'Retrieve identity / authentication class instance.
:rtype: :class:`OpenStackIdentityConnection`'

def get_auth_class(self):

    if (not self._osa):
        auth_url = self._get_auth_url()
        cls = get_class_for_auth_version(auth_version=self._auth_version)
        self._osa = cls(auth_url=auth_url, user_id=self.user_id, key=self.key, tenant_name=self._ex_tenant_name, domain_name=self._ex_domain_name, token_scope=self._ex_token_scope, timeout=self.timeout, parent_conn=self)
    return self._osa
