var targetOP = "https://oa.dnc.global";
    function check_session() {
               var client = "<id_du_client>";  // ID du client (client_id) enregistré sur le serveur
               var sessionState = $COOKIES["session_state"];
               var mes = client + " " + sessionState;
               var iframe = window.parent.document.getElementById ("iframeOP");
               iframe.contentWindow.postMessage (mes, targetOP);
    }