private async void btnLogin(object sender, RoutedEventArgs e)
        {
            validate();
            Dictionary <String, String> loginInfo = new Dictionary <string, string>();

            loginInfo.Add("email", this.Email.Text);
            loginInfo.Add("password", this.Password.Password);
            HttpClient    httpClient = new HttpClient();
            StringContent content    = new StringContent(JsonConvert.SerializeObject(loginInfo), System.Text.Encoding.UTF8, "application/json");
            var           response   = httpClient.PostAsync("https://2-dot-backup-server-002.appspot.com/_api/v2/members/authentication", content).Result;

            var responseContent = await response.Content.ReadAsStringAsync();

            if (response.StatusCode == System.Net.HttpStatusCode.Created)
            {
                // save file...
                Debug.WriteLine(responseContent);
                // Doc token
                TokenResponse token = JsonConvert.DeserializeObject <TokenResponse>(responseContent);

                // Luu token
                StorageFolder folder = ApplicationData.Current.LocalFolder;
                StorageFile   file   = await folder.CreateFileAsync("token.txt", CreationCollisionOption.ReplaceExisting);

                await FileIO.WriteTextAsync(file, responseContent);

                // Lay thong tin ca nhan bang token.
                HttpClient client2 = new HttpClient();
                client2.DefaultRequestHeaders.Add("Authorization", "Basic " + token.token);
                var resp         = client2.GetAsync("http://2-dot-backup-server-002.appspot.com/_api/v2/members/information").Result;
                var responseInfo = await resp.Content.ReadAsStringAsync();

                Member infoUser = JsonConvert.DeserializeObject <Member>(responseInfo);
                memberOld.avatar    = infoUser.avatar;
                memberOld.address   = infoUser.address;
                memberOld.birthday  = infoUser.birthday;
                memberOld.email     = infoUser.email;
                memberOld.firstName = infoUser.firstName;
                memberOld.gender    = infoUser.gender;
                memberOld.lastName  = infoUser.lastName;
                memberOld.phone     = infoUser.phone;
                memberOld.id        = infoUser.id;
                var messageDialog = new MessageDialog("Login successful .");
                await messageDialog.ShowAsync();

                FrameLogin.Navigate(typeof(MainPage));
            }
            else
            {
                // Xu ly loi.
                ErrorResponse errorObject = JsonConvert.DeserializeObject <ErrorResponse>(responseContent);
                if (errorObject != null && errorObject.error.Count > 0)
                {
                    foreach (var key in errorObject.error.Keys)
                    {
                        ContentValidate.Text = "Email or password invalid";
                    }
                }
            }
        }
        private async void  autoLogin( )
        {
            try
            {
                LoadingIndicator.IsActive = true;
                StorageFile config_login = await ApplicationData.Current.LocalFolder.GetFileAsync("token.txt");

                String info = await FileIO.ReadTextAsync(config_login);

                JObject    data    = JObject.Parse(info);
                var        token   = ((data.SelectToken("token")));
                HttpClient client2 = new HttpClient();
                client2.DefaultRequestHeaders.Add("Authorization", "Basic " + token);
                var resp         = client2.GetAsync("http://2-dot-backup-server-002.appspot.com/_api/v2/members/information").Result;
                var responseInfo = await resp.Content.ReadAsStringAsync();

                Member infoUser = JsonConvert.DeserializeObject <Member>(responseInfo);
                if (resp.StatusCode == System.Net.HttpStatusCode.Created)
                {
                    FrameLogin.Navigate(typeof(MainPage));
                    memberOld.avatar          = infoUser.avatar;
                    memberOld.address         = infoUser.address;
                    memberOld.birthday        = infoUser.birthday;
                    memberOld.email           = infoUser.email;
                    memberOld.firstName       = infoUser.firstName;
                    memberOld.gender          = infoUser.gender;
                    memberOld.lastName        = infoUser.lastName;
                    memberOld.phone           = infoUser.phone;
                    memberOld.id              = infoUser.id;
                    LoadingIndicator.IsActive = false;
                }
                else
                {
                }
            } catch (FileNotFoundException)
            {
            }
        }