Function is_identity_denied_by 

pub fn is_identity_denied_by(
    allowed: &[String],
    identities: &[&str],
    match_fn: impl Fn(&str, &str) -> bool,
) -> bool

Whether any identifier of one account is explicitly denied, independent of any grant.

Needed by channels that accept more than one identifier for the same account. Asking is_user_allowed_by per identifier is not sufficient there: a deny on one alias is defeated by a wildcard grant reached through another, so the sender has to be rejected when any of its identifiers is denied.