getAccessToken.js

const fetch = require('node-fetch');
const spotify = require('./credentials');

const getAccessToken = (req, res, next) => {
  const { code } = req.query;

  if (code) {
    const url = 'https://accounts.spotify.com/api/token';

    const data = {
      grant_type: 'authorization_code',
      code,
      redirect_uri: spotify.redirect_uri,
      client_id: spotify.client_id,
      client_secret: spotify.client_secret,
    };

    const headers = {
      'Content-Type': 'application/x-www-form-urlencoded; charset=UTF-8',
    };

    const searchParams = new URLSearchParams();

    Object.keys(data).forEach(prop => {
      searchParams.set(prop, data[prop]);
    });

    fetch(url, {
      method: 'POST',
      headers,
      body: searchParams,
    })
      .then(res => res.json())
      .then(credentials => {
        req.credentials = credentials;
        req.credentials.timestamp = Date.now();
        next();
      })
      .catch(next);
  }
};

module.exports = getAccessToken;