public OpenIdentity Verify()
        {
            var fb = new FacebookClient();

            IAuthorizationState authorization = fb.ProcessUserAuthorization();

            var request = WebRequest.Create("https://graph.facebook.com/me?access_token=" + Uri.EscapeDataString(authorization.AccessToken));
            using (var response = request.GetResponse())
            {
                using (var responseStream = response.GetResponseStream())
                {
                    var graph = FacebookGraph.Deserialize(responseStream);
                    return new OpenIdentity()
                               {Id = graph.Id.ToString(), Username = graph.Name, SiteProvider = "Facebook"};
                }
            }
        }
        public void Authenticate(Uri callback)
        {
            var fb = new FacebookClient();

               fb.RequestUserAuthorization(returnTo:callback);
        }