Initiate login for custom stories

FB.login(function(response) {
    if (response.authResponse) {
        // The person logged into your app
    } else {
        // The person cancelled the login dialog
    }
});

FB.getLoginStatus(function(response) {
   if (response.status === 'connected') {
     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.
   }
  });