MacRumors:

Apple in iOS 13 introduced a new Sign in with Apple feature, which is designed to let you create accounts for apps and websites using your Apple ID, so you don’t have to give away your personal information.

Sign in with Apple is an alternative to the existing sign in with Google and Facebook options that apps and websites often offer. Apple’s version protects your privacy and even lets you mask your email address.

I’ve seen some developers complaining about having to implement this but any developer who doesn’t want to give users this option is one whose software I wouldn’t trust or use.