aprs.me/lib/aprsme_web/user_auth.ex

defmodule AprsmeWeb.UserAuth do
  @moduledoc false
  use AprsmeWeb, :verified_routes

  import Phoenix.Controller
  import Plug.Conn

  alias Aprsme.Accounts

  # Make the remember me cookie valid for 60 days.
  # If you want bump or reduce this value, also change
  # the token expiry itself in UserToken.
  alias Phoenix.LiveView.Socket

  @max_age 60 * 60 * 24 * 60
  @remember_me_cookie "_aprs_web_user_remember_me"
  @remember_me_options [sign: true, max_age: @max_age, same_site: "Lax"]

  @doc """
  Logs the user in.

  It renews the session ID and clears the whole session
  to avoid fixation attacks. See the renew_session
  function to customize this behaviour.

  It also sets a `:live_socket_id` key in the session,
  so LiveView sessions are identified and automatically
  disconnected on log out. The line can be safely removed
  if you are not using LiveView.
  """
  @spec log_in_user(Plug.Conn.t(), Aprsme.Accounts.User.t(), map()) :: Plug.Conn.t()
  def log_in_user(conn, user, params \\ %{}) do
    token = Accounts.generate_user_session_token(user)
    user_return_to = get_session(conn, :user_return_to)

    conn
    |> renew_session()
    |> put_token_in_session(token)
    |> maybe_write_remember_me_cookie(token, params)
    |> redirect(to: user_return_to || signed_in_path(conn))
  end

  @spec maybe_write_remember_me_cookie(Plug.Conn.t(), String.t(), map()) :: Plug.Conn.t()
  defp maybe_write_remember_me_cookie(conn, token, %{"remember_me" => "true"}) do
    put_resp_cookie(conn, @remember_me_cookie, token, @remember_me_options)
  end

  defp maybe_write_remember_me_cookie(conn, _token, _params), do: conn

  # This function renews the session ID and erases the whole
  # session to avoid fixation attacks. If there is any data
  # in the session you may want to preserve after log in/log out,
  # you must explicitly fetch the session data before clearing
  # and then immediately set it after clearing, for example:
  #
  #     defp renew_session(conn) do
  #       preferred_locale = get_session(conn, :preferred_locale)
  #
  #       conn
  #       |> configure_session(renew: true)
  #       |> clear_session()
  #       |> put_session(:preferred_locale, preferred_locale)
  #     end
  #
  @spec renew_session(Plug.Conn.t()) :: Plug.Conn.t()
  defp renew_session(conn) do
    conn
    |> configure_session(renew: true)
    |> clear_session()
  end

  @doc """
  Logs the user out.

  It clears all session data for safety. See renew_session.
  """
  @spec log_out_user(Plug.Conn.t()) :: Plug.Conn.t()
  def log_out_user(conn) do
    user_token = get_session(conn, :user_token)
    user_token && Accounts.delete_user_session_token(user_token)

    if live_socket_id = get_session(conn, :live_socket_id) do
      AprsmeWeb.Endpoint.broadcast(live_socket_id, "disconnect", %{})
    end

    conn
    |> renew_session()
    |> delete_resp_cookie(@remember_me_cookie)
    |> redirect(to: "/")
  end

  @doc """
  Authenticates the user by looking into the session
  and remember me token.
  """
  @spec fetch_current_user(Plug.Conn.t(), any()) :: Plug.Conn.t()
  def fetch_current_user(conn, _opts) do
    {user_token, conn} = ensure_user_token(conn)
    user = user_token && Accounts.get_user_by_session_token(user_token)
    assign(conn, :current_user, user)
  end

  @spec ensure_user_token(Plug.Conn.t()) :: {String.t() | nil, Plug.Conn.t()}
  defp ensure_user_token(conn) do
    case get_session(conn, :user_token) do
      nil -> ensure_user_token_from_cookie(conn)
      token -> {token, conn}
    end
  end

  @spec ensure_user_token_from_cookie(Plug.Conn.t()) :: {String.t() | nil, Plug.Conn.t()}
  defp ensure_user_token_from_cookie(conn) do
    conn = fetch_cookies(conn, signed: [@remember_me_cookie])

    case conn.cookies[@remember_me_cookie] do
      nil -> {nil, conn}
      token -> {token, put_token_in_session(conn, token)}
    end
  end

  @doc """
  Handles mounting and authenticating the current_user in LiveViews.

