I understand that https is enabled by default and i think i managed to set up the caddyfile in a way that this is enabled: https://caddyserver.com/docs/automatic-https
what i don't understand is how i configure the certificate to use. the documentation is very vague about that (https://caddyserver.com/docs/automatic-https), but i don't think caddy issues a valid let's encrypt certificate automatically.
This is not possible. Caddy only supports self signed certificates.