Listen to auth events

final subscription = Amplify.Hub.listen(HubChannel.Auth, (AuthHubEvent event) {
  switch (event.type) {
    case AuthHubEventType.signedIn:
      safePrint('User is signed in.');
      break;
    case AuthHubEventType.signedOut:
      safePrint('User is signed out.');
      break;
    case AuthHubEventType.sessionExpired:
      safePrint('The session has expired.');
      break;
    case AuthHubEventType.userDeleted:
      safePrint('The user has been deleted.');
      break;
  }
});