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@evan This is my mistake, thanks for pointing out. It should be changed to "...where embedded objects are owned by another local actor".

I think Create.object.attributedTo == Create.actor is a different thing, because it is related to authorization, whereas the requirement we're discussing here is related to authentication.

In general, yes, none of this was built into ActivityPub. But over the years implementers figured out authentication and authorization on their own, and now this is how federation works. People expect that same-origin embeddings can be cached as is, without re-fetching.

@general

@silverpill
>this measure is ineffective and can easily be circumvented by changing the keyId parameter of a signature.

I never thought about it like that, but that too is a way to circumvent it. Although you would still need some way to publish that key and a valid Actor for verification, a server. If a remote server implementing restrictions on fetching based on signatures only disallows the instance Actor, then that is a way to bypass that restriction. Although I think there currently is no implementation that does that. Mastodon instead blocks everything on the domain including all subdomains and GTS probably does the same. No idea how the Misskey forks and Iceshrimp.NET do it though. Of course using different domains works as well.

>Servers MUST NOT allow clients to publish activities where embedded objects are owned by another actor.

Unrelated to the this FEP, but this came up when fixing the recent Pleroma security issues. There is no agreed upon way of federating moderation decisions to remote instances. It is logical when validating remote Update Activities to only allow Activities that update Objects owned by the same Actor, however that is never guaranteed when for example an admin on a remote instance forces a post to be NSFW. Similarly Delete Activities can have the Actor be the moderator, but Object actually owned by user.