A RADIUS Attribute, Binding, Profiles, Name Identifier Format, and Confirmation Methods for SAML
draft-ietf-abfab-aaa-saml-11
The information below is for an old version of the document.
| Document | Type |
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|---|---|---|---|
| Authors | Josh Howlett , Sam Hartman , Alejandro Pérez-Méndez | ||
| Last updated | 2015-10-05 (Latest revision 2015-08-07) | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
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draft-ietf-abfab-aaa-saml-11
ABFAB J. Howlett
Internet-Draft Janet
Intended status: Informational S. Hartman
Expires: February 8, 2016 Painless Security
A. Perez-Mendez, Ed.
University of Murcia
August 7, 2015
A RADIUS Attribute, Binding, Profiles, Name Identifier Format, and
Confirmation Methods for SAML
draft-ietf-abfab-aaa-saml-11
Abstract
This document describes the use of the Security Assertion Mark-up
Language (SAML) with RADIUS in the context of the ABFAB architecture.
It defines two RADIUS attributes, a SAML binding, a SAML name
identifier format, two SAML profiles, and two SAML confirmation
methods. The RADIUS attributes permit encapsulation of SAML
assertions and protocol messages within RADIUS, allowing SAML
entities to communicate using the binding. The two profiles describe
the application of this binding for ABFAB authentication and
assertion query/request, enabling a Relying Party to request
authentication of, or assertions for, users or machines (Clients).
These Clients may be named using a NAI name identifier format.
Finally, the subject confirmation methods allow requests and queries
to be issued for a previously authenticated user or machine without
needing to explicitly identify them as the subject. These artifacts
have been defined to permit application in AAA scenarios other than
ABFAB, 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 February 8, 2016.
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Copyright Notice
Copyright (c) 2015 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
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
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. RADIUS SAML Attributes . . . . . . . . . . . . . . . . . . . 5
3.1. SAML-Assertion attribute . . . . . . . . . . . . . . . . 5
3.2. SAML-Message attribute . . . . . . . . . . . . . . . . . 6
4. SAML RADIUS Binding . . . . . . . . . . . . . . . . . . . . . 7
4.1. Required Information . . . . . . . . . . . . . . . . . . 7
4.2. Operation . . . . . . . . . . . . . . . . . . . . . . . . 7
4.3. Processing of names . . . . . . . . . . . . . . . . . . . 9
4.3.1. AAA names . . . . . . . . . . . . . . . . . . . . . . 9
4.3.2. SAML names . . . . . . . . . . . . . . . . . . . . . 9
4.3.3. Mapping of AAA names in SAML metadata . . . . . . . . 10
4.3.4. Example of SAML metadata including AAA names . . . . 12
4.4. Use of XML Signatures . . . . . . . . . . . . . . . . . . 13
4.5. Metadata Considerations . . . . . . . . . . . . . . . . . 13
5. Network Access Identifier Name Identifier Format . . . . . . 13
6. RADIUS State Confirmation Method Identifiers . . . . . . . . 13
7. ABFAB Authentication Profile . . . . . . . . . . . . . . . . 14
7.1. Required Information . . . . . . . . . . . . . . . . . . 14
7.2. Profile Overview . . . . . . . . . . . . . . . . . . . . 14
7.3. Profile Description . . . . . . . . . . . . . . . . . . . 16
7.3.1. Client Request to Relying Party . . . . . . . . . . . 16
7.3.2. Relying Party Issues <samlp:AuthnRequest> to Identity
Provider . . . . . . . . . . . . . . . . . . . . . . 16
7.3.3. Identity Provider Identifies Client . . . . . . . . . 17
7.3.4. Identity Provider Issues <samlp:Response> to Relying
Party . . . . . . . . . . . . . . . . . . . . . . . . 17
7.3.5. Relying Party Grants or Denies Access to Client . . . 17
7.4. Use of Authentication Request Protocol . . . . . . . . . 17
7.4.1. <samlp:AuthnRequest> Usage . . . . . . . . . . . . . 18
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7.4.2. <samlp:Response> Message Usage . . . . . . . . . . . 18
7.4.3. <samlp:Response> Message Processing Rules . . . . . . 19
7.4.4. Unsolicited Responses . . . . . . . . . . . . . . . . 19
7.4.5. Use of the SAML RADIUS Binding . . . . . . . . . . . 19
7.4.6. Use of XML Signatures . . . . . . . . . . . . . . . . 20
7.4.7. Metadata Considerations . . . . . . . . . . . . . . . 20
8. ABFAB Assertion Query/Request Profile . . . . . . . . . . . . 20
8.1. Required Information . . . . . . . . . . . . . . . . . . 20
8.2. Profile Overview . . . . . . . . . . . . . . . . . . . . 20
8.3. Profile Description . . . . . . . . . . . . . . . . . . . 21
8.3.1. Differences from the SAML V2.0 Assertion
Query/Request Profile . . . . . . . . . . . . . . . . 21
8.3.2. Use of the SAML RADIUS Binding . . . . . . . . . . . 22
8.3.3. Use of XML Signatures . . . . . . . . . . . . . . . . 22
8.3.4. Metadata Considerations . . . . . . . . . . . . . . . 22
9. Privacy considerations . . . . . . . . . . . . . . . . . . . 22
10. Security Considerations . . . . . . . . . . . . . . . . . . . 23
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 24
11.1. RADIUS Attributes . . . . . . . . . . . . . . . . . . . 24
11.2. ABFAB Parameters . . . . . . . . . . . . . . . . . . . . 24
11.3. Registration of the ABFAB URN Namespace . . . . . . . . 25
12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 25
13. References . . . . . . . . . . . . . . . . . . . . . . . . . 25
13.1. Normative References . . . . . . . . . . . . . . . . . . 25
13.2. Informative References . . . . . . . . . . . . . . . . . 27
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 28
1. Introduction
Within the ABFAB architecture [I-D.ietf-abfab-arch] it is often
desirable to convey Security Assertion Mark-up Language (SAML)
assertions and protocol messages.
