protected function initializeTokenCharacters()
    {
        $allowed = 'abcdefghijklmnopqrstuvwxyz';
        $allowed .= strtoupper($allowed);
        $allowed .= '0123456789';
        //$allowed .= '!§$%&?';
        $this->tokenChars = str_split($allowed);
        shuffle($this->tokenChars);
    }