[Enhancement] Allow injecting the Parent Activity/Window in the Client Builder

Description

The UI Parent (Window on UWP/Activity on Android) should be injected at the Client Application Builder level and not be required at the AcquireTokenInteractiveParameterBuilder level.

Current 3.0 API

var pca = PublicClientApplicationBuilder.Create(options.ClientId)
                                        .WithB2CAuthority(authority)
                                        .Build();

var result = await pca.AcquireTokenInteractive(Scopes)
                      .WithParentActivityOrWindow(Parent)
                      .ExecuteAsync();

Expected 3.0 API

var pca = PublicClientApplicationBuilder.Create(options.ClientId)
                                        .WithB2CAuthority(authority)
                                        .WithParentActivityOrWindow(Parent)
                                        .Build();

var result = await pca.AcquireTokenInteractive(Scopes)
                      .ExecuteAsync();

[HappyNomad]

I’m in favor of the WithParentActivityOrWindow method going away. My auth code is in the view-model. Regardless of possible trickery for obtaining the window reference there, I’m opposed to view objects even passing through that layer.

[dansiegel]

I would say this perhaps relates to #1104 since both these issues are around the ParentActivityOrWindow. The more I think about it, the more I’m thinking that perhaps we’re looking at the entirely wrong places. Perhaps this could all be simplified with a platform specific activity ONLY on those platforms where there is such a need.

public static class MSALActivityLocator
{
    public static Activity CurrentActivity { get; set; }
}

[Application]
class App : Application, Application.IActivityLifecycleCallbacks
{
    public void OnActivityCreated(Activity activity, Bundle savedInstanceState)
    {
        MSALActivityLocator.CurrentActivity = activity;
    }
}

Alternatively you could do what I do personally and take a dependency on Plugin.CurrentActivity. The benefit here, is that you’re not introducing a new API, and using a dependency most Xamarin.Android developers are already used to using.

[Application]
class App : Application, Application.IActivityLifecycleCallbacks
{
    public void OnActivityCreated(Activity activity, Bundle savedInstanceState)
    {
        CrossCurrentActivity.Current.Activity = activity;
    }
}

// Alternatively:
public class MainActivity : FormsAppCompatActivity
{
    protected override void OnCreate(Bundle bundle)
    {
        CrossCurrentActivity.Current.Activity = this;
    }
}