< draft-ietf-abfab-arch-02.txt   draft-ietf-abfab-arch-03.txt >
ABFAB J. Howlett ABFAB J. Howlett
Internet-Draft JANET(UK) Internet-Draft JANET(UK)
Intended status: Informational S. Hartman Intended status: Informational S. Hartman
Expires: November 25, 2012 Painless Security Expires: January 10, 2013 Painless Security
H. Tschofenig H. Tschofenig
Nokia Siemens Networks Nokia Siemens Networks
E. Lear E. Lear
Cisco Systems GmbH Cisco Systems GmbH
J. Schaad J. Schaad
Soaring Hawk Consulting Soaring Hawk Consulting
May 24, 2012 July 9, 2012
Application Bridging for Federated Access Beyond Web (ABFAB) Application Bridging for Federated Access Beyond Web (ABFAB)
Architecture Architecture
draft-ietf-abfab-arch-02.txt draft-ietf-abfab-arch-03.txt
Abstract Abstract
Over the last decade a substantial amount of work has occurred in the Over the last decade a substantial amount of work has occurred in the
space of federated access management. Most of this effort has space of federated access management. Most of this effort has
focused on two use-cases: network and web-based access. However, the focused on two use-cases: network and web-based access. However, the
solutions to these use-cases that have been proposed and deployed solutions to these use-cases that have been proposed and deployed
tend to have few common building blocks in common. tend to have few common building blocks in common.
This memo describes an architecture that makes use of extensions to This memo describes an architecture that makes use of extensions to
skipping to change at page 2, line 7 skipping to change at page 2, line 7
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on November 25, 2012. This Internet-Draft will expire on January 10, 2013.
Copyright Notice Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
skipping to change at page 3, line 13 skipping to change at page 3, line 13
described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 5 1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 5
1.2. An Overview of Federation . . . . . . . . . . . . . . . . 6 1.2. An Overview of Federation . . . . . . . . . . . . . . . . 6
1.3. Challenges to Contemporary Federation . . . . . . . . . . 9 1.3. Challenges to Contemporary Federation . . . . . . . . . . 9
1.4. An Overview of ABFAB-based Federation . . . . . . . . . . 9 1.4. An Overview of ABFAB-based Federation . . . . . . . . . . 9
1.5. Design Goals . . . . . . . . . . . . . . . . . . . . . . . 12 1.5. Design Goals . . . . . . . . . . . . . . . . . . . . . . . 12
1.6. Client to Relying Party Transport . . . . . . . . . . . . 13 1.6. Use of AAA . . . . . . . . . . . . . . . . . . . . . . . . 13
1.7. Use of AAA . . . . . . . . . . . . . . . . . . . . . . . . 14 1.7. Use of GSS-API . . . . . . . . . . . . . . . . . . . . . . 14
2. Architecture . . . . . . . . . . . . . . . . . . . . . . . . . 15 2. Architecture . . . . . . . . . . . . . . . . . . . . . . . . . 15
2.1. Relying Party to Identity Provider . . . . . . . . . . . . 16 2.1. Relying Party to Identity Provider . . . . . . . . . . . . 16
2.2. Client To Identity Provider . . . . . . . . . . . . . . . 19 2.1.1. AAA, RADIUS and Diameter . . . . . . . . . . . . . . . 17
2.3. Client to Relying Party . . . . . . . . . . . . . . . . . 20 2.1.2. Discovery and Rules Determination . . . . . . . . . . 18
3. Application Security Services . . . . . . . . . . . . . . . . 23 2.1.3. Routing and Technical Trust . . . . . . . . . . . . . 19
3.1. Authentication . . . . . . . . . . . . . . . . . . . . . . 23 2.1.4. SAML Assertions . . . . . . . . . . . . . . . . . . . 20
3.2. GSS-API Channel Binding . . . . . . . . . . . . . . . . . 24 2.2. Client To Identity Provider . . . . . . . . . . . . . . . 22
3.3. Host-Based Service Names . . . . . . . . . . . . . . . . . 25 2.2.1. Extensible Authentication Protocol (EAP) . . . . . . . 22
3.4. Per-Message Tokens . . . . . . . . . . . . . . . . . . . . 26 2.2.2. Channel Binding . . . . . . . . . . . . . . . . . . . 23
4. Future Work: Attribute Providers . . . . . . . . . . . . . . . 27 2.3. Client to Relying Party . . . . . . . . . . . . . . . . . 23
5. Privacy Considerations . . . . . . . . . . . . . . . . . . . . 28 2.3.1. GSS-API . . . . . . . . . . . . . . . . . . . . . . . 24
5.1. What Entities collect and use Data? . . . . . . . . . . . 28 2.3.2. Protocol Transport . . . . . . . . . . . . . . . . . . 25
5.2. Relationship between User's and other Entities . . . . . . 29 3. Application Security Services . . . . . . . . . . . . . . . . 26
3.1. Authentication . . . . . . . . . . . . . . . . . . . . . . 26
3.2. GSS-API Channel Binding . . . . . . . . . . . . . . . . . 27
3.3. Host-Based Service Names . . . . . . . . . . . . . . . . . 28
3.4. Per-Message Tokens . . . . . . . . . . . . . . . . . . . . 29
4. Future Work: Attribute Providers . . . . . . . . . . . . . . . 30
5. Privacy Considerations . . . . . . . . . . . . . . . . . . . . 31
5.1. What Entities collect and use Data? . . . . . . . . . . . 31
5.2. Relationship between User's and other Entities . . . . . . 32
5.3. What Data about the User is likely Needed to be 5.3. What Data about the User is likely Needed to be
Collected? . . . . . . . . . . . . . . . . . . . . . . . . 29 Collected? . . . . . . . . . . . . . . . . . . . . . . . . 32
5.4. What is the Identification Level of the Data? . . . . . . 29 5.4. What is the Identification Level of the Data? . . . . . . 32
5.5. Privacy Challenges . . . . . . . . . . . . . . . . . . . . 30 5.5. Privacy Challenges . . . . . . . . . . . . . . . . . . . . 33
6. Deployment Considerations . . . . . . . . . . . . . . . . . . 31 6. Deployment Considerations . . . . . . . . . . . . . . . . . . 34
6.1. EAP Channel Binding . . . . . . . . . . . . . . . . . . . 31 6.1. EAP Channel Binding . . . . . . . . . . . . . . . . . . . 34
6.2. AAA Proxy Behavior . . . . . . . . . . . . . . . . . . . . 31 6.2. AAA Proxy Behavior . . . . . . . . . . . . . . . . . . . . 34
7. Security Considerations . . . . . . . . . . . . . . . . . . . 32 7. Security Considerations . . . . . . . . . . . . . . . . . . . 35
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 34 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 37
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 35 9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 38
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 36 10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 39
10.1. Normative References . . . . . . . . . . . . . . . . . . . 36 10.1. Normative References . . . . . . . . . . . . . . . . . . . 39
10.2. Informative References . . . . . . . . . . . . . . . . . . 36 10.2. Informative References . . . . . . . . . . . . . . . . . . 40
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 40 Editorial Comments . . . . . . . . . . . . . . . . . . . . . . . .
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 44
1. Introduction 1. Introduction
The Internet uses numerous security mechanisms to manage access to The Internet uses numerous security mechanisms to manage access to
various resources. These mechanisms have been generalized and scaled various resources. These mechanisms have been generalized and scaled
over the last decade through mechanisms such as Simple Authentication over the last decade through mechanisms such as Simple Authentication
and Security Layer (SASL) with the Generic Security Server and Security Layer (SASL) with the Generic Security Server
Application Program Interface (GSS-API) (known as the GS2 family) Application Program Interface (GSS-API) (known as the GS2 family)
[RFC5801], Security Assertion Markup Language (SAML) [RFC5801], Security Assertion Markup Language (SAML)
[OASIS.saml-core-2.0-os], RADIUS [RFC2865], and Diameter [RFC3588]. [OASIS.saml-core-2.0-os], RADIUS [RFC2865], and Diameter [RFC3588].
skipping to change at page 4, line 42 skipping to change at page 4, line 42
[RFC5849], [I-D.ietf-oauth-v2] and WS-Trust [WS-TRUST]. The benefits [RFC5849], [I-D.ietf-oauth-v2] and WS-Trust [WS-TRUST]. The benefits
of federated access management include: of federated access management include:
Single or Simplified sign-on: Single or Simplified sign-on:
An Internet service can delegate access management, and the An Internet service can delegate access management, and the
associated responsibilities such as identity management and associated responsibilities such as identity management and
credentialing, to an organisation that already has a long-term credentialing, to an organisation that already has a long-term
relationship with the Subject. This is often attractive for relationship with the Subject. This is often attractive for
Relying Parties who frequently do not want these responsibilities. Relying Parties who frequently do not want these responsibilities.
