purging fetch cache that uses a custom cache key

// processes request to https://example.com/foo.json
export default {
  async fetch(request) {
    const url = new URL(request.url);
    const cacheKey = `https://${url.hostname}${url.pathname}`;

    const headers = new Headers(request.headers);
    headers.set("x-foo", url.host);

    # rewrite host so that we proxy to origin
    url.host = 'originserver.com'
    
    let response = await fetch(url.toString(), {
      cf: {
        cacheKey: cacheKey,
        cacheTtl: cacheTtlSec,
        cacheEverything: true,
        cacheTtlByStatus: {
          '100-199': 0,
          '200-299': cacheTtlSec,
          '300-599': 0,
        }
      },
      headers: headers,
    });
    response = new Response(response.body, response);
 
    return response;
  },
};

curl -s -X POST "https://api.cloudflare.com/client/v4/zones/xxx/purge_cache" -H "Authorization: Bearer xxx"  -H "Content-Type: application/json" -d '{"files":["https://originserver.com/foo.json"]}'

{"files":[{"url":"https://originserver.com/foo.json", "headers": {"x-foo": "example.com"}}]}