How to use an Iframe Login to hide certain pages from users that are not logged in

Working on a project in wordpress, some pages run on iframes that come from a different login they provided me an iframe script to use.

<script src='https://batouwe.e-golf4u.nl/leden/iframe/js/resizehandler.js'></script>
<iframe id='egolf4u_iframe' frameborder='0' src='https://batouwe.e-golf4u.nl/leden/iframe/wedstrijd' style='width: 100%;'></iframe>
<script>
  jQuery('#egolf4u_iframe').on("load", function() {
        jQuery('#egolf4u_iframe').height(function (index, height) {
            return (height + 40);
        });
  });
</script>

we have some pages that they generate the data too and also the login form so the users can see the data (the users have an existing account with the iframe provider, they appear to have an auth key on the client side sinds users can switch to different iframes and not have to login again.

My question is i want to be able to lock not logined users from certain pages on the client side aswel. how do i do this. is it possible to edit the iframe script to change a certain block to hidden when they are not logged in and to visable when they are logged in.

the site is https://debatouwe.yeps.site/

if you want to see what i mean,

Any help appreaciated this is a project for school and it needs to be done asap this is all that im missing!

for users not to be able to access certain client side pages while logged into the iframe api login