Yesterday during its WWDC 2019 keynote, Apple announced iOS 13, which includes a new 'Sign in with Apple' feature. It's meant to provide an alternative to social media sign-in methods, such as Facebook and Google.
As it turns out, this will be a mandatory option for all apps that support third-party sign-in. Apple published its updates to App Store Review Guidelines, saying the following:
Sign In with Apple will be available for beta testing this summer. It will be required as an option for users in apps that support third-party sign-in when it is commercially available later this year.
With the way this is worded, it seems like the alternative that developers could use, if they really don't want to use Apple's feature, is to remove the other options from Facebook, Google, etc.
But 'Sign in with Apple' is meant to be more secure. It doesn't share your personal data with an app vendor like a third party might. It still might ask you to share your email, but if you choose to hide it. Apple will create a fake email address that will forward to your real one. Each app gets its own fake email address, so if you shut one down, it's gone for good.
The feature will go live this fall with iOS 13.