There is a standard for this. It's called oEmbed: https://oembed.com/ https://oembed.com/ The chat host still likely needs access to the "non-public website" t

There is a standard for this. It's called oEmbed: https://oembed.com/ https://oembed.com/ The chat host still likely needs access to the "non-public website" to discover and call its oEmbed API, so that's something you'd have to figure out, but any website anywhere can offer oEmbed metadata if it wishes.