Gate registration to ALLOWED_REGISTRATION_EMAIL

app/lib/firehose_web/controllers/user_registration_controller.ex

@@ -10,23 +10,35 @@ defmodule FirehoseWeb.UserRegistrationController do
   end
 
   def create(conn, %{"user" => user_params}) do
-    case Accounts.register_user(user_params) do
-      {:ok, user} ->
-        {:ok, _} =
-          Accounts.deliver_login_instructions(
-            user,
-            &url(~p"/users/log-in/#{&1}")
+    allowed_email = Application.get_env(:firehose, :allowed_registration_email)
+
+    if allowed_email == nil or user_params["email"] != allowed_email do
+      changeset =
+        %User{}
+        |> Accounts.change_user_email(user_params)
+        |> Ecto.Changeset.add_error(:email, "registration is invite only.")
+        |> Map.put(:action, :validate)
+
+      render(conn, :new, changeset: changeset)
+    else
+      case Accounts.register_user(user_params) do
+        {:ok, user} ->
+          {:ok, _} =
+            Accounts.deliver_login_instructions(
+              user,
+              &url(~p"/users/log-in/#{&1}")
+            )
+
+          conn
+          |> put_flash(
+            :info,
+            "An email was sent to #{user.email}, please access it to confirm your account."
           )
+          |> redirect(to: ~p"/users/log-in")
 
-        conn
-        |> put_flash(
-          :info,
-          "An email was sent to #{user.email}, please access it to confirm your account."
-        )
-        |> redirect(to: ~p"/users/log-in")
-
-      {:error, %Ecto.Changeset{} = changeset} ->
-        render(conn, :new, changeset: changeset)
+        {:error, %Ecto.Changeset{} = changeset} ->
+          render(conn, :new, changeset: changeset)
+      end
     end
   end
 end