Again, possession or control of the Private Key is not required for a CA to issue a SSL Certificate. The BR requirements for a subscriber's Private Key are essentially limited to knowledge of (i) the key being compromised or (ii) the key being likely to be compromised. There are some additional restrictions on Public Key sizes and validation.
The BR requires:
- proof of control over the domain
- technical requirements on the public key
- security measures around the private key
A CA can, and several have, issue certificates without utilizing a CSR or Private Key. Subscribers and CAs do not have to prove control over a Private Key, they must simply attest the key's security complies with the BR.
Reference the discussion starting here (it was @petercooperjr):
I'm not sure if they do or not, but ISRG staff noted that most HSMs support signing a CSR. I know I'm making some assumptions here, but IMHO the knowledge HSMs being capable of this would likely have influenced design decisions to potentially support that in the future (if not initially).
Yes. I eventually found your post and linked to it above. You were the person who discovered that discussion and shared it with this community, and I wanted to credit you for that.