This is how to authenticate a user with biometrics in swift

AuthenticationWithBiometrics.swift

import LocalAuthentication

class AuthenticationService {
    // We need to provide a FaceID description in info.plist:
    // Privacy - Face ID Usage Description -> Identify yourself!
    
    func authenticate() {
        let context = LAContext()
        var error: NSError?
        
        // In objc an inout parameter is known as Pointer that's why &error
        if context.canEvaluatePolicy(.deviceOwnerAuthenticationWithBiometrics, error: &error) {
            // Shown just for users with touch ID
            let reason = "Identify yourself!"
            
            context.evaluatePolicy(.deviceOwnerAuthenticationWithBiometrics, localizedReason: reason) { [weak self] success, authenticationError in
                DispatchQueue.main.async {
                    if success {
                        // Authentication succeeded
                    } else {
                        // Authentication failed
                    }
                }
            }
        } else {
            // Device Biometrics unavailable
        }
    }
}