Just wanted to mention here that this plugin will no longer be needed because of the work done in caddyserver/caddy#5104.

The real client IP will be parsed if trusted_proxies is configured in global options, and the header it's read from can be configured with client_ip_headers (defaulting to X-Forwarded-For). The logs will include it as a new client_ip field.

Compared to this plugin, this approach doesn't affect req.RemoteAddr, that's left intact, but any other modules/handlers that might care to get the real client IP can get it from the request context.