For those unfamiliar, “Sign in with Apple” was designed to be a privacy-oriented alternative to signing in with Facebook and Google. This is because when choosing to sign in with Apple, users have the option of using a throwaway email, created by Apple, instead of having to hand over their personal email to the website or service they’re signing up for. This is versus signing in with Facebook or Google where more identifiable information is available.
Apple also made it a requirement where if an app/service on iOS or Mac offers users to sign in with Facebook or Google, they must offer “Sign in with Apple” as an alternative. This is the reason why the antitrust complaint has been filed, and why the US Department of Justice is investigating the matter.
While some have praised the feature, some developers feel that making it mandatory means that they will get cut off from access to information from their customers, and that it was Apple’s way of exerting control over its mobile devices. Whether or not this investigation will lead to anything remains to be seen.