app.js

/**
 * Copyright 2019, Google LLC
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *    http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

'use strict';

// [START getting_started_auth_all]
const express = require('express');
const metadata = require('gcp-metadata');
const {OAuth2Client} = require('google-auth-library');

const app = express();
const oAuth2Client = new OAuth2Client();

// Cache externally fetched information for future invocations
let aud;

// [START getting_started_auth_metadata]
async function audience() {
  if (!aud && (await metadata.isAvailable())) {
    let project_number = await metadata.project('numeric-project-id');
    let project_id = await metadata.project('project-id');

    aud = '/projects/' + project_number + '/apps/' + project_id;
  }

  return aud;
}
// [END getting_started_auth_metadata]

// [START getting_started_auth_audience]
async function validateAssertion(assertion) {
  if (!assertion) {
    return {};
  }

  // Check that the assertion's audience matches ours
  const aud = await audience();

  // Fetch the current certificates and verify the signature on the assertion
  // [START getting_started_auth_certs]
  const response = await oAuth2Client.getIapPublicKeys();
  // [END getting_started_auth_certs]
  const ticket = await oAuth2Client.verifySignedJwtWithCertsAsync(
    assertion,
    response.pubkeys,
    aud,
    ['https://cloud.google.com/iap']
  );
  const payload = ticket.getPayload();

  // Return the two relevant pieces of information
  return {
    email: payload.email,
    sub: payload.sub,
  };
}
// [END getting_started_auth_audience]

// [START getting_started_auth_front_controller]
app.get('/', async (req, res) => {
  const assertion = req.header('X-Goog-IAP-JWT-Assertion');
  let email = 'None';
  try {
    const info = await validateAssertion(assertion);
    email = info.email;
  } catch (error) {
    console.log(error);
  }
  res.status(200).send(`Hello ${email}`).end();
});

// [END getting_started_auth_front_controller]

// Start the server
const PORT = process.env.PORT || 8080;
app.listen(PORT, () => {
  console.log(`App listening on port ${PORT}`);
  console.log('Press Ctrl+C to quit.');
});

// [END getting_started_auth_all]

module.exports = app;