Window identity foundation (WIF) enables .NET developers to externalize identity logic from their application, improving developer productivity, enhancing application security, and enabling interoperability.
It is part of Microsoft's identity and access management Solution built on Active Directory that also includes:
1) Active Directory Federation Services 2.0 : a security token service for IT that issues and transforms claims and other tokens, manages user access and enables federation and access management for simplified SSO (Single Sign-on)
2) Windows Azure Access Control Services: provides an easy way to provide identity and access control to web applications and services.
Source: MSDN | |