The Federated Web Single-Sign-On (SSO) design in Active Directory Federation Services (AD FS) 2.0 involves secure communication that spans multiple firewalls, perimeter networks, and name-resolution servers—in addition to the entire Internet routing infrastructure.
Typically, this design is used when two organizations agree to create a federation trust relationship to allow users in one organization (the account partner organization) to access Web-based applications or services, which are secured by AD FS 2.0, in the other organization (the resource partner organization).
In other words, a federation trust relationship is the embodiment of a business-level agreement or partnership between two organizations. As shown in the following illustration, you can establish a federation trust relationship between two businesses, which results in an end-to-end federation scenario.

In this Federated Web SSO design, two federation servers (one in Fabrikam and the other in Contoso) route authentication requests from user accounts in Fabrikam to Web-based applications or services in Contoso.
![]() | |
---|---|
For additional security, you can use federation server proxies to relay requests to federation servers that are not directly accessible from the Internet. |
Contoso is the resource provider. The Contoso portion of the Federated Web SSO design achieves the following AD FS 2.0 deployment goals:
More Here
Courtesy:http://technet.microsoft.com/en-us/library/dd807050%28WS.10%29.aspx