'Retrieve the NACL verification key for a given server for the given
key_ids
Args:
server_name (str): The name of the server.
key_ids (iterable[str]): key_ids to try and look up.
Returns:
Deferred: resolves to dict[str, VerifyKey]: map from
key_id to verification key.'

@defer.inlineCallbacks
def get_server_verify_keys(self, server_name, key_ids):

    keys = {}
    for key_id in key_ids:
        key = (yield self._get_server_verify_key(server_name, key_id))
        if key:
            keys[key_id] = key
    defer.returnValue(keys)
