Failling authentication

Question

I have a phoenix app where I want to secure all the routes except the login and user creation route. To achieve this, I use the Guardian and ComeOnIn packages. (I tried to follow this blog)
I managed to send a token to the client in the session route, and the creation of a user is working as well.
But, when I want to show all users (i.e. the index route of the user module) I get an authentication error (in my tests, I don't have the gui yet)
Here is what I have done: User controller:

defmodule WarehouseWeb.UserController do
  use WarehouseWeb, :controller

  alias Warehouse.Account
  alias Warehouse.Account.User

  action_fallback WarehouseWeb.FallbackController

  def index(conn, _params) do
    users = Account.list_users()
    render(conn, "index.json-api", data: users)
  end
# ... ...
end

Here is the router.ex

defmodule WarehouseWeb.Router do
  use WarehouseWeb, :router

  pipeline :api do
    plug :accepts, ["json", "json-api"]
  end

  pipeline :api_auth do
    plug WarehouseWeb.Guardian.AuthPipeline
  end

  scope "/api", WarehouseWeb do
    pipe_through :api
    post "/register", RegistrationController, :create
    post "/token", SessionController, :create, as: :login
  end

  scope "/api", WarehouseWeb do
    pipe_through :api_auth

    resources "/users", UserController, except: [:new, :edit]
  end
end

And here are the modules necessary for Guardian:

defmodule WarehouseWeb.Guardian.AuthPipeline do
  use Guardian.Plug.Pipeline, otp_app:       :warehouse,
                              module:        WarehouseWeb.Guardian,
                              error_handler: WarehouseWeb.Guardian.AuthErrorHandler

  plug Guardian.Plug.VerifyHeader
  plug Guardian.Plug.EnsureAuthenticated
end

defmodule Warehouse.Guardian do
  use Guardian, otp: :warehouse,
                secret_key: "some secret"

  def subject_for_token(resource, _claims) do
    {:ok, to_string(resource.id)}
  end
  def resource_from_claims(claims) do
    user = Warehouse.Account.get_user!(claims["sub"])
    {:ok,  user}
  end
end

The error handler:

defmodule WarehouseWeb.Guardian.AuthErrorHandler do
  import Plug.Conn

  def auth_error(conn, {type, reason}, opts) do
    IO.inspect "authentication is not working!!"
    body = Poison.encode!(%{message: to_string(type)})
    send_resp(conn, 401, body)
  end
end

And at last my test file:

defmodule WarehouseWeb.UserControllerTest do
  use WarehouseWeb.ConnCase

  alias Warehouse.Account
  alias Warehouse.Account.User

  @create_attrs %{email: "some email", firstname: "some firstname", lastname: "some lastname", password: "some password"}
  @update_attrs %{email: "some updated email", firstname: "some updated firstname", lastname: "some updated lastname", password: "some updated password"}
  @invalid_attrs %{email: nil, firstname: nil, lastname: nil, password: nil}

  def fixture(:user) do
    {:ok, user} = Account.create_user(@create_attrs)
    user
  end

  setup %{conn: conn} do
    # create user to be logged in
    {:ok, user} = Account.create_user(%{email: "[email protected]", real_password: "abc123", real_password_confirmation: "abc123"})

    # create token for session
    {:ok, jwt, _claims} = Account.authenticate(%{user: user, password: "abc123"})

    # add authorization header to the request
    conn = conn
    |> put_req_header("authorization", "Bearer: #{jwt}")
    |> put_req_header("accept", "application/json")

    {:ok, %{conn: conn, user: user}}
  end

  describe "index" do
    test "lists all users", %{conn: conn} do
      conn = get conn, user_path(conn, :index)
      assert json_response(conn, 200)["data"] == []
    end
  end
end

Everytime I run my test I always get the error Authentication already send, which comes from my error handler.
What am I missing to make my test pass?

EDIT:
Here is the output:

1) test index lists all users (WarehouseWeb.UserControllerTest) test/warehouse_web/controllers/user_controller_test.exs:32
** (Plug.Conn.AlreadySentError) the response was already sent
code: conn = get conn, user_path(conn, :index)
stacktrace:
(plug) lib/plug/conn.ex:508: Plug.Conn.resp/3
(plug) lib/plug/conn.ex:495: Plug.Conn.send_resp/3
(guardian) lib/guardian/plug/ensure_authenticated.ex:61: Guardian.Plug.EnsureAuthenticated.respond/1
(warehouse) lib/warehouse_web/auth/auth_pipeline.ex:1: WarehouseWeb.Guardian.AuthPipeline.plug_builder_call/2
(warehouse) lib/warehouse_web/router.ex:8: WarehouseWeb.Router.api_auth/2
(warehouse) lib/warehouse_web/router.ex:1: anonymous fn/1 in WarehouseWeb.Router.match_route/4
(phoenix) lib/phoenix/router.ex:273: Phoenix.Router.call/1
(warehouse) lib/warehouse_web/endpoint.ex:1: WarehouseWeb.Endpoint.plug_builder_call/2
(warehouse) lib/warehouse_web/endpoint.ex:1: WarehouseWeb.Endpoint.call/2
(phoenix) lib/phoenix/test/conn_test.ex:224: Phoenix.ConnTest.dispatch/5
test/warehouse_web/controllers/user_controller_test.exs:33: (test)

Answer 1

All your code seems pretty similar to mine, where it does work. The only difference is your test authentication... You have an extra semicolon there.

It should be

put_req_header("authorization", "Bearer #{token}")

Instead of

put_req_header("authorization", "Bearer: #{token}")

Hope that helps. Let me know if the issue persists