Play Framework: Dependency Inject Action Builder - scala

Question

since Play Framework 2.4 there is the possibility to use dependency injection (with Guice).
Before I used objects (for example AuthenticationService) in my ActionBuilders:
object AuthenticatedAction extends ActionBuilder[AuthenticatedRequest] {
override def invokeBlock[A](request: Request[A], block: (AuthenticatedRequest[A]) => Future[Result]): Future[Result] = {
...
AuthenticationService.authenticate (...)
...
}
}
Now AuthenticationService is not an object anymore, but a class. How can I still use the AuthenticationService in my ActionBuilder?

Answer 1

Define your action builders inside a trait with the authentication service as an abstract field. Then mix them into your controllers, into which you inject the service. For example:
trait MyActionBuilders {
// the abstract dependency
def authService: AuthenticationService
def AuthenticatedAction = new ActionBuilder[AuthenticatedRequest] {
override def invokeBlock[A](request: Request[A], block(AuthenticatedRequest[A]) => Future[Result]): Future[Result] = {
authService.authenticate(...)
...
}
}
}
and the controller:
#Singleton
class MyController #Inject()(authService: AuthenticationService) extends Controller with MyActionBuilders {
def myAction(...) = AuthenticatedAction { implicit request =>
Ok("authenticated!")
}
}

Answer 2

I didn't like the way one was required to inherit in the above example. But apparently it's possible to simply wrap a object inside class:
class Authentication #Inject()(authService: AuthenticationService) {
object AuthenticatedAction extends ActionBuilder[Request] {
def invokeBlock[A](request: Request[A], block: (Request[A]) => Future[Result]) = {
// Do your thing wit the authService...
block(request)
}
}
}
class YourController #Inject() (val auth: Authentication) extends Controller (
def loggedInUser = auth.AuthenticatedAction(parse.json) { implicit request =>
// ...
}
}

Answer 3

I like accepted answer but for some reason the compiler would not recognize the authService reference. I got around this pretty easily by just sending the service in the method signature, a la...
class Authentication #Inject()(authenticationService: AuthenticationService) extends Controller with ActionBuilders {
def testAuth = AuthenticatedAction(authenticationService).async { implicit request =>
Future.successful(Ok("Authenticated!"))
}
}