Google Functions code for generating Google Auth tokens

google-auth-functions.js

// Code to write Google API Oauth tokens to Firebase database

const FUNCTIONS_CLIENT_ID = functions.config().googleapi.client_id;
const FUNCTIONS_SECRET_KEY = functions.config().googleapi.client_secret;
const FUNCTIONS_REDIRECT = '{YOUR_FUNCTIONS_SUBDOMAIN}.cloudfunctions.net/OauthCallback';
// TODO: use firebase functions:config:set to configure your Google API client ID and secret
// Also update FUNCTIONS_REDIRECT

const googleAuth = require('google-auth-library');

const auth = new googleAuth();
const functionsOauthClient = new auth.OAuth2(FUNCTIONS_CLIENT_ID, FUNCTIONS_SECRET_KEY,
  FUNCTIONS_REDIRECT);

const SCOPES = ['https://www.googleapis.com/auth/spreadsheets'];

// visit the URL for this Function to obtain tokens
exports.authGoogleAPI = functions.https.onRequest((req, res) =>
  res.redirect(functionsOauthClient.generateAuthUrl({
    access_type: 'offline',
    scope: SCOPES,
    prompt: 'consent'
  }))
);

// after you grant access, you will be redirected to the URL for this Function
// this Function stores the tokens to your Firebase database
const DB_TOKEN_PATH = '/api_tokens';
exports.OauthCallback = functions.https.onRequest((req, res) => {
  const code = req.query.code;
  functionsOauthClient.getToken(code, (err, tokens) => {
    // Now tokens contains an access_token and an optional refresh_token. Save them.
    if (err) {
      return res.status(400).send(err);
    }
    return db.ref(DB_TOKEN_PATH).set(tokens).then(() => res.status(200).send('OK'));
  });
});