Sign in with Apple is a single sign-on service offered natively on all Apple devices that gives users the option to register with apps using a randomly generated and unique email address.
A single sign-on service (SSO) allows users to authenticate with multiple platforms or services using a single set of credentials. Popular examples of SSOs include Facebook Login or Google Sign-In.
Unlike other SSO solutions that reveal a user's email address, Sign in with Apple provides an option to "hide" a user's personal email address from app developers. Hiding a personal email address is the killer privacy feature of Sign in with Apple.
Unfortunately, this killer feature may also kill personalized advertising on Apple devices and the web.
What is Sign in with Apple?
In September of 2019, Apple announced that they would require Sign in with Apple if an app offers a third-party SSO service such as Facebook Login or Google Sign-In. This new requirement immediately gave Sign in with Apple a sizeable footprint on iOS apps that would eventually equal all other third-party login services.