How to add plug in router in phoenix elixir

Question

I create authentication for users resource and it works fine but now i want to use the authenticate function from user_controller.ex to project_controller.ex.

If i copy authenticate private function from user_controller to project_controller than authentication works on projects resource but i don't want to duplicate this authenticate function in every controller. i need to know what is the best approach to dry this code. i think the router is the good place to add the authenticate plug but i need to know where should i add the code.

router.ex

defmodule Auth.Router do
  use Auth.Web, :router

  pipeline :browser do
    plug :accepts, ["html"]
    plug :fetch_session
    plug :fetch_flash
    plug :protect_from_forgery
    plug :put_secure_browser_headers
    plug Auth.Auth, repo: Auth.Repo
  end

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

  scope "/", Auth do
    pipe_through :browser # Use the default browser stack

    get "/", PageController, :index
    resources "/users", UserController
    resources "/sessions", SessionController, only: [:new, :create, :delete]
    resources "/projects", ProjectController
  end
end

user_controller.ex

defmodule Auth.UserController do
  use Auth.Web, :controller

  plug :authenticate when action in [:index, :show]

  alias Auth.User

  plug :scrub_params, "user" when action in [:create, :update]

  def index(conn, _params) do
    users = Repo.all(User)
    render(conn, "index.html", users: users)
  end

  def new(conn, _params) do
    changeset = User.changeset(%User{})
    render(conn, "new.html", changeset: changeset)
  end

  def create(conn, %{"user" => user_params}) do
    changeset = User.registration_changeset(%User{}, user_params)

    case Repo.insert(changeset) do
      {:ok, user} ->
        conn
        |> Auth.Auth.login(user)
        |> put_flash(:info, "#{user.username} created successfully.")
        |> redirect(to: user_path(conn, :index))
      {:error, changeset} ->
        render(conn, "new.html", changeset: changeset)
    end
  end

  def show(conn, %{"id" => id}) do
    user = Repo.get!(User, id)
    render(conn, "show.html", user: user)
  end

  def edit(conn, %{"id" => id}) do
    user = Repo.get!(User, id)
    changeset = User.changeset(user)
    render(conn, "edit.html", user: user, changeset: changeset)
  end

  def update(conn, %{"id" => id, "user" => user_params}) do
    user = Repo.get!(User, id)
    changeset = User.changeset(user, user_params)

    case Repo.update(changeset) do
      {:ok, user} ->
        conn
        |> put_flash(:info, "User updated successfully.")
        |> redirect(to: user_path(conn, :show, user))
      {:error, changeset} ->
        render(conn, "edit.html", user: user, changeset: changeset)
    end
  end

  def delete(conn, %{"id" => id}) do
    user = Repo.get!(User, id)
    Repo.delete!(user)
    conn
    |> put_flash(:info, "User deleted successfully.")
    |> redirect(to: user_path(conn, :index))
  end

  defp authenticate(conn, _opts) do
    if conn.assigns.current_user do
      conn
    else
      conn
      |> put_flash(:error, "You must be login to access that page.")
      |> redirect(to: page_path(conn, :index))
      |> halt()
    end
  end
end

models/user.ex

defmodule Auth.User do
  use Auth.Web, :model

  schema "users" do
    field :username, :string
    field :password_hash, :string
    field :password, :string, virtual: true

    timestamps
  end

  def changeset(model, params \\ :empty) do
    model
    |> cast(params, ~w(username), [])
    |> validate_length(:username, min: 3, max: 20)

  end

  def registration_changeset(model, params) do
    model
    |> changeset(params)
    |> cast(params, ~w(password), [])
    |> validate_length(:password, min: 6, max: 100)
    |> put_pass_hash()
  end

  defp put_pass_hash(changeset) do
    case changeset do
      %Ecto.Changeset{valid?: true, changes: %{password: pass}} ->
        put_change(changeset, :password_hash, Comeonin.Bcrypt.hashpwsalt(pass))
      _ -> 
        changeset  
    end
  end
end

controllers/auth.ex

defmodule Auth.Auth do
  import Plug.Conn
  import Comeonin.Bcrypt, only: [checkpw: 2]

  def init(opts) do
    Keyword.fetch!(opts, :repo)
  end

  def call(conn, repo) do
    user_id = get_session(conn, :user_id)
    user = user_id && repo.get(Auth.User, user_id)
    assign(conn, :current_user, user)
  end

