Handle CORS (OPTIONS request) in Edge Lambda for AWS CloudFront

handleCorsForCloudFront.js

function checkOrigin(origin) {
  if (!origin) {
    return false;
  }
  const [protocol, host, port] = origin.split(':');
  // TODO: put your own logic here
  if (!host) {
    return false;
  }
  if (host === '//localhost') {
    return true;
  }
  if (host === '//127.0.0.1') {
    return true;
  }
  if (host === '//0.0.0.0') {
    return true;
  }
  return false;
}

exports.handler = (event, context, callback) => {
  const request = event.Records[0].cf.request;
  const headers = request.headers;

  if (request.method === 'OPTIONS') {
    const origin = headers.origin && headers.origin[0] && headers.origin[0].value;
    const response = checkOrigin(origin) ? {
      status: '204',
      headers: {
        'access-control-allow-origin': 
          [{ key: 'Access-Control-Allow-Origin', value: origin}],
        'access-control-allow-headers': // TODO: add any other headers that your app is using
          [{ key: 'Access-Control-Allow-Headers', value: 'Content-Type'}], 
        'access-control-allow-methods': // TODO: restrict your methods
          [{ key: 'Access-Control-Allow-Methods', value: 'GET, HEAD, PUT, POST, DELETE, PATCH'}],
        'access-control-allow-credentials': 
          [{ key: 'Access-Control-Allow-Credentials', value: 'true'}],
        'access-control-max-age': // TODO: tune your expiry
          [{ key: 'Access-Control-Max-Age', value: '8640000'}],
      },
    } : {
      status: '401',
    };
    callback(null, response);
  }
  else {
    callback(null, request);
  }
};