The Subject may also therefore require fewer credentials, which is The Subject also requires fewer credentials, which is also
often desirable. desirable.
Privacy: Privacy:
Often a Relying Party does not need to know the identity of a Often a Relying Party does not need to know the identity of a
Subject to reach an access management decision. It is frequently Subject to reach an access management decision. It is frequently
only necessary for the Relying Party to establish, for example, only necessary for the Relying Party know specific attributes
that the Subject is affiliated with a particular organisation or about the subject, for example, that the Subject is affiliated
has a certain role or entitlement. Sometimes the RP does require with a particular organisation or has a certain role or
an identifier for the Subject (for example, so that it can entitlement. Sometimes the RP does not need to know the identity
recognise the Subject subsequently); in this case, it is a common of the Subject, but does require a unique identifier for the
practise for the IdP to only release a pseudonym that is specific Subject (for example, so that it can recognise the Subject
to that particular Relying Party. Federated access management subsequently); in this case, it is a common practise for the IdP
therefore provides various strategies for protecting the Subject's to only release a pseudonym that is specific to that particular
privacy. Other privacy aspects typically of concern are the Relying Party. Federated access management therefore provides
policy for releasing personal data about the Subject from the IdP various strategies for protecting the Subject's privacy. Other
to the RP, the purpose of the usage, the retention period of the privacy aspects typically of concern are the policy for releasing
data, and many more. personal data about the Subject from the IdP to the RP, the
purpose of the usage, the retention period of the data, and many
more.
Provisioning Provisioning
Sometimes a Relying Party needs, or would like, to know more about Sometimes a Relying Party needs, or would like, to know more about
a subject than an affiliation or a pseudonym. For example, a a subject than an affiliation or a pseudonym. For example, a
Relying Party may want the Subject's email address or name. Some Relying Party may want the Subject's email address or name. Some
federated access management technologies provide the ability for federated access management technologies provide the ability for
the IdP to supply this information, either on request by the RP or the IdP to supply this information, either on request by the RP or
unsolicited. unsolicited.
skipping to change at page 5, line 48 skipping to change at page 5, line 50
pseudonymity, unlinkability, and anonymity. pseudonymity, unlinkability, and anonymity.
In this architecture the IdP consists of the following components: an In this architecture the IdP consists of the following components: an
EAP server, a RADIUS or a Diameter server, and optionally a SAML EAP server, a RADIUS or a Diameter server, and optionally a SAML
Assertion service. Assertion service.
This document uses the term Network Access Identifier (NAI), as This document uses the term Network Access Identifier (NAI), as
defined in [RFC4282]. defined in [RFC4282].
One of the problems people will find with reading this document is One of the problems people will find with reading this document is
that the terminology somestimes appears to be inconsistant. This is that the terminology sometimes appears to be inconsistent. This is
do the fact that the terms used by the different standards we are due the fact that the terms used by the different standards we are
picking up don't use the same terms. In general the document uses picking up don't use the same terms. In general the document uses
either a consistant term or the term associated with the standard either a consistent term or the term associated with the standard
under discussion as appropriate. For reference we include this table under discussion as appropriate. For reference we include this table
which maps the different terms into a single table. which maps the different terms into a single table.
+----------+------------+-------------------+-----------------------+ +----------+------------+-------------------+-----------------------+
| Protocol | Subject | Relying Party | Identity Provider | | Protocol | Subject | Relying Party | Identity Provider |
+----------+------------+-------------------+-----------------------+ +----------+------------+-------------------+-----------------------+
| ABFAB | Subject | Relying Party | Identity Provider | | ABFAB | Subject | Relying Party | Identity Provider |
| | | (RP) | (IdP) | | | | (RP) | (IdP) |
| | | | | | | | | |
| | Principal | | | | | Principal | | |
| | | | | | | | | |
| SAML | | | | | | Client | | |
| | | | | | | | | |
| GSS-API | | | | | SAML | Subject | Service Provider | Issuer |
| | | | | | | | | |
| EAP | EAP client | | EAP server | | GSS-API | Initiator | Acceptor | |
| | | | | | | | | |
| | EAP peer | | | | EAP | EAP client | | EAP server |
| | | | | | | | | |
| SASL | | | | | | EAP peer | | |
| | | | | | | | | |
| AAA | | AAA Client | AAA server | | SASL | | | |
| | | | | | | | | |
| RADIUS | client | NAS | RADIUS server | | AAA | | AAA Client | AAA server |
| | | | |
| RADIUS | client | NAS | RADIUS server |
+----------+------------+-------------------+-----------------------+ +----------+------------+-------------------+-----------------------+
Note that in some cases a cell has been left empty, in these cases Note that in some cases a cell has been left empty, in these cases
there is no direct name that represents this concept. there is no direct name that represents this concept.
Note to reviewers - I have most likely missed some entries in the Note to reviewers - I have most likely missed some entries in the
table. Please provide me with both correct names from the protocol table. Please provide me with both correct names from the protocol
and missing names that are used in the text below. and missing names that are used in the text below.
1.2. An Overview of Federation 1.2. An Overview of Federation
skipping to change at page 7, line 18 skipping to change at page 7, line 19
`----------' '---------' `----------' '---------'
< <
\ \
\ Authentication \ Authentication
\ \
\ \
\ \
\ \
\ +---------+ \ +---------+
\ | | O \ | | O
v| Client | \|/ Subject v| Client | \|/ Principal
| | | | | |
+---------+ / \ +---------+ / \
Figure 1: Entities and their Relationships Figure 1: Entities and their Relationships
A federation agreement typically encompasses operational A federation agreement typically encompasses operational
specifications and legal rules: specifications and legal rules:
Operational Specifications: Operational Specifications:
These includes the technical specifications (e.g. protocols used These includes the technical specifications (e.g. protocols used
to communicate between the three parties), process standards, to communicate between the three parties), process standards,
policies, identity proofing, credential and authentication policies, identity proofing, credential and authentication
algorithm requirements, performance requirements, assessment and algorithm requirements, performance requirements, assessment and
audit criteria, etc. The goal of these specifications to make the audit criteria, etc. The goal of operational specifications is to
system work and to accomplish interoperability. provide enough definition that the system works and
interoperability is possible.
Legal Rules: Legal Rules:
The legal rules take existing laws into consideration and provide The legal rules takes the legal framework into consideration and
contractual obligations to provide further clarification and provides contractual obligations for each entity, defines the
define responsibilities. These legal rules regulate the responsibilities and provides further clarification of the
operational specifications. These legal rules regulate the
operational specifications, make operational specifications operational specifications, make operational specifications
legally binding to the participants, define and govern the rights legally binding to the participants, define and govern the rights
and responsibilities of the participants. These legal rules may, and responsibilities of the participants. The legal rules may,
for example, describe liability for losses, termination rights, for example, describe liability for losses, termination rights,
enforcement mechanisms, measures of damage, dispute resolution, enforcement mechanisms, measures of damage, dispute resolution,
warranties, etc. warranties, etc.
The nature of federation dictates that there is some form of The nature of federation dictates that there is some form of
relationship between the identity provider and the relying party. relationship between the identity provider and the relying party.
This is particularly important when the relying party wants to use This is particularly important when the relying party wants to use
information obtained from the identity provider for access management information obtained from the identity provider for access management
decisions and when the identity provider does not want to release decisions and when the identity provider does not want to release
information to every relying party (or only under certain information to every relying party (or only under certain
conditions). conditions).
While it is possible to have a bilateral agreement between every IdP While it is possible to have a bilateral agreement between every IdP
and every RP; on an Internet scale this setup requires the and every RP; on an Internet scale this setup requires the
introduction of the multi-lateral federation concept, as the introduction of the multi-lateral federation concept, as the
management of such pair-wise relationships would otherwise prove management of such pair-wise relationships would otherwise prove
burdensome. burdensome.
While many of the non-technical aspects of federation, such as While many of the non-technical aspects of federation, such as
business practices and legal arrangements, are outside the scope of business practices and legal arrangements, are outside the scope of
the IETF they still impact the architectural setup on how to ensure the IETF, they still impact the architectural setup on how to ensure
the dynamic establishment of trust. the dynamic establishment of trust.
