Scala web series Pt. 1 authorize a request based on its truthfulness

authorization_predicate_authorize_ops.scala

implicit AuthorizationOps(predicate: AuthorizationPredicate) { 
   def authorize[T](token: Token)(f: => Future[T]): Future[T] {
     if(predicate.evaluate(token)) {
        f()
      } else {
       Future.failed(AuthorizationException("..."))
      }
   }
}