auth.js

const fs = require('fs');
const path = require('path');
const { google } = require('googleapis');
const SCOPES = ['https://www.googleapis.com/auth/calendar'];
const TOKEN_PATH = path.join(__dirname, 'token.json');
function authorize() {
  const credentials = JSON.parse(fs.readFileSync('credentials.json'));
  const { client_secret, client_id, redirect_uris } = credentials.installed;
  const oAuth2Client = new google.auth.OAuth2(client_id, client_secret, redirect_uris[0]);
  if (fs.existsSync(TOKEN_PATH)) {
    const token = fs.readFileSync(TOKEN_PATH);
    oAuth2Client.setCredentials(JSON.parse(token));
    return oAuth2Client;
  } else {
    return getAccessToken(oAuth2Client);
  }
}
function getAccessToken(oAuth2Client) {
  const authUrl = oAuth2Client.generateAuthUrl({
    access_type: 'offline',
    scope: SCOPES,
  });
  console.log('Authorize this app by visiting this url:', authUrl);
  // User should visit the above URL and paste the code here:
  const rl = readline.createInterface({
    input: process.stdin,
    output: process.stdout,
  });
  rl.question('Enter the code from that page here: ', (code) => {
    rl.close();
    oAuth2Client.getToken(code, (err, token) => {
      if (err) return console.error('Error retrieving access token', err);
      oAuth2Client.setCredentials(token);
      fs.writeFileSync(TOKEN_PATH, JSON.stringify(token));
      console.log('Token stored to', TOKEN_PATH);
    });
  });
}
module.exports = authorize;