SAML typically only considers the use of HTTP-based transports, known
as bindings [OASIS.saml-bindings-2.0-os], which are primarily
intended for use with the SAML V2.0 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 applications by building on the AAA framework. Consequently
there exists a requirement for SAML to integrate with the AAA
framework and protocols such as RADIUS [RFC2865] and Diameter
[RFC3588], in addition to HTTP.
In summary this document specifies:
o Two RADIUS attributes to encapsulate SAML assertions and protocol
messages respectively.
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o A SAML RADIUS binding that defines how SAML assertions and
protocol messages can be transported by RADIUS within a SAML
exchange.
o A SAML name identifier format in the form of a Network Access
Identifier.
o A profile of the SAML Authentication Request Protocol that uses
the SAML RADIUS binding to effect SAML-based authentication and
authorization.
o A profile of the SAML Assertion Query And Request Protocol that
uses the SAML RADIUS binding to effect the query and request of
SAML assertions.
o Two SAML Subject Confirmation Methods for indicating that a user
or machine client is the subject of an assertion.
This document adheres to the guidelines stipulated by
[OASIS.saml-bindings-2.0-os] and [OASIS.saml-profiles-2.0-os] for
defining new SAML bindings and profiles respectively, and other
conventions applied formally or otherwise within SAML. In particular
where this document provides a 'Required Information' section for the
binding and profiles that enumerate:
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.
1.1. Terminology
This document uses terminology from a number of related standards,
which tend to addopt different terms for similar or identical
concepts. In general the document uses, when possible, the ABFAB
term for the entity, as described in [I-D.ietf-abfab-arch]. For
reference we include this table which maps the different terms into a
single view.
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+----------+-----------+------------------+-------------------+
| Protocol | Client | Relying Party | Identity Provider |
+----------+-----------+------------------+-------------------+
| ABFAB | Client | Relying Party | Identity Provider |
| | | | |
| SAML | Subject | Service Provider | Identity Provider |
| | Principal | Requester | Responder |
| | | Consumer | Issuer |
| | | | |
| RADIUS | User | NAS | AS |
| | | RADIUS client | RADIUS server |
+----------+-----------+------------------+-------------------+
Table 1. Terminology
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 Attributes
The RADIUS SAML binding defined in Section 4 of this document uses
two attributes to convey SAML assertions and protocol messages
respectively [OASIS.saml-core-2.0-os]. Owing to the typical size of
these structures, these attributes use the Long Extended Type format
[RFC6929] to encapsulate their data.
3.1. SAML-Assertion attribute
This attribute is used to encode a SAML assertion. The following
figure represents the format of this attribute.
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 | Extended-Type |M| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Value...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: SAML-Assertion format
Type
245 (To be confirmed by IANA)
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Length
>= 5
Extended-Type
TBD1
M (More)
As described in [RFC6929].
Reserved
As described in [RFC6929].
Value
One or more octets encoding a SAML assertion.
3.2. SAML-Message attribute
This attribute is used to encode a SAML protocol message. The
following figure represents the format of this attribute.
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 | Extended-Type |M| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Value...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: SAML-Message format
Type
245 (To be confirmed by IANA)
Length
>= 5
Extended-Type
TBD2
M (More)
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As described in [RFC6929].
Reserved
As described in [RFC6929].
Value
One or more octets encoding a SAML protocol message.
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 assertions and
protocol messages.
4.1. Required Information
Identification: urn:ietf:params:abfab:bindings:radius
Contact information: iesg@ietf.org
Updates: None.
4.2. Operation
RADIUS can be used over multiple underlying transports. It is
REQUIRED that the RADIUS exchange is protected using TLS encryption
for RADIUS [RFC6614] to provide confidentiality and improve integrity
protection, unless alternative methods are used to ensure
confidentiality, such as IPSEC tunnels or a sufficiently secure
internal network.
Implementations of this profile can take advantage of mechanisms to
permit the transport of longer SAML messages over RADIUS transports,
such as the Support of fragmentation of RADIUS packets [RFC7499] or
Larger Packets for RADIUS over TCP [I-D.ietf-radext-bigger-packets].
There are two system models for the use of SAML over RADIUS. The
first is a 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 Relying Party (RP), 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
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Identifier [RFC7542] scheme. The Relying Party MUST NOT include
more than one SAML request element.
2. The RADIUS server, acting as an Identity Provider (IdP), returns
a SAML protocol message within a RADIUS Access-Accept or Access-
Reject message. These messages necessarily conclude a RADIUS
exchange and therefore this is the only opportunity for the
Identity Provider to send a response in the context of this
exchange. The Identity Provider MUST NOT include more than one
SAML response. An IdP that refuses to perform a message exchange
with the Relying Party can silently discard the SAML request
(this could subsequently be followed by a RADIUS Access-Reject,
as the same conditions that cause the IdP to discard the SAML
request may also cause the RADIUS server to fail to
authenticate).
