IdentityServer is a light-weight, .NET based security token service that supports various protocols and token formats.
Based on .NET 4.5/MVC 4/WCF/Web API
Based on .NET 4.0/WIF/MVC 3/WCF
Helper library for claims-based identity, access control and token based authentication for .NET, MVC, WCF and Web API.
AuthorizationServer is the foundation for implementing API authorization. It does so by providing an implementation of the OAuth2 authorization framework.