In previous posts we get to know with ASP.NET Identity and use it in many platforms such as Desktop or Android application. In all of them, I used local identity management system of ASP.NET Identity which connects to local database and manages users. So if users want to use our services, they have to register an account with our systems. They can’t use their Facebook or Google account to login to our system. Today I’ll show you how to extend our services by enabling OAuth 2 so that the users can authenticate themselves with their Facebook, Google+, Microsoft or Twitter accounts. You may find a lot of tutorials out there in Internet for integrating this external authentication within a web application. Therefore I wouldn’t like to write the same thing again but I will use a WPF application as my client and authenticate with ASP.NET Identity service over external authentication of Google+. This concept can be also used for mobile application such as Android, IOS or Windows Phone.