I'm quite new to Xamarin development and have what is likely a very simple problem. I'd like the first thing to happen in my app to be a login. The login is pretty much exactly the same as the "Web Authenticator" sample in the Xamarin Essentials samples. However, it's the flow that I'm struggling to figure out. I'd like that to be the entry point of my app. Upon successful login, the rest of the app becomes usable. However, if login fails, I'd like to display a "retry or exit". In other words, I'd display the login page first, and only display the main page upon successful login, and exiting the app without it.
Whereas it embarrasses me to ask such a trivial question, doing so might save me a lot of time and end up with a better solution than if I just grind my way through it. So, good instructions or a code example would be much appreciated.
Note that initially this is just for Android, but I'd like to do the same with the iOS and UWP versions eventually.