More logging.

lib/pleroma/plugs/http_signature.ex

 defmodule Pleroma.Web.Plugs.HTTPSignaturePlug do
   alias Pleroma.Web.HTTPSignatures
   import Plug.Conn
+  require Logger
 
   def init(options) do
     options
@@ -11,6 +12,8 @@ def call(%{assigns: %{valid_signature: true}} = conn, opts) do
   end
 
   def call(conn, opts) do
+    user = conn.params["actor"]
+    Logger.debug("Checking sig for #{user}")
     if get_req_header(conn, "signature") do
       conn = conn
       |> put_req_header("(request-target)", String.downcase("#{conn.method} #{conn.request_path}"))