express 4.x 打开网页时弹出登录对话框

//打开网页时弹出登录对话框app.use(function(req, res, next) {    var auth = req.headers['authorization'];    if(auth) {        var tmp = auth.split(' ');        var buf = new Buffer(tmp[1], 'base64');        var plain_auth = buf.toString();        var creds = plain_auth.split(':');        var username = creds[0];        var password = creds[1];        if((username == 'admin') && (password == 'admin')) {            //认证成功，允许访问            return next();        }    }    //要让浏览器弹出登录对话框，必须将status设为401，Header中设置WWW-Authenticate    res.set('WWW-Authenticate', 'Basic realm=""');    res.status(401).end();});