this was an example of sending up an axios post from react which we could then use on the express side to send back some kind of authenticated response

api.js

const express = require('express')
const cors = require('cors')

const app = new express()
const port = 5000

app.use(cors())
app.use(express.json())

app.get('/api', (req, res) => {
    return res.send({message: 'this is the response'})
})

app.post('/api', (req, res) => {
    const { username } = req.body
    const { password } = req.body
    return res.send({message: 'i got your post request'})
})

app.post('/api/auth', (req, res) => {
    const { username } = req.body
    const { password } = req.body
    if (username === 'harrisonmalone' && password === 'password') {
        return res.send('you are authed')
    }
    else {
        return res.send('you are not authorized')
    }
})

app.listen(port, () => {
    console.log('listening to port 5000')
})

App.js

import React, { Component } from 'react';
import axios from 'axios';
import './App.css';

const authRequest = axios.create({
  baseURL: 'http://localhost:5000/api',
  headers: {
    username: 'harrisonmalone',
    password: '123456'
  }
})

class App extends Component {

  componentDidMount() {
    // fetch('http://localhost:5000/api')
    //   .then((res) => {
    //     return res.json()
    //   })
    //   .then((json) => {
    //     console.log(json)
    //   })
    // can now use authRequest.get()
    axios.get('http://localhost:5000/api')
      .then((res) => console.log(res))
  }

  handlePost() {
    const user = {
      username: 'harrisonmalone',
      password: 'password' 
    }
    console.log('clicked')
    // can now use authRequest.post('', user)
    axios.post('http://localhost:5000/api', user)
      .then((res) => console.log(res.data))
  }

  handleAuth() {
    const user = {
      username: 'harrisonmalone',
      password: 'password' 
    }
    // can now use authRequest.post('/auth', user)
    axios.post('http://localhost:5000/api/auth', user)
    .then((res) => console.log(res.data))
  }

  render() {
    return (
      <div>
        <button onClick={this.handlePost}>Make post request</button>
        <button onClick={this.handleAuth}>Make auth post request</button>
      </div>
    );
  }
}

export default App;