To that point, I think a lot in this community (myself included) hear a lot more about reverse proxies (nginx, etc.) than regular proxies.
Is there a well-behaving proxy that could this behavior our of the box, and is easy-to-integrate and actively maintained? (For instance, something that I could set as the proxy for my entire backend process with an environment variable, and it would pass through everything except github.com requests? Configurable cache time overrides on a per-domain basis?)
I've seen Squid mentioned as a popular proxy - is this a use case it's intended to address?