Auth with headers

Allow or deny a request based on a known pre-shared key in a header. This is not meant to replace the WebCrypto API.

/**
 * @param {string} PRESHARED_AUTH_HEADER_KEY Custom header to check for key
 * @param {string} PRESHARED_AUTH_HEADER_VALUE Hard coded key value
 */
const PRESHARED_AUTH_HEADER_KEY = 'X-Custom-PSK';
const PRESHARED_AUTH_HEADER_VALUE = 'mypresharedkey';

async function handleRequest(request) {
  const psk = request.headers.get(PRESHARED_AUTH_HEADER_KEY);

  if (psk === PRESHARED_AUTH_HEADER_VALUE) {
    // Correct preshared header key supplied. Fetch request from origin.
    return fetch(request);
  }

  // Incorrect key supplied. Reject the request.
  return new Response('Sorry, you have supplied an invalid key.', {
    status: 403,
  });
}

addEventListener('fetch', event => {
  event.respondWith(handleRequest(event.request));
});