GCP Cloud Function CORS with Netlify.js

const netlifyHost = 'my-app.netlify.app';

const shouldAllowCORS = (origin) => {
  if (/http\:\/\/localhost:/.test(origin)) {
    return true;
  }
  if (origin === (`https://${netlifyHost}`) || (new RegExp(`--${netlifyHost.replace(/\./g, '\.')}`)).test(origin)) {
    return true;
  }
  return false;
}

/**
 * Responds to any HTTP request.
 *
 * @param {!express:Request} req HTTP request context.
 * @param {!express:Response} res HTTP response context.
 */
exports.myHandler = (req, res) => {
  const origin = req.headers.origin;
  if (shouldAllowCORS(origin)) {
    res.set('Access-Control-Allow-Origin', origin);
    if (req.method === 'OPTIONS') {
      res.set('Access-Control-Allow-Methods', 'POST');
      res.set('Access-Control-Allow-Headers', '*');
      res.status(204).send('');
      return;
    }
  }

  // ... rest of handler

};