/**

* Copyright 2018 Google Inc.

*

* 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.

*/

const express = require('express');

const PORT = process.env.PORT || 8080;

const {OAuth2Client} = require('google-auth-library');

// Authentication audience (either APP_URL or PROJECT_NUMBER)

const audienceType = 'AUDIENCE_TYPE';

// Intended audience of the token:

// - The URL of the app when audienceType is set to APP_URL

// - The project number when audienceType is set to PROJECT_NUMBER

const audience = 'AUDIENCE';

const client = new OAuth2Client();

const app = express()

.use(express.urlencoded({extended: false}))

.use(express.json());

app.post('/', async (req, res) => {

let text = '';

let authorization = req.headers.authorization;

if (!(await verifyChatAppRequest(authorization.substring('Bearer '.length, authorization.length)))) {

text = 'Failed verification!';

} else if (req.body.type === 'ADDED_TO_SPACE' && req.body.space.type === 'ROOM') {

// Case 1: When App was added to the ROOM

text = `Thanks for adding me to ${req.body.space.displayName}`;

} else if (req.body.type === 'ADDED_TO_SPACE' &&

// Case 2: When App was added to a DM

req.body.space.type === 'DM') {

text = `Thanks for adding me to a DM, ${req.body.user.displayName}`;

} else if (req.body.type === 'MESSAGE') {

// Case 3: Texting the App

text = `Your message : ${req.body.message.text}`;

}

return res.json({text});

});

// Determine whether a Google Chat request is legitimate.

async function verifyChatAppRequest(bearer) {

if (audienceType === 'APP_URL') {

// [START chat_request_verification_app_url]

// Bearer Tokens received by apps will always specify this issuer.

const chatIssuer = 'chat@system.gserviceaccount.com';

// Verify valid token, signed by chatIssuer, intended for a third party.

try {

const ticket = await client.verifyIdToken({

idToken: bearer,

audience: audience

});

return ticket.getPayload().email_verified

&& ticket.getPayload().email === chatIssuer;

} catch (unused) {

return false;

}

// [END chat_request_verification_app_url]

} else if (audienceType === 'PROJECT_NUMBER') {

// [START chat_request_verification_project_number]

// Bearer Tokens received by apps will always specify this issuer.

const chatIssuer = 'chat@system.gserviceaccount.com';

// Verify valid token, signed by CHAT_ISSUER, intended for a third party.

try {

const response = await fetch('https://www.googleapis.com/service_accounts/v1/metadata/x509/' + chatIssuer);

const certs = await response.json();

await client.verifySignedJwtWithCertsAsync(

bearer, certs, audience, [chatIssuer]);

return true;

} catch (unused) {

return false;

}

// [END chat_request_verification_project_number]

}

// Skip verification if audienceType is not set with supported value

return true;

}

app.listen(PORT, () => {

console.log(`Server is running in port - ${PORT}`);

});