public async Task<bool> LoginUserAsync (User user)
		{
//			var authData = string.Format ("{0}:{1}", user.Username, user.Password);
//			var authHeaderValue = Convert.ToBase64String (Encoding.UTF8.GetBytes (authData));
//
//			client = new HttpClient ();
//			client.MaxResponseContentBufferSize = 256000;
//			client.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue ("Basic", authHeaderValue);

			var handler = new HttpClientHandler {
				Credentials = new NetworkCredential(user.Username, user.Password)
			};

			// Use username/password credentials.
			client = new HttpClient(handler);
			client.MaxResponseContentBufferSize = 256000;

			var uri = new Uri (string.Format (Constants.RestUrl, string.Empty));
			bool auth = false;

			Debug.WriteLine("GET: " + uri);

			try {
				HttpResponseMessage response = await client.GetAsync (uri);
				HttpContent content = response.Content;

				// Check status code.
				Debug.WriteLine("Response StatusCode: " + (int)response.StatusCode);

				// Read the string.
				string result = await content.ReadAsStringAsync();

				// Display the result.
				if (result != null && result.Length >= 50) {
//					Debug.WriteLine(result.Substring(0, 50) + "...");
					Debug.WriteLine(result);
				}

				if (response.IsSuccessStatusCode) {
					auth = true;

					return auth;
				}
			} catch (Exception ex) {
				Debug.WriteLine (@"ERROR {0}", ex.Message);
			}

			return auth;
		}
 public Task<bool> CheckCredentialAsync(User user)
 {
     return service.LoginUserAsync (user);
 }