ABFAB M. Jones
Internet-Draft Bridgewater Systems
Intended status: Informational H. Tschofenig
Expires: September 13, 2012 Nokia Siemens Networks
March 12, 2012
The Diameter 'Application Bridging for Federated Access Beyond Web
(ABFAB)' Application
draft-jones-diameter-abfab-01.txt
Abstract
The Application Bridging for Federated Access Beyond Web (ABFAB)
architecture provides cross-domain authentication, authorization and
accounting functionality by utilizing well-established technologies,
such as Diameter, the Extensible Authentication Protocol (EAP), and
the Generic Security Services API (GSS-API).
This document defines a Diameter application for usage with the ABFAB
architecture to convey authentication information, and authorization
decisions from the Diameter server (acting as the identity provider)
to the Diameter client (acting as a relying party) encoded in a
Security Assertion Markup Language (SAML) encoding.
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
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This Internet-Draft will expire on September 13, 2012.
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
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 6
3. Application Identifiers . . . . . . . . . . . . . . . . . . . 7
4. Protocol Description . . . . . . . . . . . . . . . . . . . . . 8
4.1. Session Management . . . . . . . . . . . . . . . . . . . . 8
4.1.1. Session-Termination-Request . . . . . . . . . . . . . 9
4.1.2. Session-Termination-Answer . . . . . . . . . . . . . . 9
4.1.3. Abort-Session-Request . . . . . . . . . . . . . . . . 9
4.1.4. Abort-Session-Answer . . . . . . . . . . . . . . . . . 9
4.2. Accounting for ABFAB services . . . . . . . . . . . . . . 9
4.2.1. Accounting-Request . . . . . . . . . . . . . . . . . . 10
4.2.2. Accounting-Answer . . . . . . . . . . . . . . . . . . 10
5. Command Codes . . . . . . . . . . . . . . . . . . . . . . . . 11
5.1. Diameter-EAP-Request . . . . . . . . . . . . . . . . . . . 11
5.2. Diameter-EAP-Answer . . . . . . . . . . . . . . . . . . . 12
6. AVPs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
7. Result-Code AVP Values . . . . . . . . . . . . . . . . . . . . 14
8. AVP Occurrence Tables . . . . . . . . . . . . . . . . . . . . 15
8.1. DER, DEA AVP/Command-Code Table . . . . . . . . . . . . . 15
8.2. Coupled Accounting Model AVP Table . . . . . . . . . . . . 15
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17
9.1. AVP Codes . . . . . . . . . . . . . . . . . . . . . . . . 17
9.2. Application Identifier . . . . . . . . . . . . . . . . . . 17
10. Security Considerations . . . . . . . . . . . . . . . . . . . 18
11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 19
12. Normative References . . . . . . . . . . . . . . . . . . . . . 20
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 21
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1. Introduction
The Application Bridging for Federated Access Beyond Web (ABFAB)
architecture [I-D.ietf-abfab-arch] provides cross-domain
authentication, authorization and accounting functionality by
utilizing well-established technologies, such as Diameter, the
Extensible Authentication Protocol (EAP), and the Generic Security
Services API (GSS-API).
The steps taken generally in an ABFAB federated authentication/
authorization exchange are as follows:
1. Principal provides NAI to Application: Somehow the client is
configured with at least the realm portion of an NAI, which
represents the IdP to be discovered.
2. Authentication mechanism selection: this is the step necessary
to indicate that the GSS-EAP SASL/GS2 mechanism will be used for
authentication/authorization.
3. Client Application provides NAI to RP: At the conclusion of
mechanism selection the NAI must be provided to the RP for
discovery.
4. Discovery of federated IdP: This is discussed in detail below.
Either the RP is configured with authorized IdPs, or it makes
use of a federation proxy.
5. Request from Relying Party to IdP: Once the RP knows who the IdP
is, it or its agent will forward RADIUS request that
encapsulates a GSS/EAP access request to an IdP. This may or
may not contain a SAML request as a series of attributes. At
this stage, the RP will likely have no idea who the principal
is. The RP claims its identity to the IdP in AAA attributes,
and it makes whatever SAML Attribute Requests through a AAA
attribute.
6. IdP informs the principal of which EAP method to use: The
available and appropriate methods are discussed below in this
memo.
7. A bunch of EAP messages happen between the endpoints: Messages
are exchanged between the principal and the IdP until a result
is determined. The number and content of those messages will
depend on the EAP method. If the IdP is unable to authenticate
the principal, the process concludes here. As part of this
process, the principal will, under protection of EAP, assert the
identity of the RP to which it intends to authenticate.
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8. Successful Authentication: At the very least the IdP (its EAP
server) and EAP peer / subject have authenticated one another.
