什么应该是凭据的HTTP状态代码过期的错误/异常？

I am developing RESTful APIs, I have implemented token-based authentication, where token digest is prepared using time-stamp. Now when request comes to API server, I am checking if the supplied time-stamp is invalid ( i.e. date-time from future/past is specified) then am throwing error message indicating that "future token detected" or "token has expired". I need to attach HTTP status code I am confused about which status code is suitable for this situation?I am developing RESTful APIs, I have implemente