使用express和react框架。前端向后端发送的每个请求都会产生一个新的session，怎么改？

Question

```server.js
 'use strict';

var HTTP_PORT = process.env.PORT || 8080;
var express = require('express');
var path = require('path');
var app = express();
var bodyParser= require('body-parser');
var logger = require('morgan');
var cookieParser = require('cookie-parser');
var mongoose = require('mongoose');
var session = require('express-session');
//https://www.npmjs.com/package/connect-mongo   require it after require the seesion
var connectMongo = require('connect-mongo')(session);
//require passport from: https://github.com/jaredhanson/passport-local

mongoose.Promise = global.Promise;
mongoose.connect('mongodb://localhost:27017/online-cart', { useNewUrlParser: true});
mongoose.set('useCreateIndex', true);

// importing route 

var indexRouter = require('./routes/index');

// module providing Connect/Express middleware
var cors = require('cors'); 

app.use(logger('dev'));
app.use(bodyParser.urlencoded({ extended: false }));
app.use(bodyParser.json());
app.use(cookieParser('ese330')); 
app.use(cors());

// routers(app);

//enable session, save session with a secret key from: http://www.senchalabs.org/connect/session.html
//according to: https://www.npmjs.com/package/express-session,
app.use(session({
    secret: 'ese330',
    resave: false,
    saveUninitialized: false,
    //https://www.npmjs.com/package/connect-mongo  --- Re-use a Mongoose connection already existing before
    store: new connectMongo({ mongooseConnection: mongoose.connection }),
    //session expires after 5 minutes
    cookie: {maxAge: 3600000}
}));

app.use(indexRouter);

app.listen(HTTP_PORT, () => {
    console.log("app listening on: " + HTTP_PORT);
});


router:
router.get('/token',function(req,res,next){

    // res.cookie("token",req.csrfToken(),{maxAge: 900000, httpOnly: true});
    console.log(req.session.id)
    res.status(200).json({message:'oken:req.csrfToken()'});
})
router.put('/user/login',function(req,res){
    var email = req.body.email;
    var password = req.body.password;
    User.findOne({email:email},function(err,user){
        if(err)
        res.status(200).send({code:120,msg:err.message}).end();
        if(!err){
            if(user.passValid(password)){
                req.session.email=email;
                req.session.save()
                console.log(req.session)
                if(email === '[e-mail]'){
                    res.status(200).send({code:1,msg:'manager'})
                }
                else
                res.status(200).send({code:0,msg:'success'})
            }
            else{
                res.status(200).send({code:100,msg:'wrong password'})
            }
        }
    })
})