How to check logged in facebook user in ASP.NET MVC 4?

Question

I want to check if a user is already logged in with facebook in ASP.NET MVC4. I'm using Facebook C# SDK. I have this code for getting the access_token from facebook:

  public ActionResult FacebookCallback(string code)
    {
        var fb = new FacebookClient();
        dynamic result = fb.Post("oauth/access_token", new
        {
            client_id = "XXXXXXXXXXXXXX",
            client_secret = "XXXXXXXXXXXXXXXXXXX",
            redirect_uri = RedirectUri.AbsoluteUri,
            code = code
        });

        var accessToken = result.access_token;

        Session["AccessToken"] = accessToken;

        fb.AccessToken = accessToken;

        dynamic me = fb.Get("me?fields=first_name,last_name,id,email");
        string email = me.email;

        FormsAuthentication.SetAuthCookie(email, false);
        return RedirectToAction("Index", "Home");
    }

I don't know how to check if user is already logged in. Please help.

Answer 1

The most easiest way in my opinion if your willing to checkout Facebooks javascript SDK, then there is a FB.getLoginStatus method which will give you the info you need.

Taken from facebook's dev site:

FB.getLoginStatus(function(response) {
  if (response.status === 'connected') {
    // the user is logged in and has authenticated your
    // app, and response.authResponse supplies
    // the user's ID, a valid access token, a signed
    // request, and the time the access token 
    // and signed request each expire
    var uid = response.authResponse.userID;
    var accessToken = response.authResponse.accessToken;
  } else if (response.status === 'not_authorized') {
    // the user is logged in to Facebook, 
    // but has not authenticated your app
  } else {
    // the user isn't logged in to Facebook.
  }
});

There is also the user_online_presence extended permission here . Probably not what you want, but using FQL, you can request the online_presence field here , but note this only returns if the user is logged into facebook user chat.