Bootstrap Registration Toggle

Bootstrap Registration Toggle

Add the ability to enable/disable user registration via an environment variable in a Phoenix 1.8 app generated with phx.gen.auth.

Prerequisites

Verify before starting: 1. Phoenix 1.8 app with phx.gen.auth completed 2. A registration controller exists (e.g., UserRegistrationController) 3. A login page exists with a "Sign up" link

App Name Detection

Detect the app module name from mix.exs (e.g., MyApp) and the OTP app name (e.g., my_app). Replace all template references accordingly.

Phase 0: Discovery

CRITICAL: Before generating anything, audit the target app to understand what's already in place.

Discovery Checklist

1. Registration controller — Find the registration controller

• Grep("UserRegistrationController") or Grep("RegistrationController")
• Note the module name and file path

2. Existing toggle — Check if a registration toggle already exists

• Grep("registration_enabled") in config/ and lib/
• If found: report what exists and skip

3. Runtime config — Check for runtime.exs and existing boolean_env helper

• Read("config/runtime.exs")
• Note if boolean_env helper already exists (reuse it)

4. Login page — Find the login template with signup link

• Grep("register") in the session HTML templates
• Note the file path for conditional rendering

5. Router — Find registration routes

• Grep("register") in the router
• Note the scope and pipeline they're in

Discovery Report

Present findings and confirm before proceeding.

Phase 1: Configuration (only if no env var exists)

Ask the user:

1. ENV var name — What should the environment variable be called? Default: {APP_NAME_UPPER}_USER_REGISTRATION_ENABLED (e.g., MY_APP_USER_REGISTRATION_ENABLED)

2. Default behavior — Should registration be open or closed by default? Default: open in dev/test, closed in prod (config_env() != :prod)

3. Flash message — What message to show when registration is disabled? Default: "New account registration is temporarily unavailable."

4. Redirect path — Where to redirect when registration is disabled? Default: /users/log-in

Phase 2: Implementation

Step 1: Add boolean_env helper to runtime.exs (if not present)

If config/runtime.exs does not already have a boolean_env helper, add one near the top:

boolean_env = fn name, default ->
  case System.get_env(name) do
    nil -> default
    val -> String.downcase(val) in ~w(true 1 yes)
  end
end

Step 2: Add config entry to runtime.exs

Add the registration toggle config:

config :my_app,
       :user_registration_enabled,
       boolean_env.("MY_APP_USER_REGISTRATION_ENABLED", config_env() != :prod)

This means:

• dev/test: registration enabled by default (override with MY_APP_USER_REGISTRATION_ENABLED=false)
• prod: registration disabled by default (override with MY_APP_USER_REGISTRATION_ENABLED=true)

Step 3: Add controller plug guard

Add a private plug to the registration controller that checks the config:

plug(:ensure_registration_enabled)

# ... existing actions ...

@spec ensure_registration_enabled(Plug.Conn.t(), keyword()) :: Plug.Conn.t()
defp ensure_registration_enabled(conn, _opts) do
  if Application.get_env(:my_app, :user_registration_enabled, true) do
    conn
  else
    conn
    |> put_flash(:error, "New account registration is temporarily unavailable.")
    |> redirect(to: ~p"/users/log-in")
    |> halt()
  end
end

Important: The plug must be added BEFORE any action functions so it runs on every request.

Step 4: Conditionally hide the signup link on the login page

Find the login template (typically user_session_html/new.html.heex) and wrap the "Sign up" / "Register" link in a conditional:

<%= if Application.get_env(:my_app, :user_registration_enabled, true) do %>
  <p class="...">
    Don't have an account?
    <.link navigate={~p"/users/register"} class="...">Sign up</.link>
  </p>
<% end %>

This prevents confusion — users won't see a signup link that leads to a redirect.

Step 5: Add test coverage

Create or update tests for the registration controller:

describe "registration toggle" do
  test "allows registration when enabled", %{conn: conn} do
    Application.put_env(:my_app, :user_registration_enabled, true)
    on_exit(fn -> Application.delete_env(:my_app, :user_registration_enabled) end)

    conn = get(conn, ~p"/users/register")
    assert html_response(conn, 200) =~ "Register"
  end

  test "redirects when registration is disabled", %{conn: conn} do
    Application.put_env(:my_app, :user_registration_enabled, false)
    on_exit(fn -> Application.delete_env(:my_app, :user_registration_enabled) end)

    conn = get(conn, ~p"/users/register")
    assert redirected_to(conn) == "/users/log-in"
    assert Phoenix.Flash.get(conn.assigns.flash, :error) =~ "unavailable"
  end
end

Note: These tests must NOT be async: true since they modify application env.

Step 6: Verify

Run mix test to ensure nothing is broken.

Summary of Changes

ENV Variable Reference

Bootstrap Registration Toggle

Add ENV-based registration toggle to a Phoenix 1.8 app.

Install

Install this skill globally:

npx skills add agoodway/GoodSkills --skill bootstrap-registration-toggle -g

Install into the current project:

npx skills add agoodway/GoodSkills --skill bootstrap-registration-toggle

Usage

/bootstrap-registration-toggle