As a result of this step, the subject and the IdP hold two
cryptographic keys- a Master Session Key (MSK), and an Extended
MSK (EMSK). If the asserted identity of the RP by the principal
matches the identity the RP itself asserted, there is some
confidence that the RP is now authenticated to the IdP.
9. Local IdP Policy Check: At this stage, the IdP checks local
policy to determine whether the RP and subject are authorized
for a given transaction/service, and if so, what if any,
attributes will be released to the RP. Additional policy checks
will likely have been made earlier just through the process of
discovery.
10. Response from the IdP to the Relying Party: Once the IdP has
made a determination of whether and how to authenticate or
authorize the principal to the RP, it returns either a negative
AAA result to the RP, or it returns a positive result to the RP,
along with an optional set of AAA attributes associated with the
principal that could include one or more SAML assertions. In
addition, an EAP MSK is returned to the subject.
11. RP Processes Results. When the RP receives the result from the
IdP, it should have enough information to either grant or refuse
a resource access request. It may have information that leads
it to make additional attribute queries. It may have
information that associates the principal with specific
authorization identies. It will apply these results in an
application-specific way.
12. RP returns results to principal: Once the RP has a response it
must inform the client application of the result. If all has
gone well, all are authenticated, and the application proceeds
with appropriate authorization levels.
The involved entities are shown in Figure 1.
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+--------------+
| AAA Server |
| (Identity |
| Provider) |
+-^----------^-+
* EAP | RADIUS/
* | Diameter
--v----------v--
/// \\\
// \\ ***
| Federation | back-
| | end
\\ // ***
\\\ ///
--^----------^--
* EAP | RADIUS/
Application * | Diameter
+-------------+ Data +-v----------v--+
| |<---------------->| |
| Client | EAP/EAP Method | Server Side |
| Application |<****************>| Application |
| @ End Host | GSS-API |(Relying Party)|
| |<---------------->| |
| | Application | |
| | Protocol | |
| |<================>| |
+-------------+ +---------------+
*** front-end ***
Legend:
<****>: End-to-end exchange
<---->: Hop-by-hop exchange
<====>: Protocol through which GSS-API/GS2 exchanges are tunnelled
Figure 1: Architecture for Federated Access of non-Web based
Applications
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2. Terminology
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].
This document uses terminology defined [I-D.ietf-abfab-arch].
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3. Application Identifiers
This specification defines a new Diameter application and the
respective Application Identifier:
Diameter ABFAB (ABFAB) [[TBD by IANA]]
The Diameter ABFAB related accounting information generated by the
Diameter client uses the ABFAB Application Identifier in the case of
coupled accounting model. The Diameter Base Accounting Application
Identifier (value of 3) is used in case of the split accounting
model. Refer to Section 4.2 for more information regarding the
accounting models.
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4. Protocol Description
Relying Party Client App IdP
| (1) | Client App gets NAI (somehow)
| | |
|<-----(2)----->| | Mechanism Selection
| | |
|<-----(3)-----<| | NAI transmitted to RP
| | |
|<=====(4)====================>| Discovery
| | |
|>=====(5)====================>| Access request from RP to IdP
| | |
| |< - - (6) - -<| EAP method to Principal
| | |
| |< - - (7) - ->| EAP Exchange to authenticate
| | | Principal
| | |
| | (8 & 9) Local Policy Check
| | |
|<====(10)====================<| IdP Assertion to RP
| | |
| | | (11) RP Processes results.
| | |
|>----(12)----->| | Results to client app.
----- = Between Client App and RP
===== = Between RP and IdP
- - - = Between Client App and IdP
Figure 2: Message Interaction Sequence
4.1. Session Management
The Diameter server may maintain state or may be stateless. This is
indicated in the Auth-Session-State AVP (or its absence). The
Diameter client MUST support the Authorization Session State Machine
defined in [RFC3588].
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4.1.1. Session-Termination-Request
The Session-Termination-Request (STR) message [RFC3588] is sent by
the Diameter client to inform the Diameter server that an authorized
session is being terminated.
4.1.2. Session-Termination-Answer
The Session-Termination-Answer (STA) message [RFC3588] is sent by the
Diameter server to acknowledge the notification that the session has
been terminated.
4.1.3. Abort-Session-Request
The Abort-Session-Request (ASR) message [RFC3588] is sent by the
Diameter server to the Diameter client to terminate the authorized
session. When the Diameter client receives the ASR message, it MUST
take further actions to terminate the established application
context.
4.1.4. Abort-Session-Answer
The Abort-Session-Answer (ASA) message [RFC3588] is sent by the Home
Agent in response to an ASR message.
