What is authentication?
Implement iOS authentication patterns including Sign in with Apple (ASAuthorizationAppleIDProvider, ASAuthorizationController, ASAuthorizationAppleIDCredential), credential state checking, identity token validation, ASWebAuthenticationSession for OAuth and third-party auth flows, ASAuthorizationPasswordProvider for AutoFill credential suggestions, and biometric authentication with LAContext. Use when implementing Sign in with Apple, handling Apple ID credentials, building OAuth login flows, integrating Password AutoFill, checking credential revocation state, or validating identity tokens server-side. Source: dpearson2699/swift-ios-skills.