Sign up not completed when I log to an app using apple id. What should i do?

Is there any documentation about the server to server notification, specifically what sort of data Apple servers send to our server when there is an update to users who used Sign in with Apple?

Running the sample "Juice" app, which demos the Sign In With Apple flow, doesn't seem to work with Xcode 12 beta and iOS 14 beta on the simulator (worked fine on the non-beta versions and on a real device with iOS 14 beta). Once the password for the device's Apple ID is entered, the wheel in the password field just keeps spinning. No error messages and nothing handed back over to the app from the ASAuthorizationController. Anyone else seeing this problem ? Are there any workarounds ?