Allow configuring the origin of the service actor

config/config.exs

@@ -375,7 +375,8 @@
   follow_handshake_timeout: 500,
   note_replies_output_limit: 5,
   sign_object_fetches: true,
-  authorized_fetch_mode: false
+  authorized_fetch_mode: false,
+  fetch_actor_origin: nil
 
 config :pleroma, :streamer,
   workers: 3,

lib/pleroma/web/activity_pub/activity_pub_controller.ex

@@ -334,8 +334,16 @@ def relay(conn, _params) do
     |> represent_service_actor(conn)
   end
 
-  def internal_fetch(conn, _params) do
+  def internal_fetch(%Plug.Conn{host: host} = conn, _params) do
-    InternalFetchActor.get_actor()
+    with fetch_actor_origin when is_binary(fetch_actor_origin) <-
+           Pleroma.Config.get([:activitypub, :fetch_actor_origin]),
+         %URI{host: fetch_actor_host} <- URI.parse(fetch_actor_origin),
+         true <- host == fetch_actor_host do
+      fetch_actor_origin
+    else
+      _ -> Pleroma.Web.Endpoint.url()
+    end
+    |> InternalFetchActor.get_actor()
     |> represent_service_actor(conn)
   end
 

lib/pleroma/web/activity_pub/internal_fetch_actor.ex

@@ -11,10 +11,24 @@ def init do
     # Wait for everything to settle.
     Process.sleep(1000 * 5)
     get_actor()
+    get_actor(Pleroma.Web.Endpoint.url())
   end
 
-  def get_actor do
+  def get_actor(origin) do
-    "#{Pleroma.Web.Endpoint.url()}/internal/fetch"
+    %URI{host: host} = URI.parse(origin)
-    |> User.get_or_create_service_actor_by_ap_id("internal.fetch")
+
+    nickname =
+      cond do
+        host == Pleroma.Web.Endpoint.host() -> "internal.fetch"
+        true -> "internal.fetch@#{host}"
+      end
+
+    "#{origin}/internal/fetch"
+    |> User.get_or_create_service_actor_by_ap_id(nickname)
+  end
+
+  def get_actor() do
+    (Pleroma.Config.get([:activitypub, :fetch_actor_origin]) || Pleroma.Web.Endpoint.url())
+    |> get_actor()
   end
 end

test/pleroma/web/activity_pub/activity_pub_controller_test.exs

@@ -75,7 +75,7 @@ test "it returns the internal fetch user", %{conn: conn} do
         |> get(activity_pub_path(conn, :internal_fetch))
         |> json_response(200)
 
-      assert res["id"] =~ "/fetch"
+      assert res["id"] =~ "http://localhost:4001/internal/fetch"
     end
 
     test "on non-federating instance, it returns 404", %{conn: conn} do