Some deployments demand the deployment of sophisticated technical Some deployments demand the deployment of sophisticated technical
infrastructure, including message routing intermediaries, to offer infrastructure, including message routing intermediaries, to offer
the required technical functionality. In other deployments fewer the required technical functionality. In other deployments fewer
technical components are needed. technical components are needed.
Figure 1 also shows the relationship between the IdP and the Subject. Figure 1 also shows the relationship between the IdP and the Subject.
Often a real world entity is associated with the Subject; for Often a real world entity is associated with the Subject; for
example, a person or some software. example, a person or some software.
The IdP will typically have a long-term relationship with the The IdP will typically have a long-term relationship with the
Subject. This relationship would typically involve the IdP Subject. This relationship would typically involve the IdP
positively identifying and credentialling the Subject (for example, positively identifying and credentialing the Subject (for example, at
at time of enrollment in the context of employment within an time of enrollment in the context of employment within an
organisation). The relationship will often be instantiated within an organisation). The relationship will often be instantiated within an
agreement between the IdP and the Subject (for example, within an agreement between the IdP and the Subject (for example, within an
employment contract or terms of use that stipulates the appropriate employment contract or terms of use that stipulates the appropriate
use of credentials and so forth). use of credentials and so forth).
While federation is often discussed within the context of relatively While federation is often discussed within the context of formal
formal relationships, such as between an enterprise and an employee relationships, such as between an enterprise and an employee or a
or a government and a citizen, federation does not in any way require government and a citizen, federation does not in require any
this; nor, indeed, does it require any particular level of formality. particular level of formality. For an IdP and a subject, it is
It is, for example, entirely compatible with a relationship between entirely compatible with a relationship between the IdP and Subject
the IdP and Subject that is only as weak as completing a web form and that is only Requiems completing a web form and confirming the
confirming the verification email. verification email. For an IdP and an RP, it is entirely compatible
with the IdP publishing a usage point and the RP using that data.
However, the nature and quality of the relationship between the However, the nature and quality of the relationship between the
Subject and the IdP is an important contributor to the level of trust Subject and the IdP is an important contributor to the level of trust
that an RP may attribute to an assertion describing a Subject made by that an RP may attribute to an assertion describing a Subject made by
an IdP. This is sometimes described as the Level of Assurance. an IdP. This is sometimes described as the Level of Assurance.
Similarly it is also important to note that, in the general case, Federation does not imposes requirement of an a priori relationship
there is no requirement of a long-term relationship between the RP or a long-term relationship between the RP and the Subject. This is
and the Subject. This is a property of federation that yields many a property of federation that yields many of its benefits. However,
of its benefits. However, federation does not preclude the federation does not preclude the possibility of a pre-existing
possibility of a pre-existing relationship existing between the RP relationship existing between the RP and the Subject, nor that they
and the Subject, nor that they may use the introduction to create a may use the introduction to create a new long-term relationship
new long-term relationship independent of the federation. independent of the federation.
Finally, it is important to reiterate that in some scenarios there Finally, it is important to reiterate that in some scenarios there
might indeed be a human behind the device denoted as Client and in might indeed be a human behind the device denoted as Client and in
other cases there is no human involved in the actual protocol other cases there is no human involved in the actual protocol
execution. execution.
1.3. Challenges to Contemporary Federation 1.3. Challenges to Contemporary Federation
As the number of federated services has proliferated, the role of the As the number of federated services has proliferated, the role of the
individual can become ambiguous in certain circumstances. For individual can become ambiguous in certain circumstances. For
example, a school might provide online access for a student's grades example, a school might provide online access for a student's grades
to their parents for review, and to the student's teacher for to their parents for review, and to the student's teacher for
modifying the grades. A teacher who is also a parent must clearly modification. A teacher who is also a parent must clearly
distinguish here role upon access. distinguish her role upon access.
Similarly, as the number of federations proliferates, it becomes Similarly, as the number of federations proliferates, it becomes
increasingly difficult to discover which identity provider(s) a user increasingly difficult to discover which identity provider(s) a user
is associated with. This is true for both the web and non-web case, is associated with. This is true for both the web and non-web case,
but is particularly acute for the latter as many non-web but is particularly acute for the latter as many non-web
authentication systems are not semantically rich enough on their own authentication systems are not semantically rich enough on their own
to allow for such ambiguities. For instance, in the case of an email to allow for such ambiguities. For instance, in the case of an email
provider, the use of SMTP and IMAP protocols does not on its own provider, the use of SMTP and IMAP protocols does not on its own
provide for a way to select a federation. However, the building provide for a way to select a federation. However, the building
blocks do exist to add this functionality. blocks do exist to add this functionality.
skipping to change at page 10, line 11 skipping to change at page 10, line 17
3. Client Application provides the NAI to RP: The client 3. Client Application provides the NAI to RP: The client
application setups a transport to the RP and begins the GSS-EAP application setups a transport to the RP and begins the GSS-EAP
authentication. The RP initiates the EAP protocol to the client authentication. The RP initiates the EAP protocol to the client
application, and the client provides the NAI to the RP in the application, and the client provides the NAI to the RP in the
form of the EAP response. form of the EAP response.
4. Discovery of federated IdP: The RP uses pre-configured 4. Discovery of federated IdP: The RP uses pre-configured
information or a federation proxy to determine what IdP to use information or a federation proxy to determine what IdP to use
based on policy and the provided NAI. This is discussed in based on policy and the provided NAI. This is discussed in
detail below. detail below (Section 2.1.2).
5. Request from Relying Party to IdP: Once the RP knows who the IdP 5. Request from Relying Party to IdP: Once the RP knows who the IdP
is, it (or its agent) will send a RADIUS/Diameter request to the is, it (or its agent) will send a RADIUS/Diameter request to the
IdP. The RADIUS/Diameter access request encapsulates the EAP IdP. The RADIUS/Diameter access request encapsulates the EAP
response. At this stage, the RP will likely have no idea who response. At this stage, the RP will likely have no idea who
the principal is. The RP claims its identity to the IdP in AAA the client is. The RP claims its identity to the IdP in AAA
attributes, and it may contain a SAML Attribute Requests in a attributes, and it may contain a SAML Attribute Requests in a
AAA attribute. AAA attribute.
6. IdP informs the principal of which EAP method to use: The 6. IdP informs the client of which EAP method to use: The available
available and appropriate methods are discussed below in this and appropriate methods are discussed below in this
memo. memo.[anchor4]
7. The EAP protocol is run: A bunch of EAP messages are passed 7. The EAP protocol is run: A bunch of EAP messages are passed
between the EAP peer and the EAP server, i.e., the principal and between the EAP peer and the EAP server, i.e., the client and
the IdP in our identity management terminology, until the result the IdP in our identity management terminology, until the result
of the authentication protocol is determined. The number and of the authentication protocol is determined. The number and
content of those messages will depend on the EAP method. If the content of those messages will depend on the EAP method. If the
IdP is unable to authenticate the principal, the process IdP is unable to authenticate the client, the process concludes
concludes here. As part of the EAP protocol, the principal will here. As part of the EAP protocol, the client will create a
create a channel bindings message to the IdP identifying, among channel bindings message to the IdP identifying, among other
other things, the RP to which it is attempting to authenticate. things, the RP to which it is attempting to authenticate. The
The IdP checks the channel binding data from the principal with IdP checks the channel binding data from the client with that
that provided by the RP via the AAA protocol. If the bindings provided by the RP via the AAA protocol. If the bindings do not
do not match the IdP fails the EAP protocol. match the IdP fails the EAP protocol.
8. Successful Authentication: The IdP (its EAP server) and EAP peer 8. Successful Authentication: The IdP (its EAP server) and EAP peer
/ subject have mutually authenticated each other. As a result / subject have mutually authenticated each other. As a result
of this step, the subject and the IdP hold two cryptographic of this step, the subject and the IdP hold two cryptographic
keys- a Master Session Key (MSK), and an Extended MSK (EMSK). keys- a Master Session Key (MSK), and an Extended MSK (EMSK).
There is some confidence that the RP is the one the principal is There is some confidence that the RP is the one the client is
communicating with as the channel binding data validated. This communicating with as the channel binding data validated. This
allows for a claim of authentication for the RP to the allows for a claim of authentication for the RP to the client.
principal.
9. Local IdP Policy Check: At this stage, the IdP checks local 9. Local IdP Policy Check: At this stage, the IdP checks local
policy to determine whether the RP and subject are authorized policy to determine whether the RP and subject are authorized
for a given transaction/service, and if so, what if any, for a given transaction/service, and if so, what if any,
attributes will be released to the RP. The RP will have done attributes will be released to the RP. The RP will have done
it's policy checks during the discovery process. its policy checks during the discovery process.
