import LocalAuthentication

func afterUserAuthorized(perform handler: @escaping (Bool)->()) {
    let context = LAContext()
    var error:NSError?

    /* .deviceOwnerAuthentication - using Touch ID or the device password
     .deviceOwnerAuthenticationWithBiometrics - use Touch ID only */
    guard context.canEvaluatePolicy(.deviceOwnerAuthentication, error: &error) else {
        fatalError("No TouchID or passcode set on this device")
    }

    context.evaluatePolicy(.deviceOwnerAuthentication, localizedReason: "Please, pass authorisation to enter this area") { success, error in
        guard success else {
            print("Error: \(error)")
            /* where error can be one of: .authenticationFailed, .userCancel, .userFallback, .systemCancel,
             .passcodeNotSet, .touchIDNotAvailable, .touchIDNotEnrolled */
            handler(false)
            return
        }

        print("Hooray! User passed!")
        handler(true)
    }
}