express框架无法获取自定义header信息

在route的过滤器里统一获取令牌信息

router.use(function (req, res, next) {

    res.header("Access-Control-Allow-Origin", "*");
    res.header("Access-Control-Allow-Headers", "Content-Type, Authorization,token, X-Requested-With");
    res.header("Access-Control-Allow-Methods", "PUT,POST,GET,DELETE,OPTIONS");
    res.header("Content-Type", "application/json;charset=utf-8");

    var Authorization = req.headers['Authorization'];//undefined
    var token = req.headers['token']//undefined
    }

    next()
});

以下是客户端请求

 $(function () {
            $.ajax({
                type: "get",
                url: "http://localhost:8081/account/list",
                dataType: "json",
                ContentType: "application/json",
                beforeSend: function (XMLHttpRequest) {
                    XMLHttpRequest.setRequestHeader("token", "fsddfsd");
                    XMLHttpRequest.setRequestHeader("Authorization", "fdfdds");
                }
            });
        });

同样的客户端，用.NET试过能获取到自定义的信息，然而用node.js则是undefined，为何？？