private void OAuthGetToken_GetResponseCallback(IAsyncResult asynchronousResult)
        {
            try
            {
                var webReq = (System.Net.HttpWebRequest)asynchronousResult.AsyncState;
                var webRes = (System.Net.HttpWebResponse)webReq.EndGetResponse(asynchronousResult);

                var stream = webRes.GetResponseStream();
                var result = new StreamReader(stream).ReadToEnd();

                // {"token_type":"bearer","access_token":"AAAAAAAAAAAAAAAAAAAAAPPMVwAAAAAA77uFK8FCnOnw5HagSCNxY93HjXo%3D0Ty2nkgdSIE0JSz0gTfaA3P6yaAS7V81fUm9JmdD9LYTzrCgc4"}
                this.accessToken = JsonConvert.DeserializeObject <OAuth2AccessToken>(result);

                this.WriteLog("TokenType={0}, AccessToken={1}", accessToken.token_type, accessToken.access_token);
            }
            catch (Exception ex)
            {
                this.WriteLog("{0}", ex.Message);
            }
        }
 public MainPage()
 {
     this.InitializeComponent();
     this.synchronizationContext = System.Threading.SynchronizationContext.Current;
     this.accessToken            = null;
 }