why the header `mf-original-url` only exist when debugging a worker locally with wrangler? when i de

export default {
    async fetch(request, env: Env): Promise<Response>
    {

        request.headers.forEach((value, key) =>
        {
            console.log(key, value); // prints mf-original-url only locally 
        });

export default {
    async fetch(request, env: Env): Promise<Response>
    {

        request.headers.forEach((value, key) =>
        {
            console.log(key, value); // prints mf-original-url only locally 
        });