@abc.abstractmethod<EOL><INDENT>def get_agents_by_query(self, agent_query):<DEDENT>
return<EOL>
Gets a list of ``Agents`` matching the given agent query.

        :param agent_query: the agent query
        :type agent_query: ``osid.authentication.AgentQuery``
        :return: the returned ``AgentList``
        :rtype: ``osid.authentication.AgentList``
        :raise: ``NullArgument`` -- ``agent_query`` is ``null``
        :raise: ``OperationFailed`` -- unable to complete request
        :raise: ``PermissionDenied`` -- authorization failure
        :raise: ``Unsupported`` -- ``agent_query`` is not of this service

        *compliance: mandatory -- This method must be implemented.*