SAML, developed by the Security Services Technical Committee of OASIS, is an XML-based framework for communicating user authentication, entitlement, and attribute information. As its name suggests, SAML allows business entities to make assertions regarding the identity, attributes, and entitlements of a subject (an entity that is often a human user) to other entities, such as a partner company or another enterprise application. Federation is the dominant movement in identity management today. Federation refers to the establishment of some or all of business agreements, cryptographic trust, and user identifiers or attributes across security and policy domains to enable more seamless cross-domain business interactions. As Web services promise to enable integration between business partners through loose coupling at the application and messaging layer, federation does so at the identity management layer — insulating each domain from the details of the others' authentication and authorization infrastructure. Key to this loose coupling at the identity management layer are standardized mechanisms and formats for the communication of identity information between the domains — the standard provides the insulating buffer. SAML defines just such a standard." [FAQ 2006]
May 2003 CS Overview: The Security Assertion Markup Language (SAML) is being developed by the OASIS XML-Based Security Services Technical Committee (SSTC). The Security Assertion Markup Language (SAML) is "an XML-based framework for exchanging security information. This security information is expressed in the form of assertions about subjects, where a subject is an entity (either human or computer) that has an identity in some security domain. A typical example of a subject is a person, identified by his or her email address in a particular Internet DNS domain. Assertions can convey information about authentication acts performed by subjects, attributes of subjects, and authorization decisions about whether subjects are allowed to access certain resources. Assertions are represented as XML constructs and have a nested structure, whereby a single assertion might contain several different internal statements about authentication, authorization, and attributes. Note that assertions containing authentication statements merely describe acts of authentication that happened previously. Assertions are issued by SAML authorities, namely, authentication authorities, attribute authorities, and policy decision points. SAML defines a protocol by which clients can request assertions from SAML authorities and get a response from them. This protocol, consisting of XML-based request and response message formats, can be bound to many different underlying communications and transport protocols; SAML currently defines one binding, to SOAP over HTTP. SAML authorities can use various sources of information, such as external policy stores and assertions that were received as input in requests, in creating their responses. Thus, while clients always consume assertions, SAML authorities can be both producers and consumers of assertions."
Why is SAML required? There are four 'drivers' behind the creation of the SAML standard:
Limitations of Browser cookies: Most existing Single-Sign On products use browser cookies to maintain state so that re-authentication is not required. Browser cookies are not transferred between DNS domains. So, if you obtain a cookie from www.abc.com, then that cookie will not be sent in any HTTP messages to www.xyz.com. This could even apply within an organization that has separate DNS domains. Therefore, to solve the Cross-Domain SSO (CDSSO) problem requires the application of different technology. All SSO products solve the CDSSO problem by different techniques.
SSO Interoperability: How products implement SSO and CDSSO are completely proprietary. If you are an organization and you want to perform SSO across different DNS domains within the same organization or you want to perform CDSSO to trading partners, then you will have to use the same SSO product in all the domains.
Web Services: Security within Web Services is still being defined. Most of the focus has been on how to provide confidentiality and authentication/integrity services on an end-to-end basis. The SAML standard provides the means by which authentication and authorization assertions can exchanged between communicating parties.
Federation: The need to simplify identity management across organizational boundaries, allowing users to consolidate many local identities into a single (or at least a reduced set) Federated Identity..." [excerpted from the Security Assertion Markup Language (SAML) 2.0 Technical Overview, Working Draft 01 22-July-2004.]