Feature request: Add explicit HTTP/2 / HTTP/1.1 negotiation logging in tsdproxy

[jlpnea]

First of all, thank you for developing and maintaining tsdproxy — it’s a very useful tool for reverse proxying in Tailscale environments.

I am currently using tsdproxy v2 as a frontend proxy terminating TLS for a Nextcloud Docker instance on a Synology NAS. I have configured tsdproxy with HTTPS termination, but Nextcloud and browser developer tools show that HTTP/1.1 is being used instead of HTTP/2 or HTTP/3. I have the same problem with onlyoffice Docker, only http/1.1 is used

When enabling log.level: debug, I was hoping to find explicit logs about the HTTP protocol negotiation (HTTP/1.1 vs HTTP/2) or ALPN during the TLS handshake to help debug why HTTP/2 is not negotiated. However, I cannot find any mention in the logs of HTTP versions negotiated or ALPN protocol announcements.

Could you consider adding detailed logging about HTTP protocol negotiation (including ALPN results) to help users diagnose these issues more easily?

This would greatly help to confirm whether tsdproxy properly negotiates HTTP/2 or HTTP/3 at the TLS layer in production setups.

Thank you very much for your work and support.

Best regards,
Jean-Louis