Authentication

Covers the full iOS authentication stack: Sign in with Apple with ASAuthorizationController, OAuth flows via ASWebAuthenticationSession, Password AutoFill integration, and biometric auth with LAContext. The real value is in the credential handling details, like the critical gotcha that email and fullName are only provided on first authorization, so you must cache them immediately. Includes proper credential state checking patterns for detecting revoked access, server-side identity token validation workflows, and the credentialRevokedNotification observer you need to handle mid-session logouts. The examples show both UIKit and SwiftUI implementations with actual delegate code, not just conceptual patterns. Use this when you're implementing any modern iOS login flow and need to handle Apple's specific quirks around credential persistence and validation.