The second system model permits a RADIUS server acting as an Identity
Provider to use the RADIUS SAML-Assertion attribute defined in
Section 3 to encapsulate an unsolicited SAML assertion. This
attribute MUST be included in a RADIUS Access-Accept message. When
included, the attribute MUST contain a single SAML assertion.
RADIUS servers MUST NOT include both the SAML-Message and the SAML-
Assertion attribute in the same RADIUS message. If an IdP is
producing a response to a SAML request, then the first system model
is used. An IdP MAY ignore a SAML request and send an unsolicited
assertion using the second system model using the RADIUS SAML-
Assertion attribute.
In either system model, Identity Providers SHOULD return a RADIUS
state attribute as part of the Access-Accept message so that future
SAML queries or requests can be run against the same context of an
authentication exchange.
This binding is intended to be composed with other uses of RADIUS,
such as network access. Therefore, other arbitrary RADIUS attributes
will be used in either the request or response.
In the case of a SAML processing error and successful authentication,
the RADIUS server SHOULD include a SAML-specified <samlp:Status>
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 <samlp:Status> element in
the SAML response that is transported within the Access-Reject packet
sent by the RADIUS server.
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4.3. Processing of names
SAML entities using profiles of this binding will typically possess
both the SAML and AAA names of their correspondents. Frequently
these entities will need to apply policies using these names; for
example, when deciding to release attributes. Often these policies
will be security-sensitive, and so it is important that policy is
applied on these names consistently.
4.3.1. AAA names
These rules relate to the processing of AAA names by SAML entities
using profiles of this binding.
o Identity Providers SHOULD apply policy based on the Relying
Party's identity associated with the RADIUS Access-Request.
o Relying Parties SHOULD apply policy based on the NAI realm
associated with the RADIUS Access-Accept.
4.3.2. SAML names
These rules relate to the processing of SAML names by SAML entities
using profiles of this binding.
Identity Providers MAY apply policy based on the Relying Party's SAML
<entityId>. In such cases, at least one of the following methods is
required in order to establish a relation between the SAML name and
the AAA name of the Relying Party:
o RADIUS client identity in trusted digitally signed SAML request.
o RADIUS client identity in trusted SAML federation metadata (as in
[OASIS.saml-metadata-2.0-os]).
A digitally signed SAML request without the RADIUS client identity is
not sufficient, since a malicious RADIUS entity can observe a SAML
message and include it in a different RADIUS message without the
consent of the issuer of that SAML message. If an Identity Provider
were to process the SAML message without confirming that it applied
to the RADIUS message, inappropriate policy would be used.
Relying Parties MAY apply policy based on the SAML issuer's
<entityId>. In such cases, at least one of the following methods is
required in order to establish a relation between the SAML name and
the AAA name of the Identity Provider:
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o RADIUS realm in trusted digitally signed SAML response or
assertion.
o RADIUS realm in trusted SAML federation metadata.
A digitally signed SAML response alone is not sufficient for the same
reasons described above for SAML requests.
4.3.3. Mapping of AAA names in SAML metadata
This section defines the extensions to the SAML metadata
specification [OASIS.saml-metadata-2.0-os] that are required in order
to represent AAA names associated to a particular <EntityDescriptor>
element.
In SAML metadata, each single entity may act in many different roles
in the support of multiple profiles. This document defines two new
roles: RADIUS IDP and RADIUS RP, requiring the declaration of two new
subtypes of RoleDescriptorType: RADIUSIDPDescriptor and
RADIUSRPDescriptor. These subtypes define the additional elements
required to represent AAA names for IDP and RP entities respectively.
4.3.3.1. <RADIUSIDPDescriptor>
The <RADIUSIDPDescriptor> element extends RoleDescriptorType with
elements common to IdPs that support RADIUS. Its
RADIUSIDPDescriptorType complex type contains the following
additional elements:
<RADIUSIDPService> [Zero or More] Zero or more elements of type
EndpointType that describe RADIUS endpoints that are associated to
this Entity.
<RADIUSRealm> [Zero or More] Zero or more elements of type xs:string
that represent the acceptable values of the RADIUS realm
associated to this Entity, obtained from the realm part of RADIUS
User-Name attribute.
The following schema fragment defines the <RADIUSIDPDescriptor>
element and its RADIUSIDPDescriptorType complex type:
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<element name="RADIUSIDPDescriptor"
type="md:RADIUSIDPDescriptorType"/>
<complexType name="RADIUSIDPDescriptorType">
<complexContent>
<extension base="md:RoleDescriptorType">
<sequence>
<element ref="md:RADIUSIDPService"
minOccurs="0" maxOccurs="unbounded"/>
<element ref="md:RADIUSRealm"
minOccurs="0" maxOccurs="unbounded"/>
</sequence>
</extension>
</complexContent>
</complexType>
<element name="RADIUSIDPService" type="md:EndpointType"/>
<element name="RADIUSRealm" type="xs:string"/>
Figure 3: RADIUSIDPDescriptor schema
4.3.3.2. <RADIUSRPDescriptor>
The <RADIUSRPDescriptor> element extends RoleDescriptorType with
elements common to RPs that support RADIUS. Its
RADIUSRPDescriptorType complex type contains the following additional
elements:
<RADIUSRPService> [Zero or More] Zero or more elements of type
EndpointType that describe RADIUS endpoints that are associated to
this Entity.
