public async Task<IHttpActionResult> RegisterUser(UserAccountBindingModel model)
        {
            if (model == null)
            {
                return this.BadRequest("Invalid user data");
            }

            if (!ModelState.IsValid)
            {
                return this.BadRequest(this.ModelState);
            }

            var user = new User
            {
                UserName = model.Username
            };

            var identityResult = await this.UserManager.CreateAsync(user, model.Password);

            if (!identityResult.Succeeded)
            {
                return this.GetErrorResult(identityResult);
            }

            // Auto login after registrаtion (successful user registration should return access_token)
            var loginResult = await this.LoginUser(new UserAccountBindingModel()
            {
                Username = model.Username,
                Password = model.Password
            });
            return loginResult;
        }
        public async Task<IHttpActionResult> LoginUser(UserAccountBindingModel model)
        {
            if (model == null)
            {
                return this.BadRequest("Invalid user data");
            }

            // Invoke the "token" OWIN service to perform the login (POST /api/token)
            var testServer = TestServer.Create<Startup>();
            var requestParams = new List<KeyValuePair<string, string>>
            {
                new KeyValuePair<string, string>("grant_type", "password"),
                new KeyValuePair<string, string>("username", model.Username),
                new KeyValuePair<string, string>("password", model.Password)
            };
            var requestParamsFormUrlEncoded = new FormUrlEncodedContent(requestParams);
            var tokenServiceResponse = await testServer.HttpClient.PostAsync(
                Startup.TokenEndpointPath, requestParamsFormUrlEncoded);

            return this.ResponseMessage(tokenServiceResponse);
        }