10. Response from the IdP to the Relying Party: Once the IdP has 10. Response from the IdP to the Relying Party: Once the IdP has
made a determination of whether and how to authenticate and made a determination of whether and how to authenticate and
authorize the principal to the RP, it returns either a negative authorize the client to the RP, it returns either a negative AAA
AAA result to the RP, or it returns a positive result to the RP, result to the RP, or it returns a positive result to the RP,
along with an optional set of AAA attributes associated with the along with an optional set of AAA attributes associated with the
principal that could include one or more SAML assertions. In client (usually as one or more SAML assertions). In addition,
addition, an EAP MSK is returned to the RP. an EAP MSK is returned to the RP.
11. RP Processes Results: When the RP receives the result from the 11. RP Processes Results: When the RP receives the result from the
IdP, it should have enough information to either grant or refuse IdP, it should have enough information to either grant or refuse
a resource access request. It may have information that a resource access request. It may have information that
associates the principal with specific authorization identities. associates the client with specific authorization identities.
If additional attributes are needed from the IdP the RP may make If additional attributes are needed from the IdP the RP may make
a new SAML Request to the IdP. It will apply these results in a new SAML Request to the IdP. It will apply these results in
an application-specific way. an application-specific way.
12. RP returns results to principal: Once the RP has a response it 12. RP returns results to client: Once the RP has a response it must
must inform the client application of the result. If all has inform the client application of the result. If all has gone
gone well, all are authenticated, and the application proceeds well, all are authenticated, and the application proceeds with
with appropriate authorization levels. appropriate authorization levels.
An example communication flow is given below: An example communication flow is given below:
Relying Client Identity Relying Client Identity
Party App Provider Party App Provider
| (1) | Client App gets NAI (somehow) | (1) | Client App gets NAI (somehow)
| | | | | |
|<-----(2)----->| | Mechanism Selection |<-----(2)----->| | Mechanism Selection
| | | | | |
|<-----(3)-----<| | NAI transmitted to RP |<-----(3)-----<| | NAI transmitted to RP
| | | | | |
|<=====(4)====================>| Discovery |<=====(4)====================>| Discovery
| | | | | |
|>=====(5)====================>| Access request from RP to IdP |>=====(5)====================>| Access request from RP to IdP
| | | | | |
| |< - - (6) - -<| EAP method to Principal | |< - - (6) - -<| EAP method to Client
| | | | | |
| |< - - (7) - ->| EAP Exchange to authenticate | |< - - (7) - ->| EAP Exchange to authenticate
| | | Principal | | | Client
| | | | | |
| | (8 & 9) Local Policy Check | | (8 & 9) Local Policy Check
| | | | | |
|<====(10)====================<| IdP Assertion to RP |<====(10)====================<| IdP Assertion to RP
| | | | | |
| | (11) RP processes results (11) | | RP processes results
| | | | | |
|>----(12)----->| | Results to client app. |>----(12)----->| | Results to client app.
----- = Between Client App and RP ----- = Between Client App and RP
===== = Between RP and IdP ===== = Between RP and IdP
- - - = Between Client App and IdP - - - = Between Client App and IdP
1.5. Design Goals 1.5. Design Goals
Our key design goals are as follows: Our key design goals are as follows:
o Each party of a transaction will be authenticated, and the o Each party of a transaction will be authenticated, and the client
principal will be authorized for access to a specific resource . will be authorized for access to a specific resource.
o Means of authentication is decoupled so as to allow for multiple o Means of authentication is decoupled so as to allow for multiple
authentication methods. authentication methods.
o Hence, the architecture requires no sharing of long term private o Hence, the architecture requires no sharing of long term private
keys. keys.
o The system will scale to large numbers of identity providers, o The system will scale to large numbers of identity providers,
relying parties, and users. relying parties, and users.
o The system will be designed primarily for non-Web-based o The system will be designed primarily for non-Web-based
authentication. authentication.
o The system will build upon existing standards, components, and o The system will build upon existing standards, components, and
operational practices. operational practices.
Designing new three party authentication and authorization protocols Designing new three party authentication and authorization protocols
is hard and frought with risk of cryptographic flaws. Achieving is hard and fraught with risk of cryptographic flaws. Achieving
widespead deployment is even more difficult. A lot of attention on widespead deployment is even more difficult. A lot of attention on
federated access has been devoted to the Web. This document instead federated access has been devoted to the Web. This document instead
focuses on a non-Web-based environment and focuses on those protocols focuses on a non-Web-based environment and focuses on those protocols
where HTTP is not used. Despite the increased excitement for where HTTP is not used. Despite the increased excitement for
layering every protocol on top of HTTP there are still a number of layering every protocol on top of HTTP there are still a number of
protocols available that do not use HTTP-based transports. Many of protocols available that do not use HTTP-based transports. Many of
these protocols are lacking a native authentication and authorization these protocols are lacking a native authentication and authorization
framework of the style shown in Figure 1. framework of the style shown in Figure 1.
1.6. Client to Relying Party Transport 1.6. Use of AAA
The transport of data between the client and the relying part is not
provided by GSS-API. GSS-API creates and consumes messages, but it
does not provide the transport itself, instead the protocol using
GSS-API needs to provide the transport. In many cases HTTP or HTTPS
is used for this transport, but other transports are perfectly
acceptable. The core GSS-API document [RFC2743] provides some
details on what requirements exist.
In addition we highlight the following:
o The transport does not need to provide either privacy or
integrity. After GSS-EAP has finished negotiation, GSS-API can be
used to provide both services. If the negotiation process itself
needs protection from eavesdroppers then the transport would need
to provide the necessary services.
o The transport needs to provide reliable transport of the messages.
o The transport needs to ensure that tokens are delivered in order
during the negotiation process.
o GSS-API messages need to be delivered atomically. If the
transport breaks up a message it must also reassemble the message
before delivery.
1.7. Use of AAA
Interestingly, for network access authentication the usage of the AAA Interestingly, for network access authentication the usage of the AAA
framework with RADIUS [RFC2865] and Diameter [RFC3588] was quite framework with RADIUS [RFC2865] and Diameter [RFC3588] was quite
successful from a deployment point of view. To map the terminology successful from a deployment point of view. To map the terminology
used in Figure 1 to the AAA framework the IdP corresponds to the AAA used in Figure 1 to the AAA framework the IdP corresponds to the AAA
server, the RP corresponds to the AAA client, and the technical server, the RP corresponds to the AAA client, and the technical
building blocks of a federation are AAA proxies, relays and redirect building blocks of a federation are AAA proxies, relays and redirect
agents (particularly if they are operated by third parties, such as agents (particularly if they are operated by third parties, such as
AAA brokers and clearing houses). The front-end, i.e. the end host AAA brokers and clearing houses). The front-end, i.e. the end host
to AAA client communication, is in case of network access to AAA client communication, is in case of network access
authentication offered by link layer protocols that forward authentication offered by link layer protocols that forward
authentication protocol exchanges back-and-forth. An example of a authentication protocol exchanges back-and-forth. An example of a
large scale RADIUS-based federation is EDUROAM [2]. large scale RADIUS-based federation is EDUROAM [2].
Is it possible to design a system that builds on top of successful By using the AAA framework, ABFAB gets a lot of mileage as many of
protocols to offer non-Web-based protocols with a solid starting the federation agreements already exist and merely need to be
point for authentication and authorization in a distributed system? expanded to cover the ABFAB additions. The AAA framework has already
addressed some of the problems outlined above. For example,
o It already needs a method of doing routing of requests based on a
domain.
o It already has an extensible architecture allowing for new
attributes to be defined and transported.
o Pre-existing relationships can be re-used.
1.7. Use of GSS-API
Expand here
2. Architecture 2. Architecture
Section 1 already introduced the federated access architecture, with We have already introduced the federated access architecture, with
the illustration of the different actors that need to interact, but the illustration of the different actors that need to interact, but
it did not expand on the specifics of providing support for non-Web did not expand on the specifics of providing support for non-Web
based applications. This section details this aspect and motivates based applications. This section details this aspect and motivates
design decisions. The main theme of the work described in this design decisions. The main theme of the work described in this
document is focused on re-using existing building blocks that have document is focused on re-using existing building blocks that have
been deployed already and to re-arrange them in a novel way. been deployed already and to re-arrange them in a novel way.
