Alternatively, with Caddy (with automated TLS, single static binary): example.com { handle /ip { header Content-Type application/json

Alternatively, with Caddy (with automated TLS, single static binary): example.com { handle /ip { header Content-Type application/json respond `{"host":"{host}","ip":"{remote_host}","port":"{remote_port}"}` } } Though the usefulness of the host (client specified it), remote port (it's random), and server ip/port (it's static and not useful for the client) are questionable.