givenName property
The users given name, in case it was requested. You will need to provide the AppleIDAuthorizationScopes.fullName scope to the AppleIDAuthorizationRequest for requesting this information.
This information will only be provided on the first authorizations. Upon further authorizations, you will only get the userIdentifier, meaning you will need to store this data securely on your servers. For more information see: https://forums.developer.apple.com/thread/121496
Implementation
final String? givenName;