var servletbase = "https://ricariche.setaweb.it:443/spidbutton/";
var canvas = "spidbuttoncanvas";

function CARTScript(src) {
	if (src!=null && src!=="")
    	document.write('<script src="' + src + '" type="text/javascript"></script>');
}
function CARTStyle(href) {
	if (href!=null && href!=="")
    	document.write('<link rel="stylesheet" type="text/css" href="' + href + '">');
}

<!-- JQUERY -->
CARTScript("");

<!-- SPID SMART BUTTON  -->
CARTScript("https://ricariche.setaweb.it:443/spidbutton/spidsmartbutton/js/spid-button.js");
CARTScript("https://ricariche.setaweb.it:443/spidbutton/spidsmartbutton/js/providers.js");
CARTScript("https://ricariche.setaweb.it:443/spidbutton/spidsmartbutton/js/i18n.js");
CARTScript("https://ricariche.setaweb.it:443/spidbutton/spidsmartbutton/js/config.js");

<!-- Font awsome -->
CARTStyle("//cdnjs.cloudflare.com/ajax/libs/font-awesome/5.15.3/css/all.min.css");

<!-- popup modale  -->
CARTStyle("https://ricariche.setaweb.it:443/spidbutton/css/modal.css");

<!-- matteo 13/04/2021 -->
<!-- per sapere in modo dinamico dove atterrare al termine -->
<!-- del pagamento, usiamo i cookie per salvare la url corrente -->
<!-- dove è incluso il plugin -->
<!-- il domain del cookie deve essere il root domain -->
document.cookie = "spidbutton-hostpage=" + encodeURIComponent(window.location.href) + ";domain=setaweb.it;path=/";

<!-- questo codice inserisce il plugin (web.html) nel div del chiamante -->
document.write('<script type="text/javascript">$(document).ready(function(){$("#' + canvas + '").load("https://ricariche.setaweb.it:443/spidbutton/spid.web.html");});</script>');