code

const { request } = require('express');
const express = require('express');
const client_id = "id";
const client_secret = "secret";
const redirect_uri = "http://localhost:3000/callback";

const app = express();

app.get('/login', (req, res) => {
  const scope = 'user-read-private user-read-email';
  const state = Math.random().toString(36).slice(2,18);

  const auth_query_parameters = new URLSearchParams({
    response_type: "code",
    client_id: client_id,
    scope: scope,
    redirect_uri: redirect_uri,
    state: state
  });

  res.redirect('http://accounts.spotify.com/authorize?' +
  auth_query_parameters.toString());
});

app.get('/callback', (req, res) => {
  const code = req.query.code || null;
  const state = req.query.state || null;

  const state_mismatch = new URLSearchParams({
    error: 'state_mismatch'
  });

  if (state == null) {
    res.redirect('/#' +
    state_mismatch.toString());
  }
  else {
    const authOptions = {
      url: 'https://accounts.spotify.com/api/token',
      form: {
        code: code,
        redirect_uri: redirect_uri,
        grant_type: 'authorization_code'
      },
      headers: {
        'Authorization': 'Basic ' + (Buffer.from(client_id + ':' + client_secret).toString('base64')),
        'Content-Type': "application/x-www-form-urlencoded"
      },
      json: true
    };
  }
});

app.listen(3000);