Any mobile app that uses a third-party login must also offer Sign In With Apple in order to be approved for the App Store. Existing apps with third-party login must support Sign In With Apple by April 2020.
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4.8 Sign in with Apple
Apps that exclusively use a third-party or social login service (such as Facebook Login, Google Sign-In, Sign in with Twitter, Sign In with LinkedIn, Login with Amazon, or WeChat Login) to set up or authenticate the user’s primary account with the app must also offer Sign in with Apple as an equivalent option. A user’s primary account is the account they establish with your app for the purposes of identifying themselves, signing in, and accessing your features and associated services.