touch-id-4.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 {
                dispatch_async(dispatch_get_main_queue(), {
                    self.messageLabel.text = "Woohoo"
                })
            } else {
                dispatch_async(dispatch_get_main_queue(), {
                    self.messageLabel.text = "Unable to Authenticate"
                })
            }
        })
    }
}