ASP.NET Web Api Authentication Methods

I am trying to implement authentication for my web api. I have read about different techniques of api authentication and the token technique is the most reasonable for me.

I read different articles about how to implement token based authentication in asp.net but they all rely on different libraries such as OAuth or Owin which also provide their own method of database interactions.

The thing is that I have already implemented database interaction with abstract repositories and entities and I would like to find out how can I implement api authentication easily and simply without interfering with my current design.

(By the way, my project is built on top of an empty web api project, so it doesn't come with all the bootstrap and authentication classes).

Thank you

via Chebli Mohamed