Biometric authentication

Biometric authentication unlocks an app using the user's face or fingerprint instead of a password. The first time, the user opts in; after that, opening the app is one glance or one tap.

Always offer a password fallback for when biometrics fail (sunglasses, wet fingers) or are not enrolled. Never store the biometric data yourself — the operating system handles it. Treat biometrics as a convenience layer, not the only door.