public function setCasServerCACert($cert, $validate_cn)
    {
    // Argument validation
        if (gettype($cert) != 'string') {
            throw new CAS_TypeMismatchException($cert, '$cert', 'string');
        }
        if (gettype($validate_cn) != 'boolean') {
            throw new CAS_TypeMismatchException($validate_cn, '$validate_cn', 'boolean');
        }
        if ( !file_exists($cert) && $this->_requestImplementation !== 'CAS_TestHarness_DummyRequest'){
            throw new CAS_InvalidArgumentException("Certificate file does not exist " . $this->_requestImplementation);
        }
        $this->_cas_server_ca_cert = $cert;
        $this->_cas_server_cn_validate = $validate_cn;
    }