Return webfinger for ap_ids.

lib/pleroma/web/web_finger/web_finger.ex

@@ -18,11 +18,15 @@ defmodule Pleroma.Web.WebFinger do
   def webfinger(resource) do
     host = Pleroma.Web.host
     regex = ~r/(acct:)?(?<username>\w+)@#{host}/
-    case Regex.named_captures(regex, resource) do
-      %{"username" => username} ->
-        user = User.get_by_nickname(username)
+    with %{"username" => username} <- Regex.named_captures(regex, resource) do
+      user = User.get_by_nickname(username)
+      {:ok, represent_user(user)}
+    else _e ->
+      with user when not is_nil(user) <- User.get_cached_by_ap_id(resource) do
         {:ok, represent_user(user)}
-      _ -> nil
+      else _e ->
+        {:error, "Couldn't find user"}
+      end
     end
   end