<RADIUSNasIpAddress> [Zero or More] Zero or more elements of type
xs:string that represent the acceptable values of the RADIUS NAS-
IP-Address attribute associated to this Entity.
<RADIUSNasIdentifier> [Zero or More] Zero or more elements of type
xs:string that represent the acceptable values of the RADIUS NAS-
Identifier attribute associated to this Entity.
<RADIUSGssEapName> [Zero or More] Zero or more elements of type
xs:string that represent the acceptable values of the GSS-EAP
acceptor name associated to this Entity. The format for this name
is described in section 3.1 of [RFC7055], while section 3.4
describes how that name is decomposed and transported using RADIUS
attributes.
The following schema fragment defines the <RADIUSRPDescriptor>
element and its RADIUSRPDescriptorType complex type:
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<element name="RADIUSRPDescriptor"
type="md:RADIUSRPDescriptorType"/>
<complexType name="RADIUSRPDescriptorType">
<complexContent>
<extension base="md:RoleDescriptorType">
<sequence>
<element ref="md:RADIUSRPService"
minOccurs="0" maxOccurs="unbounded"/>
<element ref="md:RADIUSNasIpAddress"
minOccurs="0" maxOccurs="unbounded"/>
<element ref="md:RADIUSNasIdentifier"
minOccurs="0" maxOccurs="unbounded"/>
<element ref="md:RADIUSGssEapName"
minOccurs="0" maxOccurs="unbounded"/>
</sequence>
</extension>
</complexContent>
</complexType>
<element name="RADIUSRPService" type="md:EndpointType"/>
<element name="RADIUSNasIpAddress" type="xs:string"/>
<element name="RADIUSNasIdentifier" type="xs:string"/>
<element name="RADIUSGssEapName" type="xs:string"/>
Figure 4: RADIUSRPDescriptor schema
4.3.4. Example of SAML metadata including AAA names
The following figures illustrate an example of metadata including AAA
names for and IDP and a RP respectively. The IDP's SAML name is
"https://IdentityProvider.com/", whereas its RADIUS realm is
"idp.com". The RP's SAML name is "https://RelyingParty.com/SAML",
being its GSS-EAP acceptor name "nfs/fileserver.rp.com@RP.COM".
<EntityDescriptor xmlns="urn:oasis:names:tc:SAML:2.0:metadata"
entityID="https://IdentityProvider.com/SAML">
<RADIUSIDPDescriptor protocolSupportEnumeration=
"urn:oasis:names:tc:SAML:2.0:protocol">
<RADIUSRealm>
idp.com
</RADIUSRealm>
</RADIUSIDPDescriptor>
</EntityDescriptor>
Figure 5: Metadata for the IDP
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<EntityDescriptor xmlns="urn:oasis:names:tc:SAML:2.0:metadata"
entityID="https://RelyingParty.com/SAML">
<RADIUSRPDescriptor protocolSupportEnumeration=
"urn:oasis:names:tc:SAML:2.0:protocol">
<RADIUSGssEapName>
nfs/fileserver.rp.com@RP.COM
</RADIUSGssEapName>
</RADIUSRPDescriptor>
</EntityDescriptor>
Figure 6: Metadata for the RP
4.4. Use of XML Signatures
This binding calls for the use of SAML elements that support XML
signatures. To promote interoperability, implementations of this
binding MUST support a default configuration that does not require
the use of XML signatures. Implementations MAY choose to use XML
signatures.
4.5. Metadata Considerations
There are no metadata considerations particular to this binding,
because this binding and profiles of this binding are mostly intended
to be used without metadata. In this usage, RADIUS infrastructure is
used to provide integrity and naming of the SAML messages and
assertions. RADIUS configuration is used to provide policy,
including which attributes are accepted from a Relying Party and
which attributes are sent by an Identity Provider.
Nevertheless, implementations MAY support other configurations
including the use of metadata.
5. Network Access Identifier Name Identifier Format
URI: urn:ietf:params:abfab:nameid-format:nai
Indicates that the content of the element is in the form of a Network
Access Identifier (NAI) using the syntax described by [RFC7542].
6. RADIUS State Confirmation Method Identifiers
URI: urn:ietf:params:abfab:cm:user
URI: urn:ietf:params:abfab:cm:machine
Indicates that the Subject is the system entity (either the user or
machine) authenticated by a previously transmitted RADIUS Access-
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Accept message, as identified by the value of that RADIUS message's
State attribute.
7. ABFAB Authentication Profile
In the scenario supported by the ABFAB Authentication Profile, a
Client controlling a User Agent requests access to a Relying Party.
The Relying Party uses RADIUS to authenticate the Client. In
particular, the Relying Party, acting as a RADIUS client, attempts to
validate the Client's credentials against a RADIUS server acting as
the Client's Identity Provider. If the Identity Provider
successfully authenticates the Client, it produces an authentication
assertion which is consumed by the Relying Party. This assertion MAY
include a name identifier that can be used between the Relying Party
and the Identity Provider to refer to the Client.
7.1. Required Information
Identification: urn:ietf:params:abfab:profiles:authentication
Contact information: iesg@ietf.org
SAML Confirmation Method Identifiers: The SAML V2.0 "RADIUS State"
confirmation method identifiers, either urn:ietf:params:abfab:cm:user
or urn:ietf:params:abfab:cm:machine, are used by this profile.
