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 libraries that don´t use the async/await and for me it is fundamental.

One library that I think should use asyn/await but that I saw does not use it is Xamarin.Auth!

For uisng Xamarin.Auth.OAuth2Authenticator for authentication I recommend the following solution.

For Xamarin.Android

public async Task<Account> 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));
         }
     };
     try
     {
         auth.Completed += d1;
         var intent = auth.GetUI(activity);
         activity.StartActivity(intent);
         var result= await tcs1.Task;
         return result.Account;
     }
     catch (Exception)
     {
         // todo you should 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(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 added 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.