def _get_first_urn(self, urn):
        """ Provisional route for GetFirstUrn request

        :param urn: URN to filter the resource
        :param inv: Inventory Identifier
        :return: GetFirstUrn response
        """
        urn = URN(urn)
        subreference = None
        textId = urn.upTo(URN.NO_PASSAGE)
        if urn.reference is not None:
            subreference = str(urn.reference)
        firstId = self.resolver.getTextualNode(textId=textId, subreference=subreference).firstId
        r = render_template(
            "cts/GetFirstUrn.xml",
            firstId=firstId,
            full_urn=textId,
            request_urn=str(urn)
        )
        return r, 200, {"content-type": "application/xml"}
Provisional route for GetFirstUrn request

        :param urn: URN to filter the resource
        :param inv: Inventory Identifier
        :return: GetFirstUrn response