求助 - express3.0 csrf 问题，在线等

        //cookie
        app.use(express.cookieParser());
        //session
        app.use(express.session({
            secret:config.session_secret,
            store: new mongoStore({
                url: config.mongodb,
                collection : 'sessions'
            })
        }));

        app.use(express.csrf());

        app.use(function(req, res, next){
            res.locals.req = req;
            res.locals.session = req.session;
            res.locals.csrf = req.session ? req.session._csrf : ''
            next();
        });

我的_csrf一直在变化着的呢？我看cnodejs网站和其他网站，都没变化，求解。。 req.session._csrf is deprecated, use req.csrfToken([callback]) instead