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

lib/pleroma/web/activity_pub/publisher.ex

@@ -46,7 +46,9 @@ defmodule Pleroma.Web.ActivityPub.Publisher 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 @@ defmodule Pleroma.Web.ActivityPub.Publisher do
 
     signature =
       Pleroma.Signature.sign(actor, %{
+        "(request-target)": "post #{path}",
         host: host,
         "content-length": byte_size(json),
         digest: digest,