  def login(conn, user) do
    conn
    |> assign(:current_user, user)
    |> put_session(:user_id, user.id)
    |> configure_session(renew: true)
  end

  def login_by_username_and_pass(conn, username, given_pass, opts) do
    repo = Keyword.fetch!(opts, :repo)
    user = repo.get_by(Auth.User, username: username)
    cond do
      user && checkpw(given_pass, user.password_hash) ->
        {:ok, login(conn, user)}
      user ->
        {:error, :unauthorized, conn}
      true -> 
        {:error, :not_found, conn}
    end
  end

  def logout(conn) do
    # configure_session(conn, drop: true)
    delete_session(conn, :user_id)
  end

end

controllers/project_controller.ex

defmodule Auth.ProjectController do
  use Auth.Web, :controller

  plug :authenticate when action in [:index, :new, :show]

  alias Auth.Project

  plug :scrub_params, "project" when action in [:create, :update]

  def index(conn, _params) do
    projects = Repo.all(Project)
    render(conn, "index.html", projects: projects)
  end

  def new(conn, _params) do
    changeset = Project.changeset(%Project{})
    render(conn, "new.html", changeset: changeset)
  end

  def create(conn, %{"project" => project_params}) do
    changeset = Project.changeset(%Project{}, project_params)

    case Repo.insert(changeset) do
      {:ok, _project} ->
        conn
        |> put_flash(:info, "Project created successfully.")
        |> redirect(to: project_path(conn, :index))
      {:error, changeset} ->
        render(conn, "new.html", changeset: changeset)
    end
  end

  def show(conn, %{"id" => id}) do
    project = Repo.get!(Project, id)
    render(conn, "show.html", project: project)
  end

  def edit(conn, %{"id" => id}) do
    project = Repo.get!(Project, id)
    changeset = Project.changeset(project)
    render(conn, "edit.html", project: project, changeset: changeset)
  end

  def update(conn, %{"id" => id, "project" => project_params}) do
    project = Repo.get!(Project, id)
    changeset = Project.changeset(project, project_params)

    case Repo.update(changeset) do
      {:ok, project} ->
        conn
        |> put_flash(:info, "Project updated successfully.")
        |> redirect(to: project_path(conn, :show, project))
      {:error, changeset} ->
        render(conn, "edit.html", project: project, changeset: changeset)
    end
  end

  def delete(conn, %{"id" => id}) do
    project = Repo.get!(Project, id)

    # Here we use delete! (with a bang) because we expect
    # it to always work (and if it does not, it will raise).
    Repo.delete!(project)

    conn
    |> put_flash(:info, "Project deleted successfully.")
    |> redirect(to: project_path(conn, :index))
  end


  # defp authenticate(conn, _opts) do
  #   if conn.assigns.current_user do
  #     conn
  #   else
  #     conn
  #     |> put_flash(:error, "You must be login to access that page.")
  #     |> redirect(to: page_path(conn, :index))
  #     |> halt()
  #   end
  # end
end

Answer 1

This is a fairly common pattern. First you need your Authenticate plug:

defmodule Auth.Plug.Authenticate do
  @behaviour Plug
  import Plug.Conn
  import Phoenix.Controller, only: [put_flash: 3, redirect: 2]

  def init(opts), do: opts

  def call(conn, _opts) do
    if conn.assigns.current_user do
      conn
    else
      conn
      |> put_flash(:error, "You must be login to access that page.")
      |> redirect(to: Auth.Router.Helpers.page_path(conn, :index))
      |> halt()
    end
  end
end

Then in your router you can do:

defmodule Auth.Router do
  use Auth.Web, :router

  pipeline :browser do
    plug :accepts, ["html"]
    plug :fetch_session
    plug :fetch_flash
    plug :protect_from_forgery
    plug :put_secure_browser_headers
    plug Auth.Auth, repo: Auth.Repo
  end

  pipeline :authenticated do
    plug Auth.Plug.Authenticate, repo: Auth.Repo
  end

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

  scope "/", Auth do
    pipe_through :browser # Use the default browser stack

    get "/", PageController, :index
    resources "/sessions", SessionController, only: [:new, :create]
  end

  scope "/", Auth do
    pipe_through [:browser, :authenticated]

    resources "/users", UserController
    resources "/sessions", SessionController, only: [:delete]
    resources "/projects", ProjectController
  end
end