public function ensureAuthenticationCallSuccessful()
    {
        $this->_ensureAuthenticationCalled();
        if (!$this->_authentication_caller['result']) {
            throw new CAS_OutOfSequenceException(
                'authentication was checked (by '
                . $this->getAuthenticationCallerMethod()
                . '() at ' . $this->getAuthenticationCallerFile()
                . ':' . $this->getAuthenticationCallerLine()
                . ') but the method returned false'
            );
        }
    }