public function getClientFirstMessage()
    {
        /* n: client doesn't support channel binding,
         * <empty>,
         * n=<user>: SASLprepped username with "," and "=" escaped,
         * r=<nonce>: Random nonce */
        $this->_authmsg = 'n=' . str_replace(
            array(',', '='),
            array('=2C', '=3D'),
            $this->_user
        ) . ',r=' . $this->_nonce;

        return 'n,,' . $this->_authmsg;
    }