private async void PageRootLoaded(object sender, RoutedEventArgs e)
        {
            if (AccessToken != null) return;

            var f = new Flickr("dbc316af64fb77dae9140de64262da0a", "0781969a058a2745");
            var requestToken = await GetRequestToken();
            string output;
            var flickrUri = new Uri(f.OAuthCalculateAuthorizationUrl(requestToken.Token, AuthLevel.Delete));
            var webAuthenticationResult = await WebAuthenticationBroker.AuthenticateAsync(
                                                    WebAuthenticationOptions.None,
                                                    flickrUri);

            if (webAuthenticationResult.ResponseStatus == WebAuthenticationStatus.Success)
            {
                output = webAuthenticationResult.ResponseData;
                AccessToken = await f.OAuthAccessTokenAsync(requestToken.Token, requestToken.TokenSecret, output);

                LoadDataSource(AccessToken);
            }
            else if (webAuthenticationResult.ResponseStatus == WebAuthenticationStatus.ErrorHttp)
            {
                output = "HTTP Error returned by AuthenticateAsync() : " + webAuthenticationResult.ResponseErrorDetail.ToString();
            }
            else if (webAuthenticationResult.ResponseStatus == WebAuthenticationStatus.UserCancel)
            {
                output = "Authentication process was cancelled by the user";
            } 
        }