When a user signs up, then I want to run some checks before I let him into the app.
E.g. check if he is already affiliated with an existing Company.
Do I write a plug or do I do something else? 
I’m using auth.gen for authentication.
Best,
Martin
Are these things that would block signing up or not? Based on your example, I’ll assume they’re not.
In one of our apps, we perform similar tasks and really like using Oban to handle these background jobs. We enqueue the jobs in Accounts.create_user/1, which manages everything within an %Ecto.Multi{}. For your case it would be something like this:
defmodule MyApp.Users.CheckUsersExistingCompaniesWorker do
use Oban.Worker,
queue: :default,
priority: 3,
max_attempts: 3,
tags: ["users"],
unique: [period: 30]
@impl Oban.Worker
def perform(%Oban.Job{args: %{"user_id" => user_id}}) do
# do the check, maybe update db
# :ok | {:ok, value} | {:cancel, reason} | {:error, error} | {:snooze, seconds}
end
end
defmodule MyApp.Users do
def enqueue_existing_companies_job(user_id) do
%{user_id: user_id}
|> __MODULE__.CheckUsersExistingCompaniesWorker.new()
|> Oban.insert()
end
end
You could choose your preferred method of spawning processes, but if you want an easy and solid solution, then I’d recommend going with a robust library like Oban or a similar one.
But if you’re talking about things that would block signing up or in, then you’d want to do this in a Plug or an on_mount handler for LiveView.
A plug for this use case would be something along the lines of this:
defmodule MyAppWeb.Plugs.CheckUserCompany do
import Plug.Conn
def init(_opts), do: %{}
def call(conn, _opts) do
case MyApp.SomeContext.affiliated_with_existing_company?(conn.assigns.current_user) do
true ->
conn
|> put_flash(:error, "Not allowed")
|> redirect(to: "/")
false ->
conn
end
end
end
And an on_mount handler like this:
defmodule MyAppWeb.Live.OnMountHandlers do
def on_mount(:affiliated_with_existing_company, _params, _session, socket) do
case MyApp.SomeContext.affiliated_with_existing_company?(socket.assigns.current_user) do
true -> {:halt, redirect(socket, to: "/")}
false -> {:cont, socket}
end
end
end
Or whatever the logic is behind that check.
