Cloudflare JWT decoding worker

cloudflare_decode_jwt.js

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

async function handleRequest(request) {
  
  const token = getJwt(request)
  
  const payload = get_payload(token)

  const json = JSON.stringify(payload, null, 2)

  return new Response(json, {
      headers: {
        "content-type": "application/json;charset=UTF-8"
      }
    })
}

function get_payload(token) {
  let p;
  if (token == null) {
    p = null;
  } else {
    p = decodeJwt(token);
  }
  return p;
}

function getJwt(request) {
  const authHeader = request.headers.get('Authorization');
  if (!authHeader || authHeader.substring(0, 6) !== 'Bearer') {
    return null
  }
  return authHeader.substring(6).trim()
}

function decodeJwt(token) {
  const parts = token.split('.');
  const header = JSON.parse(atob(parts[0]));
  const payload = JSON.parse(atob(parts[1]));
  const signature = atob(parts[2].replace(/_/g, '/').replace(/-/g, '+'));
  return {
    payload: payload
  }
}