如何在路由之前调用函数以及在函数完成时更改路由

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

// 前置中间件
function authenticate(req, res, next) {
  if (req.headers.authorization === 'Bearer mytoken') {
    // 身份验证成功，继续执行下一个中间件或路由处理程序
    next();
  } else {
    // 身份验证失败，重定向到登录页面
    res.redirect('/login');
  }
}

// 路由处理程序
app.get('/protected', authenticate, (req, res) => {
  res.send('This is a protected route');
});

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

app.listen(3000, () => {
  console.log('Server is running on port 3000');
});

async function asyncMiddleware(req, res, next) {
  try {
    await someAsyncOperation();
    next();
  } catch (error) {
    next(error);
  }
}

app.use((err, req, res, next) => {
  console.error(err.stack);
  res.status(500).send('Something broke!');
});