could we have some sort of Is-Autonomous header?

["Soni L." <[e-mail]>]

hello!

one of the issues with fediverse is how each instance caches other 
instances' posts, but when you copy the link to a post it gives you a 
link to your own instance. this link then either does a redirect (which 
is dangerous and mastodon is deprecating it), shows an interstitial (new 
versions of mastodon do this), or shows the cached content (most other 
instances do this).

doing a redirect is bad because it paves way for certain kinds of 
phishing attacks. but it preserves the original opengraph metadata, 
allowing for seamless link previews.

an interstitial is great because it reduces the chances of those 
phishing attacks. but it breaks the opengraph metadata, so you don't get 
link previews.

the third case we don't talk about because it's not really relevant to 
this post. (except minimally it is, more on that in a bit.)

so the Is-Autonomous header would ideally be set by link preview systems 
and not by anyone else (explicitly not by browsers). when a server sees 
Is-Autonomous, it could change its behaviour in any of the following ways:

- instead of showing an interstitial, it could do a redirect.
- instead of rendering an entire regular page template, it could render 
just the opengraph metadata.
- it could reject the request altogether.

the first 2 of these are great incentives to use the Is-Autonomous 
header: the first one makes link previews work, and the second one saves 
bandwidth both on the server and on the link preview system. we believe 
these benefits outweigh the drawback of the third for anyone interested 
in deploying this.

but enough with what we believe, what does the http wg think?