[nybble41]

> It seems pretty different from a password because you're not giving control of your domain: if they broke their contract, you could take it back at any time.

You are giving them everything they'd need to obtain a DV certificate for your domain, though. You can stop them from using it at any time just by changing the DNS records, but you'd need to wait at least two years (825 days for maximum TLS certificate duration) before you could be certain any certificates they had been issued before that point had expired.