protected function initializeProxyTicket()
    {
        if (!empty($this->_proxyTicket)) {
            throw new CAS_OutOfSequenceException(
                'Already initialized, cannot initialize again.'
            );
        }
        // Allow usage of a particular CAS_Client for unit testing.
        if (empty($this->_casClient)) {
            phpCAS::initializeProxiedService($this);
        } else {
            $this->_casClient->initializeProxiedService($this);
        }
    }