Give the caddy binary the ability to bind to privileged ports (e.g. 80, 443) as a non-root user:
sudo setcap 'cap_net_bind_service=+ep' /usr/local/bin/caddy
There isn't. There's a port of authbind, but I don't think anyone was able to get it working with caddy. The only solution I've heard of working is using the pf firewall to port forward, for example, 8080 to 80. Like this: https://salferrarello.com/mac-pfctl-port-forwarding/
