清除Cookie

   HttpCookie cookies = Request.Cookies[SessionKeys.CookieName];
            if (cookies != null)
            {
                cookies.Expires = DateTime.Today.AddDays(-1);
                Response.Cookies.Add(cookies);
                Request.Cookies.Remove(SessionKeys.CookieName);
            }

https://www.cnblogs.com/shy1766IT/p/3731937.html  用户登录之asp.net cookie的写入、读取与操作