What’s your idea?
Please add support for Apple Sign in (single sign on service)
What problem might it solve?
Make it really easy and convenient to sign in on Apple devices. Especially with the latest additions introduced that allows sign in with touch-id and face-id on the web.
It also gives Apple users a way to sign in and be sure their privacy is respected.
Have you seen it somewhere else?
Starting to be more more common 
Any ideas on how you think it could/should work?
Apple developer has a guide on how to implement it. I assume it will be similar to how you already implemented Single-sign-on with Google & others.