Parts, the modified Listener, has not been open sourced. Caddy's author was quick to deflect and squash any discussion about what else is held private.

The easiest answer would have been a "sure, here's the link". Instead the thread has been locked for being off-topic, yet the original issue and the question concern the same thing.

As someone who is working on Caddy, I can assure you that Caddy is still very much open source! mholt and I have been working on version 2 which has a lot of improvements over the first version of Caddy. It's not in a releasable state yet.

We are currently at a stage where we are getting feedback from the community on our current progress. If you want to be a part of that, feel free to reach out to one of us.

Caddy 2 is under internal development, and will be open source as per https://caddyserver.com/blog/announcing-caddy-1_0-caddy-2-ca... Ofc, the thread has been locked, because it is off-topic, the linked issue is about listeners, not the development of Caddy 2.