Although this architecture assumes updates to both the relying party Although this architecture assumes updates to the relying party, the
as well as to the client for application integration, those changes client application and the Identity Provider, those changes are kept
are kept at a minimum. A mechanism that can demonstrate deployment at a minimum. A mechanism that can demonstrate deployment benefits
benefits (based on ease of update of existing software, low (based on ease of update of existing software, low implementation
implementation effort, etc.) is preferred and there may be a need to effort, etc.) is preferred and there may be a need to specify
specify multiple mechanisms to support the range of different multiple mechanisms to support the range of different deployment
deployment scenarios. scenarios.
There are a number of ways for encapsulating EAP into an application There are a number of ways for encapsulating EAP into an application
protocol. For ease of integration with a wide range of non-Web based protocol. For ease of integration with a wide range of non-Web based
application protocols the usage of the GSS-API was chosen. application protocols the usage of the GSS-API was chosen.
Encapsulating EAP into the GSS-API also allows EAP to be used in Encapsulating EAP into the GSS-API also allows EAP to be used in
SASL. A description of the technical specification can be found in SASL. A description of the technical specification can be found in
[I-D.ietf-abfab-gss-eap]. Other alternatives exist as well and may [I-D.ietf-abfab-gss-eap]. Other alternatives exist as well and may
be considered later, such as "TLS using EAP Authentication" be considered later, such as "TLS using EAP Authentication"
[I-D.nir-tls-eap]. [I-D.nir-tls-eap].[anchor9]
The architecture consists of several buiding blocks, which is shown The architecture consists of several building blocks, which is shown
graphically in Figure 2. The subsections below explain relationship graphically in Figure 2. In the following sections, we discuss the
of the protocol components in more detail. data flow between each of the entities, the protocols used for that
data flow and some of the trade-offs made in choosing the protocols.
+--------------+ +--------------+
| Identity | | Identity |
| Provider | | Provider |
| (IdP) | | (IdP) |
+-^----------^-+ +-^----------^-+
* EAP o RADIUS/ * EAP o RADIUS/
* o Diameter * o Diameter
--v----------v-- --v----------v--
/// \\\ /// \\\
skipping to change at page 16, line 44 skipping to change at page 16, line 44
<****>: Client-to-IdP Exchange <****>: Client-to-IdP Exchange
<---->: Client-to-RP Exchange <---->: Client-to-RP Exchange
<oooo>: RP-to-IdP Exchange <oooo>: RP-to-IdP Exchange
<====>: Protocol through which GSS-API/GS2 exchanges are tunnelled <====>: Protocol through which GSS-API/GS2 exchanges are tunnelled
Figure 2: ABFAB Protocol Instantiation Figure 2: ABFAB Protocol Instantiation
2.1. Relying Party to Identity Provider 2.1. Relying Party to Identity Provider
The federation substrate is responsible for the communication between Communications between the Relying Part and the Identity Provider is
the relying party and the identity provider. This layer is done by the federation substrate. This communication channel is
responsible for the inter-domain communication and for the technical responsible for:
mechanisms necessary to establish inter-domain trust.
A key design goal is the re-use of an existing infrastructure, we o Establishing the trust relationship between the RP and the IdP.
build upon the AAA framework as utilized by RADIUS [RFC2138] and
Diameter [RFC3588]. Since this document does not aim to re-describe
the AAA framework the interested reader is referred to [RFC2904].
Building on the AAA infrastructure, and RADIUS and Diameter as o Determining the Rules governing the relationship.
protocols, modifications to that infrastructure is to be avoided.
Also, modifications to AAA servers should be kept at a minimum. o Conveying packets between the RP and IdP.
o Providing the means of establishing a trust relationship between
the RP and the client.
The ABFAB working group has chosen the AAA framework for the messages
transported between the RP and IdP. This allows for the standard AAA
framework to be used to establish the trust relationship between the
RP and the IdP while allowing other newer routing mechanisms using
the same message format to be used in the future. The ABFAB protocol
itself details the method of establishing the trust relationship
between the RP and the client.
2.1.1. AAA, RADIUS and Diameter
The IETF has defined a federation framework already with the
Authentication, Authorization and Accounting (AAA) framework
[RFC2903], [RFC2904]. Two implementations of the AAA framework exist
in RADIUS [RFC2138] and Diameter [RFC3588] protocols. The existence
of these protocols allows us to re-use a pair of existing protocols
that have been widely deployed and are reasonable well understood.
These protocols are nicely designed so that they can carry additional
attributes with minimal changes to either the protocol or existing
AAA servers.
The astute reader will notice that RADIUS and Diameter have The astute reader will notice that RADIUS and Diameter have
substantially similar characteristics. Why not pick one? A key substantially similar characteristics. Why not pick one? A key
difference is that today RADIUS is largely transported upon UDP, and difference is that today RADIUS is largely transported upon UDP, and
its use is largely, though not exclusively, intra-domain. Diameter its use is largely, though not exclusively, intra-domain. Diameter
itself was designed to scale to broader uses. We leave as a itself was designed to scale to broader uses. We leave as a
deployment decision, which protocol will be appropriate. deployment decision, which protocol will be appropriate. The
protocol defines all the necessary new AAA attributes as RADIUS
attributes, this allows for the same structures and attributes to be
used in both RADIUS and Diameter. We also note that there exist
proxies which convert from RADIUS to Diameter and back. This makes
it possible for both to be deployed in a single federation substrate.
Through the integrity protection mechanisms in the AAA framework, the Through the integrity protection mechanisms in the AAA framework, the
relying party can establish technical trust that messages are being identity provider can establish technical trust that messages are
sent by the appropriate relying party. Any given interaction will be being sent by the appropriate relying party. Any given interaction
associated with one federation at the policy level. The legal or will be associated with one federation at the policy level. The
business relationship defines what statements the identity provider legal or business relationship defines what statements the identity
is trusted to make and how these statements are interpreted by the provider is trusted to make and how these statements are interpreted
relying party. The AAA framework also permits the relying party or by the relying party. The AAA framework also permits the relying
elements between the relying party and identity provider to make party or elements between the relying party and identity provider to
statements about the relying party. make statements about the relying party.
The AAA framework provides transport for attributes. Statements made The AAA framework provides transport for attributes. Statements made
about the subject by the identity provider, statements made about the about the subject by the identity provider, statements made about the
relying party and other information is transported as attributes. relying party and other information are transported as attributes.
One demand that the AAA substrate makes of the upper layers is that One demand that the AAA substrate makes of the upper layers is that
they must properly identify the end points of the communication. It they must properly identify the end points of the communication. It
must be possible for the AAA client at the RP to determine where to must be possible for the AAA client at the RP to determine where to
send each RADIUS or Diameter message. Without this requirement, it send each RADIUS or Diameter message. Without this requirement, it
would be the RP's responsibility to determine the identity of the would be the RP's responsibility to determine the identity of the
principal on its own, without the assistance of an IdP. This client on its own, without the assistance of an IdP. This
architecture makes use of the Network Access Identifier (NAI), where architecture makes use of the Network Access Identifier (NAI), where
the IdP is indicated in the realm component [RFC4282]. The NAI is the IdP is indicated by the realm component [RFC4282]. The NAI is
represented and consumed by the GSS-API layer as GSS_C_NT_USER_NAME represented and consumed by the GSS-API layer as GSS_C_NT_USER_NAME
as specified in [RFC2743]. The GSS-API EAP mechanism includes the as specified in [RFC2743]. The GSS-API EAP mechanism includes the
NAI in the EAP Response/Identity message. NAI in the EAP Response/Identity message.
2.1.2. Discovery and Rules Determination
While we are using the AAA protocols to communicate with the IdP, the
RP may have multiple federation substrates to select from. The RP
has a number of criteria that it will use in selecting which of the
different federations to use:
o The federation selected must be able to communicate with the IdP.
o The federation selected must match the business rules and
technical policies required for the RP security requirements.
The RP needs to discover which federation will be used to contact the The RP needs to discover which federation will be used to contact the
IDP. As part of this process, the RP determines the set of business IdP. The first selection criteria in discovery is going to be the
rules and technical policies governing the relationship; this is name of the IdP to be contacted. The second selection criteria in
called rules determination. The RP also needs to establish technical discovery is going to be the set of business rules and technical
trust in the communications with the IDP. policies governing the relationship; this is called rules
determination. The RP also needs to establish technical trust in the
communications with the IdP.
