将变量与session (express-session)一起使用- loggedin & username有效，但对其他变量无效

const express = require('express');
const session = require('express-session');
const app = express();

app.use(session({
  secret: 'your-secret-key',
  resave: false,
  saveUninitialized: true
}));

app.post('/login', (req, res) => {
  // 假设通过表单提交获取到了用户名和密码
  const { username, password } = req.body;

  // 验证用户名和密码
  if (username === 'validUsername' && password === 'validPassword') {
    // 登录成功，将相关信息存储到session中
    req.session.loggedin = true;
    req.session.username = username;

    res.send('Login successful');
  } else {
    res.send('Invalid username or password');
  }
});

app.get('/profile', (req, res) => {
  if (req.session.loggedin) {
    const username = req.session.username;
    // 其他变量无效的处理逻辑

    res.send(`Welcome back, ${username}!`);
  } else {
    res.send('Please login first');
  }
});