def post(self, uri, data, params=dict()):
        """POST the serialized XML to the given URI.
        Return the response XML as an ElementTree.
        """
        r = requests.post(uri, data=data, params=params,
                          auth=(self.username, self.password),
                          headers={'content-type': 'application/xml',
                                   'accept': 'application/xml'})
        return self.parse_response(r, accept_status_codes=[200, 201, 202])