Apps will get the best AutoFill experience when using Associated Domains with the webcredentials
association and properly annotating the textContentType
on any text fields. It's not necessary for your website to have a sign in form for you to set up Associated Domains with your app.
You can further streamline the experience by adopting ASAuthorizationController. This will allow your app to present a system sheet to offer a user's existing passwords (as well as passkeys) for signing in, if they have any. If they don't have any saved credentials, ASAuthorizationController silently returns an error and you can present your normal sign in form.