var auth = new Google.Apis.Authentication.OAuth2.GoogleAuthenticator (ClientID,
				new Uri ("http://example.com/callback"),
				Google.Apis.Tasks.v1.TasksService.Scopes.Tasks.GetStringValue());

// When we're authenticated, we'll show the tasks from the default list
Action showTasks = () =>
{
	var service = new Google.Apis.Tasks.v1.TasksService (auth);

	// get the tasks from the default task list
	var tasks = service.Tasks.List("@default").Fetch();
	foreach (var task in tasks.Items)
		Console.WriteLine (task.Title);
};

// We don't want to have to login every time, so we'll use the Xamarin.Auth AccountStore
AccountStore store = AccountStore.Create (this);
Account savedAccount = store.FindAccountsForService ("google").FirstOrDefault();
if (savedAccount != null)
{
	this.auth.Account = savedAccount;
	showTasks();
}
else
{
	this.auth.Completed += (sender, args) =>
	{
		if (args.IsAuthenticated)
		{
			// Save the account for the future
			store.Save (args.Account, "google");
			RunOnUiThread (showTasks);
		}
		else // Authentication failed
			Toast.MakeText (this, "Error logging in", ToastLength.Long).Show();
	};

	Intent authIntent = this.auth.GetUI (this);
	StartActivity (authIntent);
}

Intent loginIntent = auth.GetUI (this);
StartActivity (loginIntent);