Iframe not loading URLs inside the CEP panel

Hello Everyone,
I am trying to display a URL in the CEP panel and authenticate it. I attempted to use an Iframe in the CEP panel to show the URL, but it does not appear in the panel. Is there a restriction on the URL that prevents it from being embedded in the Iframe? Unfortunately, I am unable to share the URL at this time. Apologies for any inconvenience.
I want to show the respective URLs in the panel as well as need to authenticate and redirect into another page.