处理登录返回跳转链接

def _return_url(self):
        """
            处理登录返回跳转链接
        """
        if type(self).__name__ == "LoginHandler" and self.request.method == "POST":
            return_url = self.get_argument("next", None)
            if return_url: self.set_cookie(self._RETURN_URL, return_url)