auth.js

const fs = require('fs');
const readline = require('readline');
const {google} = require('googleapis');

var exports = module.exports = {};

// If modifying these scopes, delete credentials.json.
const SCOPES = [
  'https://www.googleapis.com/auth/script.processes',
  'https://www.googleapis.com/auth/script.projects',
  'https://www.googleapis.com/auth/script.container.ui',
  'https://www.googleapis.com/auth/script.external_request',
  'https://www.googleapis.com/auth/script.deployments',
  'https://www.googleapis.com/auth/spreadsheets',
  'https://www.googleapis.com/auth/drive.metadata.readonly',
  'https://www.googleapis.com/auth/script.webapp.deploy',
  'https://www.googleapis.com/auth/cloud-platform.read-only',
  'https://www.googleapis.com/auth/logging.read',
];
const TOKEN_PATH = "credentials.json";
const CLIENT_SECRET_PATH="client_secret.json";

// Load and return client secrets from a local file
// @param scopes [Array] A list of auth scopes (optional)
// @return {google.auth.OAuth2} An authorized OAuth2 client
exports.authenticate = (scopes = SCOPES) => {
  return new Promise((resolve, reject) => {
    // Load client secrets from a local file.
    fs.readFile(CLIENT_SECRET_PATH, (err, credentials) => {
      if (err) reject(err);
      // Authorize a client with credentials, then call the Google Drive API.
      authorize(scopes, JSON.parse(credentials), resolve)
    });
  })
}

/**
 * Create an OAuth2 client with the given credentials, and then execute the
 * given callback function.
 * @param {Object} credentials The authorization client credentials.
 * @param {function} callback The callback to call with the authorized client.
 */
function authorize(scopes, credentials, callback) {
  const {client_secret, client_id, redirect_uris} = credentials.installed;
  const oAuth2Client = new google.auth.OAuth2(
      client_id, client_secret, redirect_uris[0]);

  // Check if we have previously stored a token.
  fs.readFile(TOKEN_PATH, (err, token) => {
    if (err) return getAccessToken(scopes, oAuth2Client, callback);
    oAuth2Client.setCredentials(JSON.parse(token));
    callback(oAuth2Client);
  });
}

/**
 * Get and store new token after prompting for user authorization, and then
 * execute the given callback with the authorized OAuth2 client.
 * @param {google.auth.OAuth2} oAuth2Client The OAuth2 client to get token for.
 * @param {getEventsCallback} callback The callback for the authorized client.
 */
function getAccessToken(scopes, oAuth2Client, callback) {
  const authUrl = oAuth2Client.generateAuthUrl({
    access_type: 'offline',
    scope: scopes,
  });
  console.log('Authorize this app by visiting this url:', authUrl);
  const rl = readline.createInterface({
    input: process.stdin,
    output: process.stdout,
    terminal: false
  });
  rl.question('Enter the code from that page here: ', (code) => {
    rl.close();
    oAuth2Client.getToken(code, (err, token) => {
      if (err) return callback(err);
      oAuth2Client.setCredentials(token);
      // Store the token to disk for later program executions
      fs.writeFile(TOKEN_PATH, JSON.stringify(token), (err) => {
        if (err) console.error(err);
        console.log('Token stored to', TOKEN_PATH);
      });
      callback(oAuth2Client);
    });
  });
}