Updates: None.
7.2. Profile Overview
To implement this scenario, a profile of the SAML Authentication
Request protocol is used in conjunction with the SAML RADIUS binding
defined in Section 4.
This profile is based on the SAML V2.0 Web Browser Single Sign-On
Profile [OASIS.saml-profiles-2.0-os]. There are some important
differences, specifically:
Authentication: This profile does not require the use of any
particular authentication method. The ABFAB architecture does
require the use of EAP [RFC3579], but this specification may be
used in other non-ABFAB scenarios.
Bindings: This profile does not use HTTP-based bindings. Instead
all SAML protocol messages are transported using the SAML RADIUS
binding defined in Section 4. This is intended to reduce the
number of bindings that implementations must support to be
interoperable.
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Requests: The profile does not permit the Relying Party to name the
<saml:Subject> of the <samlp:AuthnRequest>. This is intended to
simplify implementation and interoperability.
Responses: The profile only permits the Identity Provider to return
a single SAML message or assertion that MUST contain exactly one
authentication statement. Other statements may be included within
this assertion at the discretion of the Identity Provider. This
is intended to simplify implementation and interoperability.
Figure 7 below illustrates the flow of messages within this profile.
Client 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 7
1. Client request to Relying Party (Section 7.3.1): In step 1, the
Client, 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 Client exists and initiates the
authentication process.
2. Relying Party issues <samlp:AuthnRequest> to Identity Provider
(Section 7.3.2). In step 2, the Relying Party may optionally
issue a <samlp:AuthnRequest> message to be delivered to the
Identity Provider using the SAML-Message RADIUS attribute.
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3. Identity Provider identifies Client (Section 7.3.3). In step 3,
the Client is authenticated and identified by the Identity
Provider, while honoring any requirements imposed by the Relying
Party in the <samlp:AuthnRequest> message if provided.
4. Identity Provider issues <samlp:Response> to Relying Party
(Section 7.3.4). In step 4, the Identity Provider issues a
<samlp:Response> message to the Relying Party using the SAML
RADIUS binding. The response either indicates an error or
includes a SAML Authentication Statement in exactly one SAML
Assertion.
5. Relying Party grants or denies access to Client (Section 7.3.5).
In step 5, having received the response from the Identity
Provider, the Relying Party can respond to the Client with its
own error, or can establish its own security context for the
Client and return the requested resource.
7.3. 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 it, the former takes precedence.
7.3.1. Client Request to Relying Party
The profile is initiated by an arbitrary Client 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 RADIUS client, attempts to authenticate the
Client.
7.3.2. Relying Party Issues <samlp:AuthnRequest> to Identity Provider
The Relying Party uses RADIUS to communicate with the Client's
Identity Provider. The Relying Party MAY include a
<samlp:AuthnRequest> within this RADIUS Access-Request message using
the SAML-Message RADIUS attribute. The next hop destination MAY be
the Identity Provider or alternatively an intermediate RADIUS proxy.
Profile-specific rules for the contents of the <samlp:AuthnRequest>
element are given in Section 7.4.1.
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7.3.3. Identity Provider Identifies Client
The Identity Provider MUST establish the identity of the Client using
a RADIUS authentication method, or else it will return an error. If
the ForceAuthn attribute on the <samlp:AuthnRequest> element (if sent
by the Relying Party) 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 Client (for example, TLS state
that may be used for session resumption). Otherwise, and in all
other respects, the Identity Provider may use any method to
authenticate the Client, subject to the constraints called out in the
<samlp:AuthnRequest> message.
7.3.4. Identity Provider Issues <samlp:Response> to Relying Party
The Identity Provider MUST conclude the authentication in a manner
consistent with the RADIUS authentication result. The IdP MAY issue
a <samlp:Response> message to the Relying Party that is consistent
with the authentication result, as described in
[OASIS.saml-core-2.0-os]. This SAML response is delivered to the
Relying Party using the SAML RADIUS binding described in Section 4.
Profile-specific rules regarding the contents of the <samlp:Response>
element are given in Section 7.4.2.
7.3.5. Relying Party Grants or Denies Access to Client
If issued by the Identity Provider, the Relying Party MUST process
the <samlp:Response> message and any enclosed <saml:Assertion>
elements as described in [OASIS.saml-core-2.0-os]. Any subsequent
use of the <saml:Assertion> elements is at the discretion of the
Relying Party, subject to any restrictions contained within the
assertions themselves or from any previously established out-of-band
policy that governs the interaction between the Identity Provider and
the Relying Party.
7.4. 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 of that document, the Relying Party is the
requester, the User Agent is the attesting entity and the Client is
the Requested Subject.
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7.4.1. <samlp:AuthnRequest> Usage
The Relying Party MUST NOT include a <saml:Subject> element in the
request. The authenticated RADIUS identity identifies the Client to
the Identity Provider.
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 Relying Party wishes to permit the Identity Provider to
establish a new identifier for the Client if none exists, it MUST
include a <saml:NameIDPolicy> element with the AllowCreate attribute
set to "true". Otherwise, only a Client for whom the Identity
Provider has previously established an identifier usable by the
Relying Party can be authenticated successfully.
The <samlp:AuthnRequest> message MAY be signed. Authentication and
integrity are also provided by the SAML RADIUS binding.