Rules determination covers a broad range of decisions about the Rules determination covers a broad range of decisions about the
exchange. One of these is whether the given RP is permitted to talk exchange. One of these is whether the given RP is permitted to talk
to the IDP using a given federation at all, so rules determination to the IdP using a given federation at all, so rules determination
encompasses the basic authorization decision. Other factors are encompasses the basic authorization decision. Other factors are
included, such as what policies govern release of information about included, such as what policies govern release of information about
the principal to the RP and what policies govern the RP's use of this the principal to the RP and what policies govern the RP's use of this
information. While rules determination is ultimately a business information. While rules determination is ultimately a business
function, it has significant impact on the technical exchanges. The function, it has significant impact on the technical exchanges. The
protocols need to communicate the result of authorization. When protocols need to communicate the result of authorization. When
multiple sets of rules are possible, the protocol must disambiguate multiple sets of rules are possible, the protocol must disambiguate
which set of rules are in play. Some rules have technical which set of rules are in play. Some rules have technical
enforcement mechanisms; for example in some federations intermediates enforcement mechanisms; for example in some federations intermediates
validate information that is being communicated within the validate information that is being communicated within the
federation. federation.
Several deployment approaches are possible. These can most easily be ABFAB has not formally defined any part of discovery at this point.
The process of specifying and evaluating the business rules and
technical policies is too complex to provide a simple framework.
There is not currently a way to know if a AAA proxy is able to
communicate with a specific IdP, although this may change with some
of the routing protocols that are being considered. At the present
time, the discovery process is going to be a manual configuration
process.
2.1.3. Routing and Technical Trust
Several approaches to having messages routed through the federation
substrate are possible. These routing methods can most easily be
classified based on the mechanism for technical trust that is used. classified based on the mechanism for technical trust that is used.
The choice of technical trust mechanism constrains how rules The choice of technical trust mechanism constrains how rules
determination is implemented. Regardless of what deployment strategy determination is implemented. Regardless of what deployment strategy
is chosen, it is important that the technical trust mechanism is chosen, it is important that the technical trust mechanism
constrain the names of both parties to the exchange. The trust constrain the names of both parties to the exchange. The trust
mechanism ought to ensure that the entity acting as IDP for a given mechanism ought to ensure that the entity acting as IdP for a given
NAI is permitted to be the IDP for that realm, and that any service NAI is permitted to be the IdP for that realm, and that any service
name claimed by the RP is permitted to be claimed by that entity. name claimed by the RP is permitted to be claimed by that entity.
Here are the categories of technical trust determination: Here are the categories of technical trust determination:
AAA Proxy: The simplest model is that an RP supports a request AAA Proxy:
directly to an AAA proxy. The hop-by-hop integrity protection of The simplest model is that an RP supports a request directly to an
the AAA fabric provides technical trust. An RP can submit a AAA proxy. The hop-by-hop integrity protection of the AAA fabric
request directly to a federation. Alternatively, a federation provides technical trust. An RP can submit a request directly to
disambiguation fabric can be used. Such a fabric takes a federation. Alternatively, a federation disambiguation fabric
information about what federations the RP is part of and what can be used. Such a fabric takes information about what
federations the IDP is part of and routes a message to the federations the RP is part of and what federations the IdP is part
appropriate federation. The routing of messages across the fabric of and routes a message to the appropriate federation. The
plus attributes added to requests and responses provides rules routing of messages across the fabric plus attributes added to
determination. For example, when a disambiguation fabric routes a requests and responses provides rules determination. For example,
message to a given federation, that federation's rules are chosen. when a disambiguation fabric routes a message to a given
Naming is enforced as messages travel across the fabric. The federation, that federation's rules are chosen. Naming is
entities near the RP confirm its identity and validate names it enforced as messages travel across the fabric. The entities near
claims. The fabric routes the message towards the appropriate the RP confirm its identity and validate names it claims. The
IDP, validating the IDP's name in the process. The routing can be fabric routes the message towards the appropriate IdP, validating
statically configured. Alternatively a routing protocol could be the IdP's name in the process. The routing can be statically
developed to exchange reachability information about given IDPs configured. Alternatively a routing protocol could be developed
and to apply policy across the AAA fabric. Such a routing to exchange reachability information about given IdPs and to apply
protocol could flood naming constraints to the appropriate points policy across the AAA fabric. Such a routing protocol could flood
in the fabric. naming constraints to the appropriate points in the fabric.
Trust Broker: Instead of routing messages through AAA proxies, some Trust Broker:
trust broker could establish keys between entities near the RP and Instead of routing messages through AAA proxies, some trust broker
entities near the IDP. The advantage of this approach is could establish keys between entities near the RP and entities
efficiency of message handling. Fewer entities are needed to be near the IdP. The advantage of this approach is efficiency of
involved for each message. Security may be improved by sending message handling. Fewer entities are needed to be involved for
individual messages over fewer hops. Rules determination involves each message. Security may be improved by sending individual
decisions made by trust brokers about what keys to grant. Also, messages over fewer hops. Rules determination involves decisions
associated with each credential is context about rules and about made by trust brokers about what keys to grant. Also, associated
other aspects of technical trust including names that may be with each credential is context about rules and about other
claimed. A routing protocol similar to the one for AAA proxies is aspects of technical trust including names that may be claimed. A
likely to be useful to trust brokers in flooding rules and naming routing protocol similar to the one for AAA proxies is likely to
be useful to trust brokers in flooding rules and naming
constraints. constraints.
Global Credential: A global credential such as a public key and Global Credential:
certificate in a public key infrastructure can be used to A global credential such as a public key and certificate in a
establish technical trust. A directory or distributed database public key infrastructure can be used to establish technical
such as the Domain Name System is needed for an RP to discover trust. A directory or distributed database such as the Domain
what endpoint to contact for a given NAI. Certificates provide a Name System is used by the RP to discover the endpoint to contact
place to store information about rules determination and naming for a given NAI. Either the database or certificates can provide
constraints. Provided that no intermediates are required and that a place to store information about rules determination and naming
the RP and IDP are sufficient to enforce and determine rules, constraints. Provided that no intermediates are required (or
rules determination is reasonably simple. However applying appear to be required) and that the RP and IdP are sufficient to
certain rules is likely to be quite complex. For example if enforce and determine rules, rules determination is reasonably
multiple sets of rules are possible between an IDP and RP, simple. However applying certain rules is likely to be quite
confirming the correct set is used may be difficult. This is complex. For example if multiple sets of rules are possible
particularly true if intermediates are involved in making the between an IdP and RP, confirming the correct set is used may be
decision. Also, to the extent that directory information needs to difficult. This is particularly true if intermediates are
be trusted, rules determination may be more complex. involved in making the decision. Also, to the extent that
directory information needs to be trusted, rules determination may
be more complex.
Real-world deployments are likely to be mixtures of these basic Real-world deployments are likely to be mixtures of these basic
approaches. For example, it will be quite common for an RP to route approaches. For example, it will be quite common for an RP to route
traffic to a AAA proxy within an organization. That proxy MAY use traffic to a AAA proxy within an organization. That proxy could then
any of the three methods to get closer to the IDP. It is also likely use any of the three methods to get closer to the IdP. It is also
that rather than being directly reachable, an IDP may have a proxy likely that rather than being directly reachable, the IdP may have a
within its organization. Federations MAY provide a traditional AAA proxy on the edge of its organization. Federations will likely
proxy interface even if they also provide another mechanism for provide a traditional AAA proxy interface even if they also provide
increased efficiency or security. another mechanism for increased efficiency or security.
2.1.4. SAML Assertions
For the traditional use of AAA frameworks, network access, the only
requirement that was necessary to grant access was an affirmative
response from the IdP. In the ABFAB world, the RP may need to get
additional information about the client before granting access.
ABFAB therefore has a requirement that it can transport an arbitrary
set of attributes about the client from the IdP to the RP.
Security Assertions Markup Language (SAML) [OASIS.saml-core-2.0-os]
was designed in order to carry an extensible set of attributes about
a subject. Since SAML is extensible in the attribute space, ABFAB
has no immediate needs to update the core SAML specifications for our
work. It will be necessary to update IdPs that need to return SAML
assertions to IdPs and for both the IdP and the RP to implement a new
SAML profile designed to carry SAML assertions in AAA. The new
profile can be found in RFCXXXX [I-D.ietf-abfab-aaa-saml].
There are two issues that need to be highlighted:
o The security of SAML Assertions.
o Namespaces and mapping of SAML attributes.
SAML Assertions have an optional signature that can be used to
protect and provide origination of the assertion. These signatures
are normally based on asymmetric key operations and require that the
verifier be able to check not only the cryptographic operation, but
also the binding of the originators name and the public key. In a
federated environment it will not always be possible for the RP to
validate the binding, for this reason the technical trust established
in the federation is used as an alternate method of validating the
origination and integrity of the SAML Assertion.
