我创建了一个测试React应用程序，部署在vercel，服务器在render.com。为了解决跨站点cookie问题，我在两个站点上设置了相同的域（app.mydomain.online应用程序为www.example.com，APIapi.mydomain.online）。现在，当我查看标题中的cookie时，没有显示任何错误。但是，cookie仍然没有被存储。
通过npm init创建服务器。通过npm create-react-app创建React。
这是我的示例代码。
伺服器

const express = require("express");
const cors = require("cors");
const session = require('express-session');
const app = express();
require('dotenv').config();

const PORT = process.env.PORT;

app.use(express.json());
app.use(cors({
    origin: 'https://app.myDomain.online',
    methods: ["POST", "PUT", "GET", "OPTIONS", "HEAD"],
    credentials: true
}));

const oneDay = 1000 * 60 * 60 * 24;
app.set('trust proxy', 1) // trust first proxy
app.use(session({
  secret: 'keyboard cat',
  resave: false,
  saveUninitialized: true,
  cookie: { secure: true, sameSite: 'none' }
}));

app.get('/createSession', (req, res) => {
    req.session.user = 'user';
    res.send('new session is created');
});

app.get('/', (req, res) => {
    res.send('get sess')
});

app.get('/getSession', (req, res) => {
    if(req.session.user){
        res.send('active');
    }else{
        res.send('not active');
    }
});

app.listen(PORT, () => {
    console.log(`The server is running on port ${PORT}`);
});

React

import React from 'react'
import { useEffect } from 'react';
import Axios from 'axios';

function Test() {
    
    useEffect(() => {
        Axios.get(' https://api.myDomain.online/createSession',
                  { withCredentials: true }
        );
    }, []);
    
    

    return (
        <div>Test</div>
    )
}

export default Test;