How to handle single login for request in Web API 2? and How to consume WCF service inside Web API 2?

I have the following layers: 1)Mobile App. 2)Web API 2. 3)WCF Rest Service (Which include login method).

The mobile application will make a request to Web API,I want to centralize the login method in one place to handle all requests and this login method will consume login method in WCF Rest which return true/false to generate token to mobile app.