I think the absolutely least understood feature of ActivityPub is `proxyUrl`.

This is the feature that lets you ask your ActivityPub server to fetch AP objects from other servers on your behalf, using your identity.

This is what lets you get private or followers-only content from other servers.

Every. Single. AP. Server. should. implement. `proxyUrl`.

@evan It's great, but it's missing the spec bits about what exactly is "your identity" and how you establish that to "other servers". (And no, I don't think the current HTTP Signatures mess is a suitable solution to this question. I'd like to see other forms of cross-domain authentication and/or authorization be better supported, preferably something based on bearer or capability tokens. At the very least something using the Authorization / WWW-Authenticate header mechanisms that already exist!)