public function signOutAllSessions(UserInterface $user)
    {
        $db = $this->getDatabase();

        // invalidate any active sessions
        $db->update('ActiveSessions')
           ->values(['valid' => 0])
           ->where('user_id', $user->id())
           ->execute();

        // invalidate any remember me sessions
        $db->delete('PersistentSessions')
           ->where('user_id', $user->id())
           ->execute();

        return true;
    }