The Open ID foundation published an open letter to Craig Federighi regarding Sign in With Apple. Although the foundation praised Apple for the initiative, it worries that it strays too far from Open ID and opens users to security and privacy risks.
The current set of differences between OpenID Connect and Sign In with Apple reduces the places where users can use Sign In with Apple and exposes them to greater security and privacy risks. It also places an unnecessary burden on developers of both OpenID Connect and Sign In with Apple. By closing the current gaps, Apple would be interoperable with widely-available OpenID Connect Relying Party software.