Add Cron worker to clean up orphaned apps hourly

lib/pleroma/web/o_auth/app.ex

@@ -165,4 +165,10 @@ defmodule Pleroma.Web.OAuth.App do
   end
 
   def maybe_update_owner(_), do: :ok
+
+  @spec remove_orphans() :: :ok
+  def remove_orphans() do
+    from(a in __MODULE__, where: is_nil(a.user_id))
+    |> Repo.delete_all()
+  end
 end

lib/pleroma/workers/cron/app_cleanup_worker.ex

@@ -0,0 +1,21 @@
+# Pleroma: A lightweight social networking server
+# Copyright © 2017-2022 Pleroma Authors <https://pleroma.social/>
+# SPDX-License-Identifier: AGPL-3.0-only
+
+defmodule Pleroma.Workers.Cron.AppCleanupWorker do
+  @moduledoc """
+  Cleans up registered apps that were never associated with a user.
+  """
+
+  use Oban.Worker, queue: "background"
+
+  alias Pleroma.Web.OAuth.App
+
+  @impl true
+  def perform(_job) do
+    App.remove_orphans()
+  end
+
+  @impl true
+  def timeout(_job), do: :timer.seconds(30)
+end