4.2. Accounting for ABFAB services
The Diameter client collects accounting records needed for service
control and charging MUST support the accounting procedures and the
Accounting Session State Machine as defined in [RFC3588].
The Diameter application design guideline
[I-D.ietf-dime-app-design-guide] defines two separate models for
accounting:
Split accounting model:
According to this model, the accounting messages use the Diameter
Base Accounting Application Identifier (value of 3). Since
accounting is treated as an independent application, accounting
commands may be routed separately from the rest of application
messages and thus the accounting messages generally end up in a
central accounting server. Since the Diameter ABFAB application
does not define its own unique accounting commands, this is the
preferred choice, since it permits use of centralized accounting
for several applications.
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Coupled accounting model:
In this model, the accounting messages will use the ABFAB
Application Identifiers. This means that accounting messages will
be routed like any other Diameter ABFAB application messages.
This requires the Diameter server in charge of the Diameter ABFAB
application to handle the accounting records (e.g., sends them to
a proper accounting server).
As mentioned above, the preferred choice is to use the split
accounting model and thus to choose Diameter Base Accounting
Application Identifier (value of 3) for accounting messages.
4.2.1. Accounting-Request
The Accounting-Request command [RFC3588] is sent by the Diameter
client to the Diameter server to exchange accounting information.
4.2.2. Accounting-Answer
The Accounting-Answer command [RFC3588] is sent by the Diameter
server to the Diameter client to acknowledge an Accounting-Request.
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5. Command Codes
The Diameter ABFAB application defined in this document reuses the
Diameter EAP application [RFC4072] commands: Diameter-EAP-Request
(DER) and Diameter-EAP-Answer (DEA). This specification extends the
existing DER and DEA command ABNFs to offer the necessary ABFAB
functionality. Other than new additional AVPs and the corresponding
additions to the command ABNFs, the Diameter EAP application command
ABNFs remain unchanged. The ABNF language is defined in [RFC3588].
Command-Name Abbrev. Code Reference
---------------------------------------------
Diameter-EAP-Request DER 268 RFC 4072
Diameter-EAP-Answer DEA 268 RFC 4072
Figure 3: Command Codes
5.1. Diameter-EAP-Request
The Diameter-EAP-Request (DER) message, indicated by the Command-Code
field set to 268 and the 'R' bit set in the Command Flags field, is
sent by the Diameter client to the Diameter server to initiate a
Diameter ABFAB authentication and authorization procedure. The
Application-ID field of the Diameter Header MUST be set to the
Diameter ABFAB Application ID (value of TDB).
<Diameter-EAP-Request> ::= < Diameter Header: 268, REQ, PXY >
< Session-Id >
{ Auth-Application-Id }
{ Origin-Host }
{ Origin-Realm }
{ Destination-Realm }
{ Auth-Request-Type }
[ Destination-Host ]
[ NAS-Identifier ]
[ NAS-IP-Address ]
[ NAS-IPv6-Address ]
[ NAS-Port-Type ]
[ User-Name ]
...
{ EAP-Payload }
...
[ SAML-AuthnRequest ]
...
* [ AVP ]
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The SAML-AuthnRequest AVP is only included in the first DER message
send by the Diameter client. The user is both authenticated and
during the EAP method authentication. Authorization happens
immediately after the authentication procedure has been completed.
Thus, the Auth-Request-Type AVP MUST be set to the value
AUTHORIZE_AUTHENTICATE.
5.2. Diameter-EAP-Answer
The Diameter-EAP-Answer (DEA) message, indicated by the Command-Code
field set to 268 and 'R' bit cleared in the Command Flags field, is
sent in response to the Diameter-EAP-Request message (DER). The
Application-Id field in the Diameter message header MUST be set to
the Diameter ABFAB Application-Id (value of TBD).
<Diameter-EAP-Answer> ::= < Diameter Header: 268, PXY >
< Session-Id >
{ Auth-Application-Id }
{ Auth-Request-Type }
{ Result-Code }
{ Origin-Host }
{ Origin-Realm }
[ User-Name ]
[ EAP-Payload ]
[ EAP-Reissued-Payload ]
[ EAP-Master-Session-Key ]
[ EAP-Key-Name ]
[ Multi-Round-Time ]
...
[ SAML-AuthnResponse ]
[ SAML-Assertion ]
...
* [ AVP ]
SAML related attributes are only included in the final message
exchange. Either the SAML-AuthnResponse AVP is included in the
response or a SAML-Assertion but not both.
