Network Working Group S. Hartman
Internet-Draft Painless Security
Intended status: Standards Track J. Howlett
Expires: April 16, 2011 JANET(UK)
October 13, 2010
Name Attributes for the GSS-API EAP mechanism
draft-ietf-abfab-gss-eap-naming-00
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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This Internet-Draft will expire on April 16, 2011.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Requirements notation . . . . . . . . . . . . . . . . . . . . 4
3. Naming Extensions and SAML . . . . . . . . . . . . . . . . . . 5
4. RADIUS and Authenticated Attributes . . . . . . . . . . . . . 6
5. Name Attributes for GSS-EAP . . . . . . . . . . . . . . . . . 8
5.1. Assertions . . . . . . . . . . . . . . . . . . . . . . . . 8
5.2. SAML Attributes . . . . . . . . . . . . . . . . . . . . . 8
5.3. RADIUS Attributes . . . . . . . . . . . . . . . . . . . . 8
6. Security Considerations . . . . . . . . . . . . . . . . . . . 9
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
8. Normative References . . . . . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 12
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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.howlett-eap-gss] 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.
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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 [SAMLCORE],
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. As of June 2010, GSS-
API name attributes take the form of a single URI.
Administrators may need to type SAML attribute names into
configuration files or otherwise tell applications how to find
attributes. It is desirable to support accessing these attributes
from applications that have no awareness of SAML. So, the GSS-API
attribute name should be something that an administrator can
reasonably easily construct from a SAML attribute name. In
particular, adding or removing URI escapes, base64 encoding or
similar transformations would significantly decrease usability.
Instead, it seems desirable to extend GSS-API naming extensions to
support concepts such as SAML names where the format is specified
separately. The format of GSS-API attribute names should be changed.
If no space character is found in the name, then the name is
interpreted as a URI describing the attribute. Otherwise, the
portion from the beginning of the buffer to the first space is
interpreted as a URI describing the form and interpretation of the
rest of the buffer; this portion is known as the attribute type URI.
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4. RADIUS and Authenticated Attributes
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. 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 the context.
Applications will often want to treat an attribute in a federated
context the same as an attribute in an enterprise context. In order
for applications to distinguish the context of attributes, attributes
with different context need different names. For example, the name
of an attribute containing the initiator's e-mail address in a
federated context needs to be different from the name containing the
initiator's e-mail address in a different context. The determination
of trust from this context information can never be exact: Kerberos
typically is used in environments where the KDC is fairly trusted,
but an application could have a key in a realm that it does not fully
trust. Similarly, SAML is typically in a federated context, but an
organization could use SAML for internal authentication as well.
It would be convenient to use the same GSS-API attribute names for
the same information regardless of context. However, when
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considering attribute names it is critical to consider the
appropriate interpretation of that name and the distinctions an
application will need to make about the name. As a result, it is
often the case that attributes from two different mechanisms will
have different names.
However, the local implementation of the mechanism and layers in the
GSS-API implementation above the mechanism can make the job of the
application easier. If local policy permits an attribute to be
trusted, then the attribute can be copied to a name whose context
indicates that local policy has been applied. For example, an
implementation could have an attribute for e-mail address that
received the value both of a SAML mechanism and Kerberos mechanism's
e-mail address attributes after local policy is applied. Such
mechanism-level attributes can also be used to normalize the format
of attribute values.
In the case of GSS-EAP, the attribute names need to be specific to
SAML attributes obtained via AAA transport.
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5. Name Attributes for GSS-EAP
This section describes how SAML assertions, SAML attributes and
RADIUS attributes received with the GSS-EAP mechanism are named.
5.1. Assertions
Implementations of GSS-EAP MUST support an attribute with the name
"urn:ietf:params:gss-eap:saml-aaa-assertion". The value of this
attribute is the assertion carried in the AAA protocol. 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 authentic when present: authentication only
succeeds if the AAA exchange is successfully authenticated. However,
users of the GSS-API MUST confirm that the attribute is authenticated
because some mechanisms MAY permit an initiator to assert an
unauthenticated version of this attribute.
5.2. 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-eap:saml-attr. The second part is the URI for
the SAML attribute name format. The final part is the name of the
SAML attribute. If the mechanism performs an additional attribute
query, the retrieved attributes SHOULD be GSS-API name attributes
using the same name syntax.
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.
Attribute query results made based on this assertion also count as
originating with the source of the peer credential. The
implementation MUST validate the authenticity of these results before
they are processed.
5.3. RADIUS Attributes
A mechanism needs to be created to give applications access to AAA
AVPs carried along with an access-accept message.
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6. Security Considerations
This needs to be written.
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7. IANA Considerations
This section needs to include URN registrations within the IETF
namespace for URNs that are used.
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8. Normative References
[I-D.howlett-eap-gss]
Hartman, S. and J. Howlett, "A GSS-API Mechanism for the
Extensible Authentication Protocol",
draft-howlett-eap-gss-00 (work in progress), March 2010.
[I-D.ietf-kitten-gssapi-naming-exts]
Williams, N. and L. Johansson, "GSS-API Naming
Extensions", draft-ietf-kitten-gssapi-naming-exts-08 (work
in progress), June 2010.
[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.
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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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