You already proved that you have access to it. Why is that no question asked? Normal DV certs are either "add a CNAME, upload a uniquely named html / txt file,

You already proved that you have access to it. Why is that no question asked? Normal DV certs are either "add a CNAME, upload a uniquely named html / txt file, or click a link in an email" -- you've already done one of those (automatically in caddy)