public static void Register(HttpConfiguration config)
        {
            CorsConfiguration corsConfig = new CorsConfiguration();
            corsConfig.AllowAll();
            var corsHandler = new CorsMessageHandler(corsConfig, config);
            config.MessageHandlers.Add(corsHandler);

            // authentication configuration for identity controller
            var authentication = CreateAuthenticationConfiguration();
            config.MessageHandlers.Add(new AuthenticationHandler(authentication));

            // default API route
            config.Routes.MapHttpRoute(
                name: "DefaultApi",
                routeTemplate: "api/{controller}/{id}",
                defaults: new { id = RouteParameter.Optional }
            );
        }