ArcGISRuntimeXamarin.Forms.iOS.OAuthPageiOS.AuthorizeAsync C# (CSharp) Method

        public Task<IDictionary<string, string>> AuthorizeAsync(Uri serviceUri, Uri authorizeUri, Uri callbackUri)
        {
            // If the TaskCompletionSource is not null, authorization is in progress
            if (_taskCompletionSource != null)
            {
                // Allow only one authorization process at a time
                throw new Exception();
            }

            // Create a task completion source
            _taskCompletionSource = new TaskCompletionSource<IDictionary<string, string>>();

            // Create a new Xamarin.Auth.OAuth2Authenticator using the information passed in
            Xamarin.Auth.OAuth2Authenticator auth = new OAuth2Authenticator(
                clientId: OAuthPage.AppClientId,
                scope: "",
                authorizeUrl: new Uri(OAuthPage.AuthorizeUrl),
                redirectUrl: new Uri(OAuthPage.OAuthRedirectUrl));

            // Allow the user to cancel the OAuth attempt
            auth.AllowCancel = true;

            // Define a handler for the OAuth2Authenticator.Completed event
            auth.Completed += (sender, authArgs) =>
            {
                try
                {
                    // Dismiss the OAuth UI when complete
                    this.DismissViewController(true, null);

                    // Throw an exception if the user could not be authenticated
                    if (!authArgs.IsAuthenticated)
                    {
                        throw new Exception("Unable to authenticate user.");
                    }

                    // If authorization was successful, get the user's account
                    Xamarin.Auth.Account authenticatedAccount = authArgs.Account;

                    // Set the result (Credential) for the TaskCompletionSource
                    _taskCompletionSource.SetResult(authenticatedAccount.Properties);
                }
                catch (Exception ex)
                {
                    // If authentication failed, set the exception on the TaskCompletionSource
                    _taskCompletionSource.SetException(ex);
                }
            };

            // If an error was encountered when authenticating, set the exception on the TaskCompletionSource
            auth.Error += (sndr, errArgs) =>
            {
                if (errArgs.Exception != null)
                {
                    _taskCompletionSource.TrySetException(errArgs.Exception);
                }
                else
                {
                    _taskCompletionSource.TrySetException(new Exception(errArgs.Message));
                }
            };

            // Present the OAuth UI (on the app's UI thread) so the user can enter user name and password
            InvokeOnMainThread(() =>
            {
                this.PresentViewController(auth.GetUI(), true, null);
            });

            // Return completion source task so the caller can await completion
            return _taskCompletionSource.Task;
        }
        #endregion