How to solve CORS error when using with React, Axios, Express?

Question

I am making simple twitter login using passport js, but when calling twitter route, I get CORS error.

server.js

const express = require("express");
const session = require("express-session");
const dotenv = require("dotenv");
const userLoginRoutes = require("./routes/userLoginRoute");
const cors = require("cors");
const app = express();

app.use(cors());
app.use(function (req, res, next) {
  res.header(
    "Access-Control-Allow-Origin",
    "*"
  ); // update to match the domain you will make the request from
  res.header(
    "Access-Control-Allow-Headers",
    "Origin, X-Requested-With, Content-Type, Accept"
  );
  next();
});
app.get("/api/auth/twitter", passport.authenticate("twitter"));

action dispatching here

import {
  USER__LOGIN,
  USER__LOGIN__FAILURE,
  USER__LOGIN__SUCCESS,
} from "../constants/loginconstants";

const axios = require("axios");

// login action
export const userLoginAction = () => async (dispatch) => {
  try {
    dispatch({
      type: USER__LOGIN,
    });
    const config = {
      header: {
        "Content-Type": "application/json",
        "Access-Control-Allow-Origin" : "*"
      },
    };
    const { data } = await axios.get(`/api/auth/twitter`, config);
    dispatch({
      type: USER__LOGIN__SUCCESS,
      payload: data,
    });
  } catch (error) {
    dispatch({
      type: USER__LOGIN__FAILURE,
      payload:
        error.response && error.response.data.message
          ? error.response.data.message
          : error.message,
    });
  }
};

in package.json in client,

  "proxy": "http://127.0.0.1:3001",

Also I cannot see Access-Control-Allow-Origin in the network tab, see here,

Is there anything wrong while setting the Access-Control-Allow-Origin?

I cannot figure out, where am I getting wrong. I have used cors, and even manually set the origin to *.

Cors error that i am getting,