@abc.abstractmethod<EOL><INDENT>def get_proxy_session(self):<DEDENT>
return<EOL>
Gets a ``ProxySession`` which is responsible for acquiring authentication credentials on behalf of a service client.

        :return: a proxy session for this service
        :rtype: ``osid.proxy.ProxySession``
        :raise: ``OperationFailed`` -- unable to complete request
        :raise: ``Unimplemented`` -- ``supports_proxy()`` is ``false``

        *compliance: optional -- This method must be implemented if
        ``supports_proxy()`` is ``true``.*