activitypub: publisher: add (request-target) to http signature when POSTing

CHANGELOG.md

@@ -37,6 +37,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 - Rich Media: The crawled URL is now spliced into the rich media data.
 - ActivityPub S2S: sharedInbox usage has been mostly aligned with the rules in the AP specification.
 - ActivityPub S2S: remote user deletions now work the same as local user deletions.
+- ActivityPub S2S: POST requests are now signed with `(request-target)` pseudo-header.
 - Not being able to access the Mastodon FE login page on private instances
 - Invalid SemVer version generation, when the current branch does not have commits ahead of tag/checked out on a tag
 - Pleroma.Upload base_url was not automatically whitelisted by MediaProxy. Now your custom CDN or file hosting will be accessed directly as expected.

lib/pleroma/web/activity_pub/publisher.ex

@@ -46,7 +46,9 @@ def is_representable?(%Activity{} = activity) do
   """
   def publish_one(%{inbox: inbox, json: json, actor: %User{} = actor, id: id} = params) do
     Logger.info("Federating #{id} to #{inbox}")
-    host = URI.parse(inbox).host
+    uri = URI.parse(inbox)
+    host = uri.host
+    path = uri.path
 
     digest = "SHA-256=" <> (:crypto.hash(:sha256, json) |> Base.encode64())
 
@@ -56,6 +58,7 @@ def publish_one(%{inbox: inbox, json: json, actor: %User{} = actor, id: id} = pa
 
     signature =
       Pleroma.Signature.sign(actor, %{
+        "(request-target)": "post #{path}",
         host: host,
         "content-length": byte_size(json),
         digest: digest,