iOS Application login via SFSafariViewController

Question

I'm looking to replicate the login behaviour of Amazon's AWS Console ios application (https://apps.apple.com/us/app/aws-console/id580990573).

The basics are that when you open the app, you are then shown the typical login page as you would if you are logging into the AWS Console in a regular web browser. However, after logging in correctly, the Safari Web Controller "magically" disappears and you are logged in.

I would imagine this is some sort of session, possibly a cookie that is set, either way I want to also perform my login in the SFSafariViewController, but because there is almost no link between the web controller and the application initiating it, how do you "hand over" or "parse", or "give" the parent application the token, or auth, or whatever information you need to parse it.

So far I have tried to monitor the redirects with:

extension ViewController: SFSafariViewControllerDelegate{
    func safariViewController(_ controller: SFSafariViewController, initialLoadDidRedirectTo URL: URL) {
        print("initialLoadDidRedirectTo: \(URL.absoluteString)")
}
}

This works only if it has a single redirect initialLoadDidRedirectTo. So if you have to do something like sign up, or anything else it doesn't fire after the first redirect.

What's the reliable way to let my application know that my user has successfully logged in using a SFSafariViewController that I present within my application?

Note: I have full control of the login start and complete pages, and can run any javascript etc within these pages.