Caddyfile

# /etc/caddy/Caddyfile

{
    auto_https disable_redirects
}

:80 {
    respond "Hello from HTTP port 80"
}

localhost {
    respond "Hello from localhost HTTPS (trusted)"
}

1.2.3.4:443 {
    tls internal
    respond "Hello from 1.2.3.4 HTTPS (self-signed)"
}

Install caddy per https://caddyserver.com/docs/install then run the following:

# copy the gist contents
sudo vim /etc/caddy/Caddyfile

# validate config
caddy validate --config /etc/caddy/Caddyfile

# install self-signed certs from caddy's internal CA
sudo caddy trust

# verify they were created
sudo find /var/lib/caddy -name "*.crt" -o -name "*.pem" 2>/dev/null

# reload caddy service
sudo systemctl reload caddy