Authentication Implement authentication flows on iOS using the AuthenticationServices framework, including Sign in with Apple, passkeys, OAuth/third-party web auth, Password AutoFill, and biometric re-authentication. Contents - Sign in with Apple - Credential Handling - Credential State Checking - Token Validation - Existing Account Setup Flows - Passkeys - ASWebAuthenticationSession (OAuth) - Password AutoFill Credentials - Biometric Authentication - Security Boundaries - SwiftUI SignInWithAppleButton - Common Mistakes - Review Checklist - References Sign in with Apple Add the "Sign in with…