  ## `on_mount` arguments

    * `:mount_current_user` - Assigns current_user
      to socket assigns based on user_token, or nil if
      there's no user_token or no matching user.

    * `:ensure_authenticated` - Authenticates the user from the session,
      and assigns the current_user to socket assigns based
      on user_token.
      Redirects to login page if there's no logged user.

    * `:redirect_if_user_is_authenticated` - Authenticates the user from the session.
      Redirects to signed_in_path if there's a logged user.

  ## Examples

  Use the `on_mount` lifecycle macro in LiveViews to mount or authenticate
  the current_user:

      defmodule AprsmeWeb.PageLive do
        use AprsmeWeb, :live_view

        on_mount {AprsmeWeb.UserAuth, :mount_current_user}
        ...
      end

  Or use the `live_session` of your router to invoke the on_mount callback:

      live_session :authenticated, on_mount: [{AprsmeWeb.UserAuth, :ensure_authenticated}] do
        live "/profile", ProfileLive, :index
      end
  """
  @spec on_mount(atom(), map(), map(), Socket.t()) :: {:cont | :halt, Socket.t()}
  def on_mount(:mount_current_user, _params, session, socket) do
    {:cont, mount_current_user(session, socket)}
  end

  def on_mount(:ensure_authenticated, _params, session, socket) do
    socket = mount_current_user(session, socket)

    case socket.assigns.current_user do
      nil ->
        socket =
          socket
          |> Phoenix.LiveView.put_flash(:error, "You must log in to access this page.")
          |> Phoenix.LiveView.redirect(to: ~p"/users/log_in")

        {:halt, socket}

      _user ->
        {:cont, socket}
    end
  end

  def on_mount(:redirect_if_user_is_authenticated, _params, session, socket) do
    socket = mount_current_user(session, socket)

    case socket.assigns.current_user do
      nil -> {:cont, socket}
      _user -> {:halt, Phoenix.LiveView.redirect(socket, to: signed_in_path(socket))}
    end
  end

  @spec mount_current_user(map(), Socket.t()) :: Socket.t()
  defp mount_current_user(session, socket) do
    case session do
      %{"user_token" => user_token} ->
        Phoenix.Component.assign_new(socket, :current_user, fn ->
          Accounts.get_user_by_session_token(user_token)
        end)

      %{} ->
        Phoenix.Component.assign_new(socket, :current_user, fn -> nil end)
    end
  end

  @doc """
  Used for routes that require the user to not be authenticated.
  """
  @spec redirect_if_user_is_authenticated(Plug.Conn.t(), any()) :: Plug.Conn.t()
  def redirect_if_user_is_authenticated(conn, _opts) do
    case conn.assigns[:current_user] do
      nil ->
        conn

      _user ->
        conn
        |> redirect(to: signed_in_path(conn))
        |> halt()
    end
  end

  @doc """
  Used for routes that require the user to be authenticated.

  If you want to enforce the user email is confirmed before
  they use the application at all, here would be a good place.
  """
  @spec require_authenticated_user(Plug.Conn.t(), any()) :: Plug.Conn.t()
  def require_authenticated_user(conn, _opts) do
    case conn.assigns[:current_user] do
      nil ->
        conn
        |> put_flash(:error, "You must log in to access this page.")
        |> maybe_store_return_to()
        |> redirect(to: ~p"/users/log_in")
        |> halt()

      _user ->
        conn
    end
  end

  @spec put_token_in_session(Plug.Conn.t(), String.t()) :: Plug.Conn.t()
  defp put_token_in_session(conn, token) do
    conn
    |> put_session(:user_token, token)
    |> put_session(:live_socket_id, "users_sessions:#{Base.url_encode64(token)}")
  end

  @spec maybe_store_return_to(Plug.Conn.t()) :: Plug.Conn.t()
  defp maybe_store_return_to(%{method: "GET"} = conn) do
    put_session(conn, :user_return_to, current_path(conn))
  end

  defp maybe_store_return_to(conn), do: conn

  @spec signed_in_path(Plug.Conn.t() | Socket.t()) :: String.t()
  defp signed_in_path(_conn), do: ~p"/"
end