Network Working Group S. Hartman
Internet-Draft Painless Security
Intended status: Standards Track J. Howlett
Expires: September 13, 2012 JANET(UK)
March 12, 2012
Name Attributes for the GSS-API EAP mechanism
draft-ietf-abfab-gss-eap-naming-02
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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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
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 12
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 13
10.1. Normative References . . . . . . . . . . . . . . . . . . . 13
10.2. Informative References . . . . . . . . . . . . . . . . . . 13
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 14
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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.
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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. 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 URI 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 with the GSS-
EAP mechanism are named.
The first portion of the name is urn:ietf:params:gss:radius-attr (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-attr 1". The name of
extended type 1 within type 241 would be "urn:ietf:gss:radius-attr
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.
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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:fed-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
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.
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:fed-saml-attr. 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, 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,
separated by an ASCII space character. The first part is
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urn:ietf:params:gss:fed-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 [SAMLCORE], 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.
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8. IANA Considerations
First, a new registry needs to be created for GSS URNs. Then, this
needs to be registered in the IETF's URN registry. Then this
registry needs to be populated with URN items from this spec.
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9. Acknowledgements
Scott Cantor contributed significant text and multiple reviews of
this document.
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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-05 (work in progress),
March 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-13 (work in
progress), March 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-04 (work in progress),
January 2012.
[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.
10.2. Informative References
[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-01
(work in progress), February 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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