Comment by maxgashkov
2 hours ago
Webserver control is never used and must not be used to prove domain ownership. If you're pwned and have to re-point to a server stood up from backup, having registrar relying on someone being able to put up a random file on a compromised machine would be a total security disaster.
On a different note, adding a file on webserver is one of the ACME methods (HTTP-01) to get a SSL/TLS certificate so it is indeed considered as possession method in real world already
You're missing that HTTP-01 challenge grants you no ability beyond what the check has demonstrated, i.e. you have proven that you're able to serve random file from a webserver, so the grant is to allow you to serve them via TLS connection.
There are no comparable _technical_ proof-of-registration methods because all of them would require actual access to registrar control panel and be outright silly ('point the domain to a random nameserver').
So no, proper registrars never use webserver control as means to prove identity or ownership.
To clarify, my observation is around how it might have happened, not if this is the right way to do it