touch-id-5.swift

func requestFingerprintAuthentication() {
    let context = LAContext()
    var authError: NSError?
    let authenticationReason: String = "To display a message to the user"
    
    if context.canEvaluatePolicy(LAPolicy.DeviceOwnerAuthenticationWithBiometrics, error: &authError) {
        context.evaluatePolicy(LAPolicy.DeviceOwnerAuthenticationWithBiometrics, localizedReason: authenticationReason, reply: {
            (success: Bool, error: NSError?) -> Void in
            if success {
                self.updateMessageLabel("Woohoo")
            } else {
                self.updateMessageLabel("Unable to Authenticate")
            }
        })
    }
}

func updateMessageLabel(message: String) {
    dispatch_async(dispatch_get_main_queue(), {
        self.messageLabel.text = message
    })
}