Function hosted_by 

fn hosted_by(subject: &str, server: &str) -> bool

Whether subject is an account on the server server names: both are did:web, and the subject’s hostname sits strictly below the server’s.

describeServer at a host’s hostname answers with the DID of the PDS serving it, never the host’s own, so for a host the two reads agree when the server describing itself is the one the host’s name is under. The same consistency check as for a server, read across a zone rather than an exact match.