Microsoft’s new framework for writing RESTful web services and web APIs is appropriately enough called ASP.NET Web API. As the name applies, this technology is part of ASP.NET and also inherits its well-known security architecture. But in addition it also supports a number of new extensibility points and a flexible hosting infrastructure outside of IIS. There are a number of ways how to do authentication and authorization in Web API - from Windows to usernames and passwords up to token based authentication and everything in between. This talk explores the various options, and puts special focus on technologies like claims, SAML, OAuth2, Simple Web Tokens and delegation.