错误：引发了跨域错误。错误：应该设置一个秘密

Question

我正在学习制作电子商务网站的课程，当我尝试注册用户时，我收到此错误： 讲师克隆了我的存储库并没有收到任何错误，但是每当我尝试注册或登录时都会收到错误消息。

我该如何解决这个问题？任何帮助将非常感激。也许我用来处理错误的 errorHandler 文件存在问题。

控制器/auth.js

const User = require('../models/user')
const jwt = require('jsonwebtoken') // to generate signed token
const expressJwt = require('express-jwt') // for authorization check
const { errorHandler } = require('../helpers/dbErrorHandler')

exports.signup = (req, res) => {
    console.log("req.body", req.body)
    // signs up new user
 const user = new User(req.body)
 user.save((err, user) => {
if(err) {
    return res.status(400).json({
        err: errorHandler(err)
    })
}
user.salt = undefined 
user.hashed_password = undefined

res.json({
    user 
 })
 })
}

exports.signin = (req, res) => {
// find user based on email
const { email, password } = req.body 
User.findOne({email}, (err, user) => {
if (err || !user) {
    return res.status(400).json({
        error: 'User with that email does not exist.'
    })
}
// if user is found, ensure email & password match
// create authenticate method in user model
if (!user.authenticate(password)) {
    return res.status(401).json({
error: 'Email and password dont match'
    })
}
// generate signed token with user id and secret
const token = jwt.sign({_id: user._id}, process.env.JWT_SECRET)

// persist token as 't' in cookie with expiry date
res.cookie('t', token, {expire: new Date() + 9999 })

// return response with user & token to frontend client
const {_id, name, email, role} = user
return res.json({token, user: {_id, email, name, role}})
})
}

exports.signout = (req, res) => {
    res.clearCookie('t')
    res.json({ message: "Signout success" })
}

exports.requireSignin = expressJwt({
secret: process.env.JWT_SECRET,
userProperty: 'auth'
})

exports.isAuth = (req, res, next) => {
    let user = req.profile && req.auth && req.profile._id == req.auth._id
if(!user) {
    return res.status(403).json({
        error: "Access denied"
    })
}
    next()
}

exports.isAdmin = (req, res, next) => {
    if (req.profile.role === 0) {
        return res.status(403).json({
        error: 'Admin resource! Access denied'
        })
    }
    next()
}

控制台中的错误消息：

  throw new MongooseError('The `uri` parameter to `openUri()` must be a ' +
    ^
Error [MongooseError]: The `uri` parameter to `openUri()` must be a string, got "undefined". Make sure the first parameter to `mongoose.connect()` or `mongoose.createConnection()` is a string.