Curtis Herbert on integrating iOS 13's new Sign in with Apple feature:
As I worked, though, one thing I kept hearing from anyone doing the same is "oh, boy, did you manage to find any documentation??" The WWDC videos are great primers on how to get the iOS UI to do its thing, but there's a lot of details about what you as a developer should do after the sign in that'll inform how you integrate this new API.
It is disturbing how poor Apple's official documentation has become. Back in the iOS 2-5 days I used them as the gold standard for how to write technical documentation. But now they seem to be constantly chasing major iOS releases such that they cannot or will not write sufficient documentation.
In the future, when I need to integrate Sign In with Apple into my apps, my first stop will not be Apple's documentation but this fantastic article by Chris.