public static async Task Authorize()
        {
            var state = Guid.NewGuid().ToString("N");
            var authorizeUri = DropboxOAuth2Helper.GetAuthorizeUri(OAuthResponseType.Code, App.AppKey, App.RedirectUri);

            var http = new HttpListener();
            http.Prefixes.Add(App.RedirectUri.OriginalString);
            http.Start();

            // Launch the URI
            var success = await Windows.System.Launcher.LaunchUriAsync(authorizeUri);

            if (success)
            {
                await HandleOAuth2Redirect(http);
                var result = await HandleJSRedirect(http);
                if (result.State != state)
                {
                    return;
                }

                App.AccessToken = result.AccessToken;
            }
            else
            {
                // URI launch failed
            }
        }

        private static async Task HandleOAuth2Redirect(HttpListener http)
        {
            var context = await http.GetContextAsync();
            //while (context.Request.Url.AbsolutePath != App.RedirectUri.AbsolutePath)
            //    await HandleJSRedirect(http);
            // We only care about request to RedirectUri endpoint.
            while (context.Request.Url.AbsolutePath != App.RedirectUri.AbsolutePath)
            {
                context = await http.GetContextAsync();
            }

            // Respond with a HTML page which runs JS to send URl fragment.
            context.Response.ContentType = "text/html";

            // Respond with a page which runs JS and sends URL fragment as query string
            // to TokenRedirectUri.
            using (var file = System.IO.File.OpenRead("index.html"))
            {
                file.CopyTo(context.Response.OutputStream);
            }

            context.Response.OutputStream.Close();
        }

        private static async Task<OAuth2Response> HandleJSRedirect(HttpListener http)
        {
            var context = await http.GetContextAsync();

            // We only care about request to TokenRedirectUri endpoint.
            while (context.Request.Url.AbsolutePath != App.RedirectUri.AbsolutePath)
            {
                context = await http.GetContextAsync();
            }

            var redirectUri = new Uri(context.Request.QueryString["url_with_fragment"]);

            var result = DropboxOAuth2Helper.ParseTokenFragment(redirectUri);

            return result;
        }