@trwnh Actually, Fedify already supports this quite well. The actor dispatcher gives you full control over the actor's id—you can set it to any URL, including one on a custom domain. And since Fedify 1.4.0, there's a mapAlias() method that lets you handle WebFinger lookups for those custom URLs too. So running Fedify behind a reverse proxy that routes multiple hostnames, and assigning per-actor custom domain identifiers, should be achievable without any changes to Fedify itself.

@hongminhee so are object ids handled outside of fedify? the application written around fedify would have to keep track of which ids are already used/assigned?