In order to use Sign in with Apple, you need to have an developer account. Currently the Apple Developer program is $99 a year. Once you signup for the Apple Developer program, you can follow this tutorial on how to install Sign in with Apple on the web (Shopify). I know I didn’t fully answer your question, but this is a great starting point! Hopefully Apple and Shopify will team up in the future to make an App for easy integration!
Social Login is a single sign-on for end users. Using existing login information from a social networking app the user can sign in to a third party website instead of creating a new account specifically for that website. This simplifies registrations and logins for end users.
Sign in with Apple is the fast, easy, and more private way to sign in to third-party apps and websites using the Apple ID that you already have.
You can use Shopify Social login by miniOrange App in which you can integrate any Apple ID social network application with Access richer user profiles such as Name, E-mail, User ID, and more in a cost-efficient way.