Nodejs CORS 策略：没有“Access-Control-Allow-Origin”header 出现在请求的资源上。当使用 Google OAUTH [重复]

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这个问题在这里已经有了答案：

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找不到 cors 错误的原因我在文件中使用了 cors()。
错误：在 'https://accounts.google.com/o/oauth2/v2/auth?response_type=code&redirect_uri=http%3A%2F%2Flocalhost%3A5000%2Fauth%2Fgoogle%2Fcallback&scope=profile%20email&client_id=812244 访问 XMLHttpRequest -pitcdn033bj4gr2sedv0uknb3tkhs3u9.apps.googleusercontent.com' （重定向自 'http://localhost:5000/auth/google'）来自源 'http://localhost:4200' 已被 CORS 政策阻止：否 'Access-Control- Allow-Origin' header 存在于请求的资源上。

index.js

const express = require('express');
const bodyParser = require('body-parser'); 
const cors = require('cors');

const userRoutes = require('./routes/user.routes');
const authRoutes = require('./routes/auth.routes');

const app = express();
const MAX_UPLOAD_SIZE = '10mb';

app.use(cors());

app.use(bodyParser.json({limit:MAX_UPLOAD_SIZE}));
app.use(bodyParser.urlencoded({extended:true, limit:MAX_UPLOAD_SIZE}))

app.use(errorLogger);

app.use(authRoutes);
app.use(userRoutes);


const PORT = process.env.PORT || 5000;
app.listen(PORT);

auth.routes 文件

const passport = require("passport");
const cors = require('cors');


const AuthService = require("../service/auth.service");

const authRouter = express.Router();
require('../service/auth.service')


authRouter.use(passport.initialize());

authRouter.get('/auth/google',passport.authenticate('google', { scope: ['profile' , 'email'] }));

authRouter.get('/auth/google/callback', 
  passport.authenticate('google', { failureRedirect: '/login' }),
  function(req, res) {
    res.setHeader(200).send('SUCCESS');
  });


module.exports = authRouter;

auth.service 文件

const passport = require('passport');
const GoogleStrategy = require('passport-google-oauth20').Strategy;
const facebookStrategy = require('passport-facebook').Strategy



passport.serializeUser(function(user, cb) {
  cb(null, user);
});

passport.deserializeUser(function(obj, cb) {
  cb(null, obj);
});


passport.use(new GoogleStrategy({
    clientID: "ID",
    clientSecret: "SECRET",
    callbackURL: "http://localhost:5000/auth/google/callback"
  },
  function(accessToken, refreshToken, profile, done) {

    return done(null, profile);
  }
));