7.4.2. <samlp:Response> Message Usage
If the Identity Provider cannot or will not satisfy the request, it
MUST either respond with a <samlp:Response> message containing an
appropriate error status code or codes and/or respond with a RADIUS
Access-Reject message.
If the Identity Provider wishes to return an error, it MUST NOT
include any assertions in the <samlp:Response message>. Otherwise,
if the request is successful (or if the response is not associated
with a request), the <samlp:Response> element is subject conform to
the following:
o It MAY be signed.
o It MUST contain exactly one <saml:Assertion>. The <saml:Subject>
element of this assertion MUST refer to the authenticated RADIUS
user.
o The assertion MUST contain a <saml:AuthnStatement>. Besides, the
assertion MUST contain a <saml:Subject> element with at least one
<saml:SubjectConfirmation> element containing a Method of
urn:ietf:params:abfab:cm:user or urn:ietf:params:abfab:cm:machine
that reflects the authentication of the Client to the Identity
Provider. Since the containing message is in response to an
<samlp:AuthnRequest>, the InResponseTo attribute MUST match the
request's ID. The <saml:Subject> element MAY use the NAI Name
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Identifier Format described in Section 5 to establish an
identifier between the Relying Party and the IdP.
o Other conditions MAY be included as requested by the Relying Party
or at the discretion of the Identity Provider. The Identity
Provider is NOT obligated to honor the requested set of conditions
in the <samlp:AuthnRequest>, if any.
7.4.3. <samlp:Response> Message Processing Rules
The Relying Party MUST do the following:
o Assume that the Client's identifier implied by a SAML <Subject>
element, if present, takes precedence over an identifier implied
by the RADIUS User-Name attribute.
o Verify that the InResponseTo attribute in the "RADIUS State"
<saml:SubjectConfirmationData> equals the ID of its original
<samlp:AuthnRequest> message, unless the response is unsolicited,
in which case the attribute MUST NOT be present.
o If a <saml:AuthnStatement> used to establish a security context
for the Client contains a SessionNotOnOrAfter attribute, the
security context SHOULD be discarded once this time is reached,
unless the Relying Party reestablishes the Client'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 Client.
7.4.4. Unsolicited Responses
An Identity Provider MAY initiate this profile by delivering an
unsolicited <saml:Assertion> to a Relying Party. This MUST NOT
contain any <saml:SubjectConfirmationData> elements containing an
InResponseTo attribute.
7.4.5. Use of the SAML RADIUS Binding
It is RECOMMENDED that the RADIUS exchange is protected using TLS
encryption for RADIUS [RFC6614] to provide confidentiality and
improve integrity protection.
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7.4.6. Use of XML Signatures
This profile calls for the use of SAML elements that support XML
signatures. To promote interoperability implementations of this
profile MUST NOT require the use of XML signatures. Implementations
MAY choose to use XML signatures.
7.4.7. Metadata Considerations
There are no metadata considerations particular to this binding.
8. ABFAB Assertion Query/Request Profile
This profile builds on the SAML V2.0 Assertion Query/Request Profile
defined by [OASIS.saml-profiles-2.0-os]. That profile describes the
use of the Assertion Query and Request Protocol defined by section
3.3 of [OASIS.saml-core-2.0-os] with synchronous bindings, such as
the SOAP binding defined in [OASIS.saml-bindings-2.0-os].
While the SAML V2.0 Assertion Query/Request Profile is independent of
the underlying binding, it is nonetheless useful to describe the use
of the SAML RADIUS binding defined in Section 4 of this document, in
the interests of promoting interoperable implementations,
particularly as the SAML V2.0 Assertion Query/Request Profile is most
frequently discussed and implemented in the context of the SOAP
binding.
8.1. Required Information
Identification: urn:ietf:params:abfab:profiles:query
Contact information: iesg@ietf.org
Description: Given below.
Updates: None.
8.2. Profile Overview
As with the SAML V2.0 Assertion Query/Request Profile defined by
[OASIS.saml-profiles-2.0-os] the message exchange and basic
processing rules that govern this profile are largely defined by
Section 3.3 of [OASIS.saml-core-2.0-os] that defines the messages to
be exchanged, in combination with the binding used to exchange the
messages. The SAML RADIUS binding described in this document defines
the binding of the message exchange to RADIUS. Unless specifically
noted here, all requirements defined in those specifications apply.
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Figure 8 below illustrates the basic template for the query/request
profile.
Relying Party Identity Provider
(SAML requester) (SAML responder)
| |
| (1) |
| - - - - - - - - - - - - - - - - - - - - - - - > |
| |
| (2) |
| < - - - - - - - - - - - - - - - - - - - - - - - |
| |
V V
The following steps are described by the profile.
Figure 8
1. Query/Request issued by Relying Party: In step 1, a Relying Party
initiates the profile by sending an <AssertionIDRequest>,
<SubjectQuery>, <AuthnQuery>, <AttributeQuery>, or
<AuthzDecisionQuery> message to a SAML authority.
2. <Response> issued by SAML Authority: In step 2, the responding
SAML authority (after processing the query or request) issues a
<Response> message to the Relying Party.
