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The Depth of SAML

12.01.2011
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Security Assertion Markup Language (SAML) is an XML standard for exchanging authentication and authorization data between entities which is a product of the OASIS Security Services Technical Committee.

- SAML 1.0 was adopted as an OASIS standard in Nov 2002
- SAML 1.1 was ratified as an OASIS standard in Sept 2003
- SAML 2.0 became an OASIS standard in Mar 2005

Liberty Alliance donated its Identity Federation Framework (ID-FF) specification to OASIS, which became the basis of the SAML 2.0 specification. Thus SAML 2.0 represents the convergence of SAML 1.1, Liberty ID-FF 1.2, and Shibboleth 1.3.

2. SAML base standards

SAML is built upon the following technology standards.

- Extensible Markup Language (XML)
- XML Schema
- XML Signature
- XML Encryption (SAML 2.0 only)
- Hypertext Transfer Protocol (HTTP)
- SOAP

3. SAML Components

Assertions: Authentication, Attribute and Authorization information
Protocol: Request and Response elements for packaging assertions
Bindings: How SAML Protocols map onto standard messaging or communication protocols
Profiles: How SAML protocols, bindings and assertions combine to support a defined use case

4. Assertions and Protocols for SAML v2.0

The Security Assertion Markup Language (SAML) defines the syntax and processing semantics of assertions made about a subject by a system entity. In the course of making, or relying upon such assertions, SAML system entities may use other protocols to communicate either regarding an assertion itself, or the subject of an assertion. This specification defines both the structure of SAML assertions, and an associated set of protocols, in addition to the processing rules involved in managing a SAML system. This specification is considered as the SAML Core specification and these constructs are typically embedded in other structures for transport, such as HTTP form POSTs and XML-encoded SOAP messages.

5. Bindings for SAML v2.0

Bindings for SAML specifies SAML protocol bindings for the use of SAML assertions and request-response messages in communications protocols and frameworks.

Mappings of SAML request-response message exchanges onto standard messaging or communication protocols are called SAML protocol bindings (or just bindings). An instance of mapping SAML requestresponse message exchanges into a specific communication protocol <FOO> is termed a binding for SAML or a SAML <FOO> binding. For example, a SAML SOAP binding describes how SAML request and response message exchanges are mapped into SOAP message exchanges.

The intent of this specification is to specify a selected set of bindings in sufficient detail to ensure that independently implemented SAML-conforming software can interoperate when using standard messaging or communication protocols.

Following bindings are covered under this specification.

- SAML SOAP Binding
- Reverse SOAP (PAOS) Binding
- HTTP Redirect Binding
- HTTP POST Binding
- HTTP Artifact Binding
- SAML URI Binding

6. Profiles for SAML v2.0

Profiles for SAML specifies profiles that define the use of SAML assertions and request-response messages in communications protocols and frameworks, as well as profiles that define SAML attribute value syntax and naming conventions.

One type of SAML profile outlines a set of rules describing how to embed SAML assertions into and extract them from a framework or protocol. Such a profile describes how SAML assertions are embedded in or combined with other objects (for example, files of various types, or protocol data units of communication protocols) by an originating party, communicated from the originating party to a receiving party, and subsequently processed at the destination. A particular set of rules for embedding SAML assertions into and extracting them from a specific class of <FOO> objects is termed a <FOO> profile of SAML.

For example, a SOAP profile of SAML describes how SAML assertions can be added to SOAP messages, how SOAP headers are affected by SAML assertions, and how SAML-related error states should be reflected in SOAP messages.

Another type of SAML profile defines a set of constraints on the use of a general SAML protocol or assertion capability for a particular environment or context of use. Profiles of this nature may constrain optionality, require the use of specific SAML functionality (for example, attributes, conditions, or bindings), and in other respects define the processing rules to be followed by profile actors.

Following profiles are covered under this specification.

- SSO Profiles of SAML [Web Browser SSO Profile,Enhanced Client or Proxy (ECP) Profile, Identity Provider Discovery Profile, Single Logout Profile, Name Identifier Management Profile]
- Artifact Resolution Profile
- Assertion Query/Request Profile
- Name Identifier Mapping Profile
- SAML Attribute Profiles

7. Metadata for SAML v2.0

SAML profiles require agreements between system entities regarding identifiers, binding support and endpoints, certificates and keys, and so forth. A metadata specification is useful for describing this information in a standardized way. This specification defines an extensible metadata format for SAML system entities, organized by roles that reflect SAML profiles. Such roles include that of SSO Identity Provider, SSO Service Provider, Affiliation, Attribute Authority, Attribute Requester, and Policy Decision Point.

This specification further defines profiles for the dynamic exchange of metadata among system entities, which may be useful in some deployments.

8. Conformance Requirements for SAML v2.0

This normative specification describes features that are mandatory and optional for implementations claiming conformance to SAML V2.0 and also specifies the entire set of documents comprising SAML V2.0.

9. Web Services Security: SAML Token Profile 1.1

This specification describes how to use SAML V1.1 and V2.0 assertions with the Web Services Security SOAP Message Security V1.1 specification.

10. SAML 2.0 profile of XACML

The OASIS eXtensible Access Control Markup Language [XACML] is a powerful, standard
language that specifies schemas for authorization policies and for authorization decision requests and responses.

This profile defines how to use SAML 2.0 to protect, transport, and request XACML schema instances and other information needed by an XACML implementation.

11. Security and Privacy Considerations for SAML

This non-normative document describes and analyzes the security and privacy properties of SAML defined in the core SAML specification and the SAML bindings and profiles specifications.

12. SAML V2.0 Kerberos Attribute Profile

This specification defines an attribute profile for the Kerberos protocol. The SAML V2.0 Kerberos Attribute Profile describes a SAML attribute profile for requesting and expressing Kerberos protocol messages. In this version of the specification, this is constrained to the Kerberos KRB-CRED message type. The mechanisms that are used to generate the Kerberos message are outside the scope of this document and are described by IETF RFC 4120: 'The Kerberos Network Authentication Service (V5)'.

13. SAML V2.0 Change Notify Protocol

The SAML V2.0 Change Notify Protocol describes request and response messages for informing SAML endpoints about available changes to subjects and attributes associated with subjects.

Source: http://blog.facilelogin.com/2011/11/depth-of-saml-saml-summary.html
Published at DZone with permission of Prabath Siriwardena, author and DZone MVB.

(Note: Opinions expressed in this article and its replies are the opinions of their respective authors and not those of DZone, Inc.)

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Comments

Ash Mughal replied on Wed, 2012/01/25 - 7:14pm

SAML provides an XML-based framework for creating and exchanging security information between online partners.

The single most important problem that SAML is trying to solve is the Web Browser Single Sign-On  problem, a problem also addressed by the OpenID protocol. Single sing-on solutions are abundant at the intranet level but extending these solutions beyond the intranet has been problematic and has led to the proliferation of non-interoperable proprietary technologies.

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