:param req: object with httplib.Request interface
            Actually, it have to have `url` and `headers` attributes

def get_cookie_header(self, req):
        """
        :param req: object with httplib.Request interface
            Actually, it have to have `url` and `headers` attributes
        """
        mocked_req = MockRequest(req)
        self.cookiejar.add_cookie_header(mocked_req)
        return mocked_req.get_new_headers().get('Cookie')