def match_owner(self, url):
        """
        Finds the first entity, with keys in the key jar, with an
        identifier that matches the given URL. The match is a leading
        substring match.

        :param url: A URL
        :return: An issue entity ID that exists in the Key jar
        """
        for owner in self.issuer_keys.keys():
            if owner.startswith(url):
                return owner

        raise KeyError("No keys for '{}' in this keyjar".format(url))
Finds the first entity, with keys in the key jar, with an
        identifier that matches the given URL. The match is a leading
        substring match.

        :param url: A URL
        :return: An issue entity ID that exists in the Key jar