Using Xamarin.Auth.OAuth2Authenticator with async/await

Since Xamarin published the Xamarin 3 I have been playing with this.

Normally I develop apps for Windows Phone and Windows Store, and when i started to use some libraries related with Xamarin, I found some that libraries don´t use the async/awaitconcept, and for me is a fundamental.

One library that I think should use async/await but that I saw don´t use is the Xamarin.Auth!

For how that uses Xamarin.Auth.OAuth2Authenticator for authentication I recommend this solution:

For Xamarin.Android

public async Task<AuthenticatorCompletedEventArgs> LoginAsync(Activity activity, bool allowCancel)
        {
             var auth = new OAuth2Authenticator(
               clientId: "<scopes here>",
               scope: "<scopes here>",
               authorizeUrl: new Uri("<url here>"),
               redirectUrl: new Uri("<url here>"))
            {
                AllowCancel = allowCancel
            };

            // If authorization succeeds or is canceled, .Completed will be fired.
             var tcs1 = new TaskCompletionSource<AuthenticatorCompletedEventArgs>();
            EventHandler<AuthenticatorCompletedEventArgs> d1 =
                (o, e) =>
                {
                    try
                    {
                        tcs1.TrySetResult(e);
                    }
                    catch (Exception ex)
                    {
                        tcs1.TrySetResult(new AuthenticatorCompletedEventArgs(null));
                    }
                };
            auth.Completed += d1;
            var intent = auth.GetUI(activity);
            activity.StartActivity(intent);
            var result = await tcs1.Task;
            auth.Completed -= d1;
            return result;
        }

And then we need to call it this way:

var authService = new AuthService();
var result = await authService.LoginAsync(this, allowCancel);

For Xamarin.IOS

public async Task<Account> LoginAsync(DialogViewController dialog, bool allowCancel)
        {

            var auth = new OAuth2Authenticator(
               clientId: "<scopes here>",
               scope: "<scopes here>",
               authorizeUrl: new Uri("<url here>"),
               redirectUrl: new Uri("<url here>"))
            {
                AllowCancel = allowCancel
            };

            // If authorization succeeds or is canceled, .Completed will be fired.
            var tcs1 = new TaskCompletionSource<AuthenticatorCompletedEventArgs>();
            EventHandler<AuthenticatorCompletedEventArgs> d1 =
                (o, e) =>
                {
                    try
                    {
                        tcs1.TrySetResult(e);
                    }
                    catch (Exception ex)
                    {
                       tcs1.TrySetResult(new AuthenticatorCompletedEventArgs(null));
                    }
                };

            try
            {
                auth.Completed += d1;
                var vc = auth.GetUI();
                dialog.PresentViewController(vc, true, null);
                var result= await tcs1.Task;
                return result.Account;
            }
            catch (Exception)
            {
               // todo handle the exception
                return null;
            }
            finally
            {
                auth.Completed -= d1;
            }
        }

And then we need to call it this way:

var authService = new AuthService();
var result = await authService.LoginAsync(dialog, allowCancel);

In conclusion, i think it is very simple to use and i think it should be add to the Xamarin.Auth.

I added the sample to:
https://github.com/saramgsilva/Xamarin.Auth/tree/master/samples

and will do a pull request for the original repository.