Function confirm_with 

pub async fn confirm_with<F, Fut>(
    address: &Address,
    actor: &str,
    lookup: F,
) -> Result<Resolved, ResolveError>
where
    F: FnMut(&Address) -> Fut,
    Fut: Future<Output = Result<Found, FetchError>>,

Confirm that address names actor, as Mastodon’s ProcessAccountService#check_webfinger! does before it believes an actor’s handle: resolve_with, and the actor the canonical handle’s answer names has to be actor. Returns what it resolved to, whose address is the handle to show.

A subject is read as check_webfinger! reads it, by its first two parts split at @, so acct:alice@social.example@elsewhere is alice@social.example; resolve_with refuses it, as ResolveAccountService does.

Errors

As resolve_with, and when the handle names another actor.