public function setPostBody ($body)
    {
        if ($this->_sent) {
            throw new CAS_OutOfSequenceException(
                'Request has already been sent cannot '.__METHOD__
            );
        }
        if (!$this->isPost) {
            throw new CAS_OutOfSequenceException(
                'Cannot add a POST body to a GET request, use makePost() first.'
            );
        }

        $this->postBody = $body;
    }