Authentication

User authentication can be handled in many ways! In this example, we'll define custom pages that:

1. Are only visible when a user is logged in
2. Redirect to a sign in page otherwise.
3. Still benefit from elm-spa's route generation!

Let's assume we have a user : Maybe User field in the Shared.Model, and have a sign-in page at SignIn.elm!

Creating Custom Pages

Because Spa/Page.elm is in your project, you can use it to define your own custom page functions.

As long as those functions return the same Page type, they are valid! The only downside is that they won't be available for elm-spa add command.

If your app involves user authentication, you could make a protectedSandbox page type that always gets a User, and redirects if one is missing:

-- within Spa/Page.elm

protectedSandbox :
  { init : User -> Url params -> model
  , update : msg -> model -> model
  , view : model -> Document msg
  }
  -> Page params (Maybe model) msg
protectedSandbox options =
  { init =
      \shared url ->
        case shared.user of
          Just user ->
            options.init user url |> Tuple.mapFirst Just

          Nothing ->
            ( Nothing
            , Nav.pushUrl url.key (Route.toString Route.SignIn)
            )
  , update = -- ... conditionally call options.update
  , view = -- ... conditionally call options.view
  , subscriptions = \_ -> Sub.none
  , save = \_ shared -> shared
  , load = \_ model -> ( model, Cmd.none )
  }

As long as you return a Page type, your page will work with the rest of elm-spa's automated routing!

Usage

-- (within an actual page)

type alias Model = Maybe SafeModel

page : Page Params Model Msg
page =
  Page.protectedSandbox
    { init = init
    , update = update
    , view = view
    }

init : User -> Url Params -> SafeModel
update : Msg -> SafeModel -> SafeModel
view : SafeModel -> Document Msg

One caveat is that the Model type exposed by your page is used by the generated code, so your actual model will need a different name (like SafeModel).

But now you know that these functions will only be called if the User is really logged in!

---

That's it! Swing by the #elm-spa-users channel and say hello!