In-Memory Caching

// Cached token between requests
let token;

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

async function handleRequest(request) {
  // If the token is not set yet, get one
  if (!token) {
    try {
      await fetchAndSetToken();
    } catch (e) {
      return new Response("Failed to get token", {
        status: 500
      });
    }
  }

  // Get stackId and siteId from request search
  const url = new URL(request.url);
  const stackId = url.searchParams.get("stackId");
  const siteId = url.searchParams.get("siteId");

  // See https://developer.stackpath.com/en/api/cdn/#operation/GetSiteScripts
  return fetch(
    `https://gateway.stackpath.com/cdn/v1/stacks/${stackId}/sites/${siteId}/scripts`,
    {
      headers: { authorization: token }
    }
  );
}

// See https://developer.stackpath.com/docs/en/getting-started/
const CLIENT_ID = "CLIENT_ID";
const CLIENT_SECRET = "CLIENT_SECRET";

// Create an oauth token and set the token variable
async function fetchAndSetToken() {
  let tokenResp = await fetch(
    "https://gateway.stackpath.com/identity/v1/oauth2/token",
    {
      method: "POST",
      body: JSON.stringify({
        client_id: CLIENT_ID,
        client_secret: CLIENT_SECRET,
        grant_type: "client_credentials"
      }),
      headers: {
        "Content-Type": "application/json"
      }
    }
  );

  // Leave token as is if another request fetched it at the same time and finished first
  if (!token) {
    if (!tokenResp.ok) {
      throw new Error("Failed to retrieve token");
    }

    const { token_type, access_token, expires_in } = await tokenResp.json();
    token = `${token_type} ${access_token}`;

    // Get a new token a minute before the current token is set to expire
    setTimeout(() => {
      fetchAndSetToken();
    }, Math.max(expires_in * 1000 - 60000, 0));
  }
}