Embedded Page Personalisation

Hi,

Would it be possible to personalised the default success or error page ?

```

Authorization successful.

Application has successfully obtained access credentials

This window can be closed now.

```

Also, displaying am personalised "error page" could be great, instead of a 500 error with no message to users and outside our app.

Thank you for this package and your consideration.

Regards

> // TODO: We could introduce a user-defined redirect page.
Just saw the comment, it's a good idea 👍 😆