8.3. Profile Description
8.3.1. Differences from the SAML V2.0 Assertion Query/Request Profile
This profile is identical to the SAML V2.0 Assertion Query/Request
Profile, with the following exceptions:
o When processing the SAML request, the IdP MUST give precedence to
the Client's identifier implied by RADIUS State attribute, if
present, over the identifier implied by the SAML request's
<Subject>, if any.
o In respect to sections 6.3.1 and 6.5 of
[OASIS.saml-profiles-2.0-os], this profile does not consider the
use of metadata (as in [OASIS.saml-metadata-2.0-os]). See
Section 8.3.4.
o In respect to sections 6.3.2, 6.4.1, and 6.4.2 of
[OASIS.saml-profiles-2.0-os], this profile additionally stipulates
that implementations of this profile MUST NOT require the use of
XML signatures. See Section 8.3.3.
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8.3.2. Use of the SAML RADIUS Binding
The RADIUS Access-Request sent by the Relying Party:
o MUST include an instance of the RADIUS Service-Type attribute,
having a value of Authorize-Only.
o SHOULD include the RADIUS State attribute, where this Query/
Request pertains to previously authenticated Client.
When processing the SAML request, the IdP MUST give precedence to the
Client's identifier implied by RADIUS State attribute over the
identifier implied by the SAML request's <Subject>, if any.
It is RECOMMENDED that the RADIUS exchange is protected using TLS
encryption for RADIUS [RFC6614] to provide confidentiality and
improve integrity protection.
8.3.3. Use of XML Signatures
This profile calls for the use of SAML elements that support XML
signatures. To promote interoperability implementations of this
profile MUST NOT require the use of XML signatures. Implementations
MAY choose to use XML signatures.
8.3.4. Metadata Considerations
There are no metadata considerations particular to this binding.
9. Privacy considerations
The profiles defined in this document allow a Relying Party to
request specific information about the Client, and allow an IdP to
disclose information about that Client. In this sense, Identity
Providers MUST apply policy to decide what information is released to
a particular Relying Party. Moreover, the identity of the Client is
typically hidden from the Relying Party unless informed by the
Identity Provider. Conversely, the Relying Party does typically know
the realm of the IdP, as it is required to being able to route the
RADIUS packets to the right destination.
The kind of information that is released by the IdP MAY include
generic attributes such as affiliation shared by many Clients. But
even these generic attributes can help to identify a specific Client.
Other kind of attributes MAY also provide a Relying Party with the
ability to link the same Client between different sessions. Finally,
other kind of attributes MAY provide a group of Relying Parties with
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the ability to link the Client between them or with personally
identifiable information about the Client.
These profiles do not directly provide a Client with a mechanism to
express preferences about what information is released. That
information can be expressed out-of-band, for example as part of the
enrollment process.
The Relying Party MAY disclose privacy-sensitive information about
itself as part of the request, although this is unlikely in typical
deployments.
If RADIUS proxies are used and encryption is not used, the attributes
disclosed by the IdP are visible to the proxies. This is a
significant privacy exposure in some deployments. Ongoing work is
exploring mechanisms for creating TLS connections directly between
the RADIUS client and the RADIUS server to reduce this exposure. If
proxies are used, the impact of exposing SAML assertions to the
proxies needs to be carefully considered.
The use of TLS to provide confidentiality for the RADIUS exchange is
strongly encouraged. Without this, passive eavesdroppers can observe
the assertions.
10. Security Considerations
In this specification, the Relying Party MUST trust any statement in
the SAML messages from the IdP in the same way that it trusts
information contained in RADIUS attributes. These entities MUST
trust the RADIUS infrastructure to provide integrity of the SAML
messages.
Furthermore, the Relying Party MUST apply policy and filter the
information based on what information the IdP is permitted to assert
and on what trust is reasonable to place in proxies between them.
XML signatures and encryption are provided as an OPTIONAL mechanism
for end-to-end security. These mechanism can protect SAML messages
from being modified by proxies in the RADIUS infrastructure. These
mechanisms are not mandatory-to-implement. It is believed that
ongoing work to provide direct TLS connections between a RADIUS
client and RADIUS server will provide similar assurances but better
deployability. XML security is appropriate for deployments where
end-to-end security is required but proxies cannot be removed or
where SAML messages need to be verified at a later time or by parties
not involved in the authentication exchange.
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11. IANA Considerations
11.1. RADIUS Attributes
The authors request that Attribute Types and Attribute Values defined
in this document be registered by the Internet Assigned Numbers
Authority (IANA) from the RADIUS namespaces as described in the "IANA
Considerations" section of [RFC3575], in accordance with BCP 26
[RFC5226]. For RADIUS packets, attributes and registries created by
this document IANA is requested to place them at
http://www.iana.org/assignments/radius-types.
In particular, this document defines two new RADIUS attributes,
entitled "SAML-Assertion" and "SAML-Message" (see Section 3), with
assigned values of 245.TBD1 and 245.TBD2 from the Long Extended Space
of [RFC6929]:
Type Ext. Type Name Length Meaning
---- --------- -------------- ------ ------------------------
245 TBD1 SAML-Assertion >=5 Encodes a SAML assertion
245 TBD2 SAML-Message >=5 Encodes a SAML protocol
message
11.2. ABFAB Parameters
A new top-level registry is created titled "ABFAB Parameters".
In this top-level registry, a sub-registry titled "ABFAB 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 allow early registration related to specifications under
development when the community believes they have reached 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 a parameter named "paramname" is to be registered in this
registry, then its URN will be "urn:ietf:params:abfab:paramname".
