def joinSite(self, machineAdminUrl,
                 username, password):
        """
        The joinSite operation connects a portal machine to an existing
        site. You must provide an account with administrative privileges to
        the site for the operation to be successful.
        """
        params = {
            "machineAdminUrl" : machineAdminUrl,
            "username" : username,
            "password" : password,
            "f" : "json"
        }
        url = self._url + "/joinSite"
        return self._post(url=url, param_dict=params)