Iframes is how you embed content from other sites. It might not be a pure as writing everything in go;) but it’s something anyone can do since you just paste in some code to a html file. It is also used by Vimeo and SoundCloud. But I’m away that there might be some XSS issues. What other option do you have in mind? Something like the Twitter cards just the other way around could do the trick and most big tech sites offer this preview text and image