Attributes placed in SAML Assertions can have different namespaces
assigned to the same name. In many, but not all, cases a the
federation agreements will determine what attributes can be used in a
SAML statement. This means that the RP needs to map from the
federation names, types and semantics into the onces that the
policies of the RP are written in. In other cases the federation
substrate may modify the SAML Assertions in transit to do the
necessary namespace, naming and semantic mappings as the assertion
crosses the different boundaries in the federation. If the proxies
are modifying the SAML Assertion, then will obviously remove any
signatures on the SAML Assertions as they would no longer validate.
In this case the technical trust is the required mechanism for
validating the integrity of the assertion. In the last case, the
attributes may still be in the namespace of the originating IdP.
When this occurs the RP will need to get the required mapping
operations from the federation agreements and do the appropriate
mappings itself.
2.2. Client To Identity Provider 2.2. Client To Identity Provider
Looking at the communications between the client and the IdP, the
following items need to be dealt with:
o The client and the IdP need to mutually authenticate each other.
o The client and the IdP need to mutually agree on the identity of
the RP.
ABFAB selected EAP for the purposes of mutual authentication and
assisted in creating some new EAP channel binding documents for
dealing with determining the identity of the RP. ABFAB has defined
and specified a new channel binding mechanism that operates as an EAP
method for the purpose of agreeing on the identity of the RP.
2.2.1. Extensible Authentication Protocol (EAP)
Traditional web federation does not describe how a subject interacts Traditional web federation does not describe how a subject interacts
with an identity provider for authentication. As a result, this with an identity provider for authentication. As a result, this
communication is not standardized. There are several disadvantages communication is not standardized. There are several disadvantages
to this approach. It is difficult to have subjects that are machines to this approach. It is difficult to have subjects that are machines
rather than humans that use some sort of programatic credential. In rather than humans that use some sort of programatic credential. In
addition, use of browsers for authentication restricts the deployment addition, use of browsers for authentication restricts the deployment
of more secure forms of authentication beyond plaintext username and of more secure forms of authentication beyond plaintext username and
password known by the server. In a number of cases the password known by the server. In a number of cases the
authentication interface may be presented before the subject has authentication interface may be presented before the subject has
adequately validated they are talking to the intended server. By adequately validated they are talking to the intended server. By
skipping to change at page 20, line 35 skipping to change at page 23, line 18
and successfully deployed technology, namely by the Extensible and successfully deployed technology, namely by the Extensible
Authentication Protocol (EAP) framework [RFC3748]. Figure 2 Authentication Protocol (EAP) framework [RFC3748]. Figure 2
illustrates the integration graphically. illustrates the integration graphically.
EAP is an end-to-end framework; it provides for two-way communication EAP is an end-to-end framework; it provides for two-way communication
between a peer (i.e,service client or principal) through the between a peer (i.e,service client or principal) through the
authenticator (i.e., service provider) to the back-end (i.e., authenticator (i.e., service provider) to the back-end (i.e.,
identity provider). Conveniently, this is precisely the identity provider). Conveniently, this is precisely the
communication path that is needed for federated identity. Although communication path that is needed for federated identity. Although
EAP support is already integrated in AAA systems (see [RFC3579] and EAP support is already integrated in AAA systems (see [RFC3579] and
[RFC4072]) several challenges remain: one is to carry EAP payloads [RFC4072]) several challenges remain:
from the end host to the relying party. Another is to verify
statements the relying party has made to the subject, confirm these o The first is how to carry EAP payloads from the end host to the
statements are consistent with statements made to the identity relying party.
provider and confirm all the above are consistent with the federation
and any federation-specific policy or configuration. Another o Another is to verify statements the relying party has made to the
challenge is choosing which identity provider to use for which subject, confirm these statements are consistent with statements
service. made to the identity provider and confirm all the above are
consistent with the federation and any federation-specific policy
or configuration.
o Another challenge is choosing which identity provider to use for
which service.
2.2.2. Channel Binding
The client knows, in theory, the name of the RP that it attempted to
connect to, however in the event that an attacker has intercepted the
protocol, the client and the IdP need to be able to detect this
situation. A general overview of the problem can be found in
[I-D.hartman-emu-mutual-crypto-bind].
The recommended way to deal with channel binding can be found in RFC
XXXX [I-D.ietf-emu-chbind].
2.3. Client to Relying Party 2.3. Client to Relying Party
The final set of interactions between parties to consider are those
between the client and the RP. In some ways this is the most complex
set since at least part of it is outside the scope of the ABFAB work.
The interactions between these parties include:
o Running the protocol that implements the web service that is
provided by the RP and desired by the client.
o Authenticating the client to the RP and the RP to the client.
o Providing the necessary security services to the web service
protocol that it needs beyond authentication.
2.3.1. GSS-API
One of the remaining layers is responsible for integration of One of the remaining layers is responsible for integration of
federated authentication into the application. There are a number of federated authentication into the application. There are a number of
approaches that applications have adopted for security. So, there approaches that applications have adopted for security. So, there
may need to be multiple strategies for integration of federated may need to be multiple strategies for integration of federated
authentication into applications. However, we have started with a authentication into applications. However, we have started with a
strategy that provides integration to a large number of application strategy that provides integration to a large number of application
protocols. protocols.
Many applications such as SSH [RFC4462], NFS [RFC2203], DNS [RFC3645] Many applications such as SSH [RFC4462], NFS [RFC2203], DNS [RFC3645]
and several non-IETF applications support the Generic Security and several non-IETF applications support the Generic Security
skipping to change at page 23, line 5 skipping to change at page 25, line 23
integration. What does this mean from a protocol standpoint and how integration. What does this mean from a protocol standpoint and how
does this relate to other layers? This means we need to design a does this relate to other layers? This means we need to design a
concrete GSS-API mechanism. We have chosen to use a GSS-API concrete GSS-API mechanism. We have chosen to use a GSS-API
mechanism that encapsulates EAP authentication. So, GSS-API (and mechanism that encapsulates EAP authentication. So, GSS-API (and
SASL) encapsulate EAP between the end-host and the service. The AAA SASL) encapsulate EAP between the end-host and the service. The AAA
framework encapsulates EAP between the relying party and the identity framework encapsulates EAP between the relying party and the identity
provider. The GSS-API mechanism includes rules about how principals provider. The GSS-API mechanism includes rules about how principals
and services are named as well as per-message security and other and services are named as well as per-message security and other
facilities required by the applications we wish to support. facilities required by the applications we wish to support.
2.3.2. Protocol Transport
The transport of data between the client and the relying party is not
provided by GSS-API. GSS-API creates and consumes messages, but it
does not provide the transport itself, instead the protocol using
GSS-API needs to provide the transport. In many cases HTTP or HTTPS
is used for this transport, but other transports are perfectly
acceptable. The core GSS-API document [RFC2743] provides some
details on what requirements exist.
In addition we highlight the following:
o The transport does not need to provide either privacy or
integrity. After GSS-EAP has finished negotiation, GSS-API can be
used to provide both services. If the negotiation process itself
needs protection from eavesdroppers then the transport would need
to provide the necessary services.
o The transport needs to provide reliable transport of the messages.
o The transport needs to ensure that tokens are delivered in order
during the negotiation process.
o GSS-API messages need to be delivered atomically. If the
transport breaks up a message it must also reassemble the message
before delivery.
