Do you have an app in the App Store for iPhone or iPad? Is your app using third party login mechanisms, like Facebook or Google? If so, it’s most likely that your app needs to be updated by next spring!
Apple recently released their own anonymous and private way to login to apps, “Sign in with Apple”. Apple has updated their App Store guidelines, mandating that this new login mechanism needs to be included among the other third-party logins in the future. So if you’re planning on developing new apps or are updating your existing ones, you should react to this rather sooner than later.
There are of course exceptions. If your app is only using proprietary username/password, has corporation/education account or uses a government or industry-backed citizen identification system, then this new login mechanism is not needed. There are a few other exceptions, and some corner cases that most probably will not be resolved before the new guidelines are active in April 2020.