Gets the SessionIndexes from the Logout Request
        :param request: Logout Request Message
        :type request: string|DOMDocument
        :return: The SessionIndex value
        :rtype: list

def get_session_indexes(request):
        """
        Gets the SessionIndexes from the Logout Request
        :param request: Logout Request Message
        :type request: string|DOMDocument
        :return: The SessionIndex value
        :rtype: list
        """

        elem = OneLogin_Saml2_XML.to_etree(request)
        session_indexes = []
        session_index_nodes = OneLogin_Saml2_XML.query(elem, '/samlp:LogoutRequest/samlp:SessionIndex')
        for session_index_node in session_index_nodes:
            session_indexes.append(OneLogin_Saml2_XML.element_text(session_index_node))
        return session_indexes