'Add a MAC token to the request authorization header.
Warning: MAC token support is experimental as the spec is not yet stable.'

def _add_mac_token(self, uri, http_method=u'GET', body=None, headers=None, token_placement=AUTH_HEADER, ext=None, **kwargs):

    headers = tokens.prepare_mac_header(self.access_token, uri, self.mac_key, http_method, headers=headers, body=body, ext=ext, hash_algorithm=self.mac_algorithm, **kwargs)
    return (uri, headers, body)
