I am trying to make a post message to the /users/signup end and this error occurs every time.
Here is my code from server.js

const https = require('https');

const fs = require('fs');

var path = require('path');

const  mongoose = require('mongoose');

const express = require('express');

var cors = require('cors') //

var session = require('express-session');

var FileStore = require('session-file-store')(session); // data base for storing information about sessions.

var cookieParser = require('cookie-parser');

var logger = require('morgan'); // gia ta htpp errors, requests logger

mongoose.set('useFindAndModify', false);

mongoose.set('useUnifiedTopology',true);

const url = 'mongodb://localhost:27017/database';

mongoose.set('useNewUrlParser',true);

mongoose.set('useCreateIndex',true);

mongoose.connect(url)



.then(connection => {

  console.log('Connected to MongoDB DB')

})

.catch(error => {

console.log(error.message)

})

var app = express();

app.use(cors());

var passport = require('passport');

var authenticate = require('./authenticate');

const usersRouter = require('./routes/users');

const options = {

  key: fs.readFileSync('./key.pem','utf8'),

  cert: fs.readFileSync('./server.crt','utf8')

};



app.use(function(req, res, next) { // kolpa magkiorika poy de ta kserw

    res.header("Access-Control-Allow-Origin", "*");

    res.header("Access-Control-Allow-Headers", "Origin, X-Requested-With, Content-Type, Accept, Access-Control-Allow-Headers, Access-Control-Request-Method, Access-Control-Request-Headers, Authorization");

    res.header('Access-Control-Allow-Methods', 'GET, PUT, POST, DELETE, PATCH, OPTIONS');

    next();

});

app.set('views', path.join(__dirname, 'views'));

app.set('view engine', 'jade');

app.use(logger('dev'));

app.use(express.json());

app.use(express.urlencoded({ extended: false }));



app.use(session({

  name: 'session-id',

  secret: '12345-67890-09876-54321', // digital sign for cookie.( Server secret key to sign the cookie)

  saveUninitialized: false,

  resave: false,

  store: new FileStore(({logFn: function(){}}))

}));

app.use(passport.initialize());

app.use(passport.session());



app.use('/users',usersRouter);



function auth (req, res, next) {

  if (!req.user) {

    var err = new Error('You are not authenticated!');

    err.status = 403;

    return next(err);

  }

  else {

        next();

  }

}

app.use(auth);

const port = 8000;

server = https.createServer(options, app).listen(port, function(){

    console.log(`Server started on port ${port}`);

});

 //error  handler 

module.exports = server;

I have add lines of code to allow cors on requests but the error keep exists. When i am using postman everything works fine, and the cors headers are in the response headers.

Here it is , the Register Component

import React, { Component,useState } from 'react';

import '../css/Register.css';

import axios from 'axios';

import {withRouter} from 'react-router';

import url from '../services/url';



class Register extends Component{

    constructor(props){

        super(props);

        this.state = {

            username: "",

            password: "",

            password2: "",

            phone: "",

            email: "",

            userType: ""

        };

        this.handleChange = this.handleChange.bind(this);

        this.handleSubmit = this.handleSubmit.bind(this);

    }



    handleChange(event) {

        this.setState({ [event.target.name]: event.target.value })

    }



    handleSubmit = async event => {

      event.preventDefault();

        

        if(this.state.password === this.state.password2){

            try {

                const response = await fetch(`https://localhost:8000/users/signup`, {

                    method: 'POST',

                    mode: 'cors',

                    headers: {

                        'Content-Type': 'application/json',

                    },

                    body: JSON.stringify({

                        username: this.state.username,

                        password: this.state.password,

                        phone: this.state.phone,

                        email: this.state.email,

                        userType: this.state.userType



                    })

                })

                const jsoned = await response.json();

            } catch (error) {

                console.log(error);

                console.log('asdfasfasfa');

            }

        }else{

            alert('passwords do not match')

        }    

  };

render(){

      .... html code..

    }

export default withRouter(Register);

And the full error message

Cross-Origin Request Blocked: The Same Origin Policy disallows reading the remote resource at https://localhost:8000/users/signup. (Reason: CORS request did not succeed).
TypeError: NetworkError when attempting to fetch resource.

the signup route.

router.post('/signup', (req, res, next) => {

  User.register(new User({username: req.body.username, email:req.body.email, phone:req.body.phone, userType:req.body.userType}), 

    req.body.password, (err, user) => {

    if(err) {

      console.log(err)

      res.statusCode = 500;

      res.setHeader('Content-Type', 'application/json');

      res.json({err: err});

    }

    else {

      passport.authenticate('local')(req, res, () => {

        res.statusCode = 200;

        res.setHeader('Content-Type', 'application/json');

        res.json({success: true, status: 'Registration Successful!'});

      });

    }

  });

});

Request headers when i send post request

OPTIONS /users/signup HTTP/1.1

Host: localhost:8000

User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:88.0) Gecko/20100101 Firefox/88.0

Accept: */*

Accept-Language: en-US,en;q=0.5

Accept-Encoding: gzip, deflate, br

Access-Control-Request-Method: POST

Access-Control-Request-Headers: content-type

Referer: http://localhost:3000/

Origin: http://localhost:3000

Connection: keep-alive