I am building a couple of JSON web services that will post to the users journal through the Journal API. This works great. 

Now, I am trying to figure out how to build a web service that will "login with facebook" but I cant seem to figure out how to login or register the user with facebook authentication (or google+) on my site. 

I am building an app where the use can take a picture, add a comment and add post. 

When it comes to login and registering, I would like DNN to handle that so when the user downloads the app, the user has the following choices: 

 1. Login with FB 

 2. Login normal 

 or register "manually" without using FB. 

Now, when the user clicks on "Login with FB" I would like to "use" the same execution as is if the user would have clicked "login with FB" on the web page. I would like to call the API that DNN uses and execute it. Anyone knows how to achieve this?

Or is there another way of approaching it? I could connect to FB from my app, but I need a "connection" with my site. Else, if the user "registers" using FB on the app, what happens when the user clicks on "login with FB" on my page? How will my DNN know that the user has "registered" in the app already? And vice versa, if the user logs in with facebook on my page, how will I know that the user used FB on the app to "register"?

Sorry if this sounds confusing, please email me if any one has advice, maybe I am going about this all wrong. amer@healthyheroes.se

Thanx!