The initial registrations are as follows:
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+-------------------------+-----------+
| Parameter | Reference |
+-------------------------+-----------+
| bindings:radius | Section 4 |
| nameid-format:nai | Section 5 |
| profiles:authentication | Section 7 |
| profiles:query | Section 8 |
| cm:user | Section 6 |
| cm:machine | Section 6 |
+-------------------------+-----------+
ABFAB Parameters
11.3. Registration of the ABFAB URN Namespace
IANA is requested to register the "abfab" URN sub-namespace in the
IETF URN sub-namespace for protocol parameters defined in [RFC3553].
Registry Name: abfab
Specification: draft-ietf-abfab-aaa-saml
Repository: ABFAB URN Parameters (Section Section 11.2)
Index Value: Sub-parameters MUST be specified in UTF-8 using standard
URI encoding where necessary.
12. Acknowledgements
The authors would like to acknowledge the OASIS Security Services
(SAML) Technical Committee, and Scott Cantor in particular, for their
help with the SAML-related material.
The authors would also like to acknowledge the collaboration of Jim
Schaad, Leif Johansson, Klaas Wierenga, Stephen Farell, Gabriel
Lopez, and Rafael Marin, who have provided valuable comments on this
document.
13. References
13.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
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[RFC2865] Rigney, C., Willens, S., Rubens, A., and W. Simpson,
"Remote Authentication Dial In User Service (RADIUS)",
RFC 2865, DOI 10.17487/RFC2865, June 2000,
<http://www.rfc-editor.org/info/rfc2865>.
[RFC3579] Aboba, B. and P. Calhoun, "RADIUS (Remote Authentication
Dial In User Service) Support For Extensible
Authentication Protocol (EAP)", RFC 3579,
DOI 10.17487/RFC3579, September 2003,
<http://www.rfc-editor.org/info/rfc3579>.
[RFC6614] Winter, S., McCauley, M., Venaas, S., and K. Wierenga,
"Transport Layer Security (TLS) Encryption for RADIUS",
RFC 6614, DOI 10.17487/RFC6614, May 2012,
<http://www.rfc-editor.org/info/rfc6614>.
[RFC6929] DeKok, A. and A. Lior, "Remote Authentication Dial In User
Service (RADIUS) Protocol Extensions", RFC 6929,
DOI 10.17487/RFC6929, April 2013,
<http://www.rfc-editor.org/info/rfc6929>.
[RFC3575] Aboba, B., "IANA Considerations for RADIUS (Remote
Authentication Dial In User Service)", RFC 3575,
DOI 10.17487/RFC3575, July 2003,
<http://www.rfc-editor.org/info/rfc3575>.
[RFC7542] DeKok, A., "The Network Access Identifier", RFC 7542,
DOI 10.17487/RFC7542, May 2015,
<http://www.rfc-editor.org/info/rfc7542>.
[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-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.
[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.
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[OASIS.saml-metadata-2.0-os]
Cantor, S., Moreh, J., Philpott, R., and E. Maler,
"Metadata for the Security Assertion Markup Language
(SAML) V2.0", OASIS Standard saml-metadata-2.0-os, March
2005.
13.2. Informative References
[RFC3553] Mealling, M., Masinter, L., Hardie, T., and G. Klyne, "An
IETF URN Sub-namespace for Registered Protocol
Parameters", BCP 73, RFC 3553, DOI 10.17487/RFC3553, June
2003, <http://www.rfc-editor.org/info/rfc3553>.
[RFC3588] Calhoun, P., Loughney, J., Guttman, E., Zorn, G., and J.
Arkko, "Diameter Base Protocol", RFC 3588,
DOI 10.17487/RFC3588, September 2003,
<http://www.rfc-editor.org/info/rfc3588>.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
DOI 10.17487/RFC5226, May 2008,
<http://www.rfc-editor.org/info/rfc5226>.
[RFC7055] Hartman, S., Ed. and J. Howlett, "A GSS-API Mechanism for
the Extensible Authentication Protocol", RFC 7055,
DOI 10.17487/RFC7055, December 2013,
<http://www.rfc-editor.org/info/rfc7055>.
[RFC7499] Perez-Mendez, A., Ed., Marin-Lopez, R., Pereniguez-Garcia,
F., Lopez-Millan, G., Lopez, D., and A. DeKok, "Support of
Fragmentation of RADIUS Packets", RFC 7499,
DOI 10.17487/RFC7499, April 2015,
<http://www.rfc-editor.org/info/rfc7499>.
[I-D.ietf-abfab-arch]
Howlett, J., Hartman, S., Tschofenig, H., Lear, E., and J.
Schaad, "Application Bridging for Federated Access Beyond
Web (ABFAB) Architecture", draft-ietf-abfab-arch-13 (work
in progress), July 2014.
[I-D.ietf-radext-bigger-packets]
Hartman, S., "Larger Packets for RADIUS over TCP", draft-
ietf-radext-bigger-packets-03 (work in progress), March
2015.
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Authors' Addresses
Josh Howlett
Janet
Lumen House, Library Avenue, Harwell
Oxford OX11 0SG
UK
Phone: +44 1235 822363
EMail: Josh.Howlett@ja.net
Sam Hartman
Painless Security
EMail: hartmans-ietf@mit.edu
Alejandro Perez-Mendez (editor)
University of Murcia
Campus de Espinardo S/N, Faculty of Computer Science
Murcia 30100
Spain
Phone: +34 868 88 46 44
EMail: alex@um.es
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