Claim Based Authentication

Claim based authentication is a authentication mechanism which acts as an alternative to the traditional username/password mode of authentication. Claim based authentication makes it easy to implement features like Single Sign On, by re-using the same set of security token across multiple applications / services.

In Claim based authentication, the application/service is relieved from implementing the logic to validate a user’s identity; instead the validation is done by an independent Identity Provider, commonly known as Security Token Service (STS)

A Claim is a piece of information specific to a user or an organization, a security token encapsulates a set of claims, the security token is provided by the identity provider and is used by various applications/services to recognize the user.

To accept the security token provided by an Identity Provider, the Application/Service should have a mutual trust/relationship with the Identity Provider.

The user registers with the Identity Provider (STS) gets a security token, and passes the security token to gain access to various applications/service which recognizes the security token.  

The user can send the initial request to the Application/service by embedding the security token with the request, so that he gains instant access to the applications instead of being redirected to the Identity provider’s login page. 

To know more about Claims and Claim based Authentication refer to the Microsoft’s page
http://msdn.microsoft.com/en-us/library/ff359101.aspx