Is it possible to use an external Identity Provider in a Web API with ASP.NET 5?

Reading this question, @Pinpoint’s answer and the further discussion on comments, I’m well aware that natively we can’t add an identity provider to our apps developed with ASP.NET 5. One possible replacement for the legacy OAuthAuthorizationServerMiddleware is then provided by the AspNet.Security.OpenIdConnect.Server as I’ve found in many places.

ASP.NET OAuth Authorization – Difference between using ClientId and Secret and Username and Password

I’m trying to implement a simple OAuthAuthorizationServerProvider in ASP.NET WebAPI 2. My main purpose is to learn how to have a token for a mobile app. I would like users to login with username & password, and then receive a token (and a refresh token so they won’t have to re-enter credentials once token expires). Later on, I would like to have the chance to open the API for external use by other applications (like one uses Facebook api and such…).