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6. AVPs
+--------------------+
| AVP Flag rules |
+----+---+------+----+----+
AVP | | |SHOULD|MUST|MAY |
Attribute Name Code Value Type |MUST|MAY| NOT | NOT|Encr|
+-------------------------------------+----+---+------+----+----+
|SAML-Assertion TBD UTF8String | | P | | V | Y |
+-------------------------------------+----+---+------+----+----+
|SAML-AuthnRequest TBD UTF8String | | P | | V | Y |
+-------------------------------------+----+---+------+----+----+
|SAML-AuthnResponse TBD UTF8String | | P | | V | Y |
+-------------------------------------+----+---+------+----+----+
AVPs for the Diameter ABFAB Application
[Editor's Note: SAML encryption requirements are FFS. The "MAY Encr"
column in the above table refers to XML-Enc rather than the defunct
Diameter AVP encryption.]
The SAML-Assertion AVP contains the UTF8String encoded SAML
assertion.
The SAML-AuthnRequest AVP contains the UTF8String encoded SAML
AuthnRequest message.
The SAML-AuthnResponse AVP contains the UTF8String encoded SAML
AuthnResponse message.
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7. Result-Code AVP Values
This section defines new Result-Code [RFC3588] values that MUST be
supported by all Diameter implementations that conform to this
specification.
[Editor's Note: ABFAB specific error values may need to be added
here.]
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8. AVP Occurrence Tables
The following tables present the AVPs defined in this document and
their occurrences in Diameter messages.
The table uses the following symbols:
0:
The AVP MUST NOT be present in the message.
0+:
Zero or more instances of the AVP MAY be present in the message.
0-1:
Zero or one instance of the AVP MAY be present in the message.
1:
One instance of the AVP MUST be present in the message.
8.1. DER, DEA AVP/Command-Code Table
+------------+
|Command-Code|
|-----+------+
AVP Name | DER | DEA |
-------------------------------|-----+------+
SAML-Assertion | 0 | 1 |
SAML-AuthnRequest | 1 | 0 |
SAML-AuthnResponse | 0 | 1 |
+-----+------+
[Editor's Note: Is it possible to return more than one SAML-
Assertion?]
8.2. Coupled Accounting Model AVP Table
The table in this section is used to represent which AVPs defined in
this document are to be present in the Accounting messages, as
defined in [RFC3588].
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+-------------+
| Command-Code|
|------+------+
Attribute Name | ACR | ACA |
-------------------------------------|------+------+
Accounting-Input-Octets | 0-1 | 0-1 |
Accounting-Input-Packets | 0-1 | 0-1 |
Accounting-Output-Octets | 0-1 | 0-1 |
Accounting-Output-Packets | 0-1 | 0-1 |
Acct-Multi-Session-Id | 0-1 | 0-1 |
Acct-Session-Time | 0-1 | 0-1 |
-------------------------------------|------+------+
[Editor's Note: Do we need any application specific accounting
messages for ABFAB?]
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9. IANA Considerations
This section contains the namespaces that have either been created in
this specification or had their values assigned to existing
namespaces managed by IANA.
9.1. AVP Codes
This specification requires IANA to register the following new AVPs
from the AVP Code namespace defined in [RFC3588].
o SAML-Assertion
o SAML-AuthnRequest
o SAML-AuthnResponse
The AVPs are defined in Section 8.
9.2. Application Identifier
This specification requires IANA to allocate a new application ID
from the Application Identifier namespace defined in [RFC3588].
Application Identifier | Value
-----------------------------------+------
Diameter ABFAB (ABFAB) | TBD
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10. Security Considerations
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11. Acknowledgments
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12. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3588] Calhoun, P., Loughney, J., Guttman, E., Zorn, G., and J.
Arkko, "Diameter Base Protocol", RFC 3588, September 2003.
[RFC4072] Eronen, P., Hiller, T., and G. Zorn, "Diameter Extensible
Authentication Protocol (EAP) Application", RFC 4072,
August 2005.
[I-D.ietf-dime-app-design-guide]
Fajardo, V., Tschofenig, H., and L. Morand, "Diameter
Applications Design Guidelines",
draft-ietf-dime-app-design-guide-13 (work in progress),
January 2012.
[I-D.ietf-abfab-arch]
Howlett, J., Hartman, S., Tschofenig, H., and E. Lear,
"Application Bridging for Federated Access Beyond Web
(ABFAB) Architecture", draft-ietf-abfab-arch-01 (work in
progress), March 2012.
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Authors' Addresses
Mark Jones
Bridgewater Systems
Email: mark@azu.ca
Hannes Tschofenig
Nokia Siemens Networks
Linnoitustie 6
Espoo 02600
Finland
Phone: +358 (50) 4871445
Email: Hannes.Tschofenig@gmx.net
URI: http://www.tschofenig.priv.at
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