I’m working on an app that uses Pow to handle user authentication. I was able to get it working by following the documentation, but I ran into an issue that I don’t see a clear solution for.

The application is for a subscription service where new users are given a free trial after signing up. I use Pow to create the user, which works fine. Now, I’m trying to associate the newly created user with a subscription using the controller callback feature from the Phoenix controllers section of the README. Here’s my implementation so far:

defmodule AddSubscription.Phoenix.ControllerCallbacks do
  use Pow.Extension.Phoenix.ControllerCallbacks.Base

  require Logger

  @impl true
  def before_respond(Pow.Phoenix.RegistrationController, :create, {:ok, user, conn}, _config) do
    Logger.debug("user registration before_respond: #{inspect(user)}")
    with {:ok, user} <- Trumpet.insert_subscription(%{user_id: user.id}) do
      {:ok, user, conn}
    end
  end
end

I’ve also written a controller test to exercise the behavior works as intended:

defmodule Pow.Phoenix.RegistrationControllerTest do
  use TrumpetWeb.ConnCase

  describe "POST /registration" do
    test "creates a user with a subscription", %{conn: conn} do
      email = "wembley.gl@gmail.com"
      post(
        conn,
        "/registration",
        %{
          user: %{
            email: email,
            password: "test1234567890",
            confirm_password: "test1234567890",
          }
        }
      )
      user = Trumpet.get_user_by_email_with_subscription(email)
      assert user.subscription
      assert Trumpet.Subscription.trial?(user.subscription)
    end
  end
end

The user creation works as expected, but the controller callback isn’t firing, so the assertion for user.subscription fails. I’ve taken a look at the Extensions section for Pow, from here, and looked at the implementation for other extensions, like PowPasswordReset, and it looks like an extension should be implemented as a library application, is that right? Also, how do I configure Pow to register an extension once it’s created? I apologize if this is in the documentation and I’m missing it.