Facebook.FacebookClient.ParseOAuthCallbackUrl C# (CSharp) Method

        public virtual FacebookOAuthResult ParseOAuthCallbackUrl(Uri uri)
        {
            var parameters = new Dictionary<string, object>();

            bool found = false;
            if (!string.IsNullOrEmpty(uri.Fragment))
            {
                // #access_token and expries_in are in fragment
                var fragment = uri.Fragment.Substring(1);
                ParseUrlQueryString("?" + fragment, parameters, true);

                if (parameters.ContainsKey("access_token"))
                    found = true;
            }

            // code, state, error_reason, error and error_description are in query
            // ?error_reason=user_denied&error=access_denied&error_description=The+user+denied+your+request.
            var queryPart = new Dictionary<string, object>();
            ParseUrlQueryString(uri.Query, queryPart, true);

            if (queryPart.ContainsKey("code") || (queryPart.ContainsKey("error") && queryPart.ContainsKey("error_description")))
                found = true;

            foreach (var kvp in queryPart)
                parameters[kvp.Key] = kvp.Value;

            if (found)
                return new FacebookOAuthResult(parameters);

            throw new InvalidOperationException("Could not parse Facebook OAuth url.");
        }

        public ActionResult FbAuth(string returnUrl)
        {
            var client = new FacebookClient();
            var oauthResult = client.ParseOAuthCallbackUrl(Request.Url);

            // Build the Return URI form the Request Url
            var redirectUri = new UriBuilder(Request.Url);
            redirectUri.Path = Url.Action("FbAuth", "Account");

            dynamic result = client.Get("/oauth/access_token", new
            {
            client_id = ConfigurationManager.AppSettings["FacebookAppId"],
            redirect_uri = redirectUri.Uri.AbsoluteUri,
            client_secret = ConfigurationManager.AppSettings["FacebookAppSecret"],
            code = oauthResult.Code,
            });

            // Read the auth values
            string accessToken = result.access_token;
            DateTime expires = DateTime.UtcNow.AddSeconds(Convert.ToDouble(result.expires));

            dynamic me = client.Get("/me", new { fields = "first_name,last_name,email", access_token = accessToken });

            // Read the Facebook user values
            long facebookId = Convert.ToInt64(me.id);
            string firstName = me.first_name;
            string lastName = me.last_name;
            string email = me.email;

            // Add the user to our persistent store
            var userService = new UserService();
            userService.AddOrUpdateUser(new User
            {
            Id = facebookId,
            FirstName = firstName,
            LastName = lastName,
            Email = email,
            AccessToken = accessToken,
            Expires = expires
            });

            // Set the Auth Cookie
            FormsAuthentication.SetAuthCookie(email, false);

            // Redirect to the return url if availible
            if (String.IsNullOrEmpty(returnUrl))
            {
            return Redirect("/App");
            }
            else
            {
            return Redirect(returnUrl);
            }
        }