guardian_shiz.ex

defmodule Foo.SessionController do
  use Foo.Web, :controller
  
  def create(conn, %{"session" => session_params}) do
    case Foo.Session.authenticate(session_params) do
      {:ok, user} ->
        {:ok, jwt, _full_claims} = Guardian.encode_and_sign(user, :token)
        
        conn
        |> put_status(:created)
        |> render("show.json", jwt: jwt, user: user)
      
      :error ->
        conn
        |> put_status(:unprocessable_entity)
        |> render("error.json")
    end
  end
  
  def unauthenticated(conn, _params) do
    conn
    |> put_status(:forbidden)
    |> render(Foo.SessionView, "forbidden.json", error: "Not Authenticated")
  end
end

defmodule Foo.SomeOtherController do
  use Foo.Web, :controller
  
  plug Guardian.Plug.EnsureAuthenticated, handler: Foo.SessionController
end