAY be absent or values MAY change in
other circumstances; future specifications MAY define this behavior.
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:params:gss:radius-attribute 1".
The name of extended type 1 within type 241 would be
"urn:ietf:params:gss:radius-attribute 241.1".
Consider a case where the RADIUS access-accept response includes the
RADIUS username attribute. An application wishing to retrieve the
value of this attribute would first wait until GSS-
_Accept_sec_Context returned GSS_S_COMPLETE. Then the application
would take the src_name output from GSS_Accept_sec_context and call
GSS_Get_name_attribute passing this name and an attribute of
"urn:ietf:params:gss:radius-attribute 1" as inputs. After confirming
that the authenticated boolean output is true, the application can
find the username in the values output.
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.
When GSS_Get_name_attribute is called, This attribute will be
returned with the authenticated output set to true only if the
mechanism can successfully authenticate the SAML statement. For the
GSS-EAP mechanism this is true if the AAA exchange has successfully
authenticated. However, uses of the GSS-API MUST confirm that the
attribute is marked authenticated as other mechanisms MAY permit an
initiator to provide an unauthenticated SAML statement.
Mechanisms MAY perform additional local policy checks and MAY remove
the attribute corresponding to assertions that fail these checks.
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. The
SAML attribute name may itself contain spaces. As required by the
URI specification, spaces within a URI are encoded as "%20". Spaces
within a URI, including either the first or second part of the name,
encoded as "%20" do not separate parts of the GSS-API attribute name;
they are simply part of the URI.
As an example, if the eduPersonEntitlement attribute is present in an
assertion, then an attribute with the name
"urn:ietf:params:gss:federated-saml-attribute
urn:oasis:names:tc:SAML:2.0:attrname-format:uri
urn:oid:1.3.6.1.4.1.5923.1.1.1.7" could be returned from
GSS_Inquire_Name. If an application calls GSS_Get_name_attribute
with this attribute in the attr parameter then the values output
would include one or more URIs of entitlements that were associated
with the authenticated user.
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
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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 a namespace well-formed serialization
[XMLNS]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 successfully validated; attributes from that
assertion SHALL be returned from GSS_Get_name_attribute with the
authenticated output set to true. An implementation MAY apply local
policy checks to each attribute in this assertion and discard the
attribute 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,
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".
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].
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: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
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URI encoding where necessary.
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9. Acknowledgements
Scott Cantor contributed significant text and multiple reviews of
this document.
The authors would like to thank Stephen Farrell, Luke Howard, and Jim
Schaad
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.
[XMLNS] W3C, "XML Namespaces Conformance", 2009, <http://
www.w3.org/TR/2009/REC-xml-names-20091208/#Conformance>.
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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-04 (work
in progress), October 2012.
[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-04
(work in progress), October 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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