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
        """
        if isinstance(request, etree._Element):
            elem = request
        else:
            if isinstance(request, Document):
                request = request.toxml()
            elem = fromstring(request, forbid_dtd=True)

        session_indexes = []
        session_index_nodes = OneLogin_Saml2_Utils.query(elem, '/samlp:LogoutRequest/samlp:SessionIndex')
        for session_index_node in session_index_nodes:
            session_indexes.append(OneLogin_Saml2_Utils.element_text(session_index_node))
        return session_indexes