3. Application Security Services 3. Application Security Services
One of the key goals is to integrate federated authentication into One of the key goals is to integrate federated authentication into
existing application protocols and where possible, existing existing application protocols and where possible, existing
implementations of these protocols. Another goal is to perform this implementations of these protocols. Another goal is to perform this
integration while meeting the best security practices of the integration while meeting the best security practices of the
technologies used to perform the integration. This section describes technologies used to perform the integration. This section describes
security services and properties required by the EAP GSS-API security services and properties required by the EAP GSS-API
mechanism in order to meet these goals. This information could be mechanism in order to meet these goals. This information could be
viewed as specific to that mechanism. However, other future viewed as specific to that mechanism. However, other future
skipping to change at page 24, line 37 skipping to change at page 27, line 37
3.2. GSS-API Channel Binding 3.2. GSS-API Channel Binding
[RFC5056] defines a concept of channel binding to prevent man-in-the- [RFC5056] defines a concept of channel binding to prevent man-in-the-
middle attacks. It is common to provide SASL and GSS-API with middle attacks. It is common to provide SASL and GSS-API with
another layer to provide transport security; Transport Layer Security another layer to provide transport security; Transport Layer Security
(TLS) is the most common such layer. TLS provides its own server (TLS) is the most common such layer. TLS provides its own server
authentication. However there are a variety of situations where this authentication. However there are a variety of situations where this
authentication is not checked for policy or usability reasons. Even authentication is not checked for policy or usability reasons. Even
when it is checked, if the trust infrastructure behind the TLS when it is checked, if the trust infrastructure behind the TLS
authentication is different from the trust infrastructure behind the authentication is different from the trust infrastructure behind the
GSS-API mutual authentication. If the endpoints of the GSS-API GSS-API mutual authentication then confirming the end-points using
authentication are different than the endpoints of the lower layer, both trust infrastructures is likely to enhance security. If the
this is a strong indication of a problem such as a man-in-the-middle endpoints of the GSS-API authentication are different than the
attack. Channel binding provides a facility to determine whether endpoints of the lower layer, this is a strong indication of a
these endpoints are the same. problem such as a man-in-the-middle attack. Channel binding provides
a facility to determine whether these endpoints are the same.
The GSS-EAP mechanism needs to support channel binding. When an The GSS-EAP mechanism needs to support channel binding. When an
application provides channel binding data, the mechanism needs to application provides channel binding data, the mechanism needs to
confirm this is the same on both sides consistent with the GSS-API confirm this is the same on both sides consistent with the GSS-API
specification. XXXThere is an open question here as to the details; specification. XXXThere is an open question here as to the details;
today RFC 5554 governs. We could use that and the current draft today RFC 5554 governs. We could use that and the current draft
assumes we will. However in Beijing we became aware of some changes assumes we will. However in Beijing we became aware of some changes
to these details that would make life much better for GSS to these details that would make life much better for GSS
authentication of HTTP. We should resolve this with kitten and authentication of HTTP. We should resolve this with kitten and
replace this note with a reference to the spec we're actually replace this note with a reference to the spec we're actually
skipping to change at page 36, line 43 skipping to change at page 39, line 43
[I-D.iab-privacy-terminology] [I-D.iab-privacy-terminology]
Hansen, M., Tschofenig, H., Smith, R., and A. Cooper, Hansen, M., Tschofenig, H., Smith, R., and A. Cooper,
"Privacy Terminology and Concepts", "Privacy Terminology and Concepts",
draft-iab-privacy-terminology-01 (work in progress), draft-iab-privacy-terminology-01 (work in progress),
March 2012. March 2012.
[I-D.ietf-abfab-gss-eap] [I-D.ietf-abfab-gss-eap]
Hartman, S. and J. Howlett, "A GSS-API Mechanism for the Hartman, S. and J. Howlett, "A GSS-API Mechanism for the
Extensible Authentication Protocol", Extensible Authentication Protocol",
draft-ietf-abfab-gss-eap-07 (work in progress), May 2012. draft-ietf-abfab-gss-eap-08 (work in progress), June 2012.
[I-D.ietf-abfab-aaa-saml]
Howlett, J. and S. Hartman, "A RADIUS Attribute, Binding
and Profiles for SAML", draft-ietf-abfab-aaa-saml-03 (work
in progress), March 2012.
[I-D.ietf-emu-chbind]
Hartman, S., Clancy, T., and K. Hoeper, "Channel Binding
Support for EAP Methods", draft-ietf-emu-chbind-16 (work
in progress), May 2012.
10.2. Informative References 10.2. Informative References
[RFC2903] de Laat, C., Gross, G., Gommans, L., Vollbrecht, J., and
D. Spence, "Generic AAA Architecture", RFC 2903,
August 2000.
[I-D.nir-tls-eap] [I-D.nir-tls-eap]
Nir, Y., Sheffer, Y., Tschofenig, H., and P. Gutmann, "A Nir, Y., Sheffer, Y., Tschofenig, H., and P. Gutmann, "A
Flexible Authentication Framework for the Transport Layer Flexible Authentication Framework for the Transport Layer
Security (TLS) Protocol using the Extensible Security (TLS) Protocol using the Extensible
Authentication Protocol (EAP)", draft-nir-tls-eap-13 (work Authentication Protocol (EAP)", draft-nir-tls-eap-13 (work
in progress), December 2011. in progress), December 2011.
[I-D.ietf-oauth-v2] [I-D.ietf-oauth-v2]
Hammer-Lahav, E., Recordon, D., and D. Hardt, "The OAuth Hammer-Lahav, E., Recordon, D., and D. Hardt, "The OAuth
2.0 Authorization Framework", draft-ietf-oauth-v2-26 (work 2.0 Authorization Framework", draft-ietf-oauth-v2-28 (work
in progress), May 2012. in progress), June 2012.
[I-D.iab-privacy-considerations] [I-D.iab-privacy-considerations]
Cooper, A., Tschofenig, H., Aboba, B., Peterson, J., and Cooper, A., Tschofenig, H., Aboba, B., Peterson, J., and
J. Morris, "Privacy Considerations for Internet J. Morris, "Privacy Considerations for Internet
Protocols", draft-iab-privacy-considerations-02 (work in Protocols", draft-iab-privacy-considerations-02 (work in
progress), March 2012. progress), March 2012.
[RFC4017] Stanley, D., Walker, J., and B. Aboba, "Extensible [RFC4017] Stanley, D., Walker, J., and B. Aboba, "Extensible
Authentication Protocol (EAP) Method Requirements for Authentication Protocol (EAP) Method Requirements for
Wireless LANs", RFC 4017, March 2005. Wireless LANs", RFC 4017, March 2005.
skipping to change at page 38, line 21 skipping to change at page 41, line 36
Cantor, S., Kemp, J., Philpott, R., and E. Maler, Cantor, S., Kemp, J., Philpott, R., and E. Maler,
"Assertions and Protocol for the OASIS Security Assertion "Assertions and Protocol for the OASIS Security Assertion
Markup Language (SAML) V2.0", OASIS Standard saml-core- Markup Language (SAML) V2.0", OASIS Standard saml-core-
2.0-os, March 2005. 2.0-os, March 2005.
[RFC2904] Vollbrecht, J., Calhoun, P., Farrell, S., Gommans, L., [RFC2904] Vollbrecht, J., Calhoun, P., Farrell, S., Gommans, L.,
Gross, G., de Bruijn, B., de Laat, C., Holdrege, M., and Gross, G., de Bruijn, B., de Laat, C., Holdrege, M., and
D. Spence, "AAA Authorization Framework", RFC 2904, D. Spence, "AAA Authorization Framework", RFC 2904,
August 2000. August 2000.
[I-D.hartman-emu-mutual-crypto-bind]
Hartman, S., Wasserman, M., and D. Zhang, "EAP Mutual
Cryptographic Binding",
draft-hartman-emu-mutual-crypto-bind-00 (work in
progress), March 2012.
[WS-TRUST] [WS-TRUST]
Lawrence, K., Kaler, C., Nadalin, A., Goodner, M., Gudgin, Lawrence, K., Kaler, C., Nadalin, A., Goodner, M., Gudgin,
M., Barbir, A., and H. Granqvist, "WS-Trust 1.4", OASIS M., Barbir, A., and H. Granqvist, "WS-Trust 1.4", OASIS
Standard ws-trust-200902, February 2009, <http:// Standard ws-trust-200902, February 2009, <http://
docs.oasis-open.org/ws-sx/ws-trust/v1.4/ws-trust.html>. docs.oasis-open.org/ws-sx/ws-trust/v1.4/ws-trust.html>.
URIs URIs
[1] <http://www.openid.net> [1] <http://www.openid.net>
[2] <http://www.eduroam.org> [2] <http://www.eduroam.org>
Editorial Comments
[anchor4] JLS: Add section on discussion EAP methods and
requirements there on
[anchor9] JLS: I don't believe this is a true statement - check it
with Josh and Sam.
Authors' Addresses Authors' Addresses
Josh Howlett Josh Howlett
JANET(UK) JANET(UK)
Lumen House, Library Avenue, Harwell Lumen House, Library Avenue, Harwell
Oxford OX11 0SG Oxford OX11 0SG
UK UK
Phone: +44 1235 822363 Phone: +44 1235 822363
Email: Josh.Howlett@ja.net Email: Josh.Howlett@ja.net
 End of changes. 81 change blocks. 
259 lines changed or deleted 469 lines changed or added

This html diff was produced by rfcdiff 1.48. The latest version is available from http://tools.ietf.org/tools/rfcdiff/