class SignInActivity : AppCompatActivity() {
    ...
fun authorizeUser(username: String, password: String) {
  doAsync {
    val authorized = signInBL.checkUserCredentials(
          AuthCredentials(username = username, password = password))
    activityUiThread {
       if (authorized) {
          toast("Signed!!!")
       } else {
          view.showAccessDeniedAlertDialog()
       }
    }
   }
}