Using custom key/cert auth as part of fetch request

I am writing a worker that needs to call fetch into an external service. This service is authenticated using a custom key/cert (mTLS). On AWS Lambda, I implemented it like this:

  var options = {
    hostname: 'HOSTNAME_HERE',
    port: 443,
    path: path,
    method: 'GET',
    key: key,
    cert: cert,
const req = https.get(
      res => {})

It could also be implemented with fetch by including a custom agent into the fetch options.

How can I do the above using the fetch implemented in the worker? As far as I can tell it is not possible to include a custom agent?

Just saw this:
Is there any update on if the roadmap/timeline (or lack thereof) has changed since January?