Example golang proxy script

I'm looking into the amppackager to see if I can get signed exchanges going for a project with static html files. I am able to use amppackager locally over port 8080.

To do test on a cloud server (with Go) I was hoping to also find an example script that would show how to proxy (locally) requests correctly. I'm not well versed in Go, so having this should help out tremendously.

request -> server <-> *index.go*

Are there any resources for this? I found this but sure stuff is missing (correct vary header, etc.)
> https://github.com/ampproject/amp-by-example/blob/master/backend/packager.go

Start by reviewing amppackager's local proxy behavior and the referenced backend/packager.go example from amp-by-example. Determine which request and response details, including the correct Vary header, the proposed index.go example must demonstrate. Done means a documented Go proxy example that shows how to forward requests correctly for cloud-server testing.

Written by the indexing model from the issue text.