I learned through support, that Miro currently does not render pages from URLs that require a login. E.g. LinkedIn profiles, that were set to non-public, which you can see in your browser, but Miro fails to resolve.
The same would be true for any page that requires a login, like anything a user might have in their Intranet. According to Miro support, “this is indeed not possible (neither with the Web Page Capture feature, or the Miro Web Clipper)”
I’d like to suggest an enhancement, where links can be embedded and are rendered with the user’s credentials (if they are willing to supply them, of course).