[timdorr]

How will this work for apps that depend on the third party for more than just identity? For instance, does an app built on Spotify's API have to include a Sign in with Apple option? Or something like CI2Go, which is an app for CircleCI, which only offers log in via GitHub or Bitbucket.

I have to assume there will be exceptions.

[icebraining]

If you are built on Spotify, then the use is not signing in to your app, but to Spotify (and then authorizing your app), so it should be up to them to provide the Apple Sign In feature, I assume.