json

Badgeyay is an open source project developed by FOSSASIA Community for generating badges for conferences and events. The Project is divided into two parts frontend, which is in ember, and backend, which is in flask. Backend uses firebase admin SDK (Python) and Frontend uses firebase javascript client with emberfire wrapper for ember. Whenever an user signs up on the website, database listener that is attached to to the Model gets triggered and uses flask-mail for sending welcome mail to the user and in case of email and password signup, verification mail as well.

Problem is sending mail using libraries is a synchronous process and takes a lot of processing on the server. We can use messaging queues like RabbitMQ and Redis but that will be burden as server cost will increase. The workaround is to remove the code from the server and create a firebase cloud function for the same task.

Firebase cloud functions lets you run backend code on the cloud and can be triggered with HTTP events or listen for the events on the cloud, like user registration.

Procedure

1. Firebase uses our Gmail ID for login, so make sure to have a Gmail ID and on the first sight we will be greeted with Firebase console, where we can see our created or imported firebase apps.

2. Create the app by clicking on the Add Project Icon and write the name of the application (e.g. Test Application) and select the region, in my case it is India. Firebase will automatically generated an application ID for the app. Click on Create Project to complete creation of project

   

3. After Completion, click on the project to enter into the project. You will be greeted with an overview saying to integrate firebase with your project. We will click on the Add Firebase to web App and save the config as JSON in a file as clientKey.json for later use.

4. Now we need to install the firebase tools on our local machine so for that execute

npm i -g firebase-tools

5. Now login from the CLI so that firebase gets token for the Gmail ID of the user and can access the firebase account of that Gmail ID.

firebase login

6. After giving permissions to the firebase CLI from your Gmail account in the new tab opened in browser, create a folder named cloud_functions in the project directory and in that execute

firebase init

7. Select only functions from the list of options by pressing space.

   

8. After this select the project from the list where you want to use the cloud function. You can skip the step if you later want to add the cloud function to project by selecting don’t setup a default project and can later be used by command

firebase use --add

9. Choose the language of choice

   

10. If you want, you can enforce eslint on the project and after this the cloud function is set up and the directory structure looks as follows.

    

11. We will write our cloud function in index.js. So let’s take a look at index.js

const functions = require('firebase-functions');

// // Create and Deploy Your First Cloud Functions
// // https://firebase.google.com/docs/functions/write-firebase-functions
//
// exports.helloWorld = functions.https.onRequest((request, response) => {
// response.send("Hello from Firebase!");
// });

As we can see there is a sample function already given, we don’t need that sample function so we will remove it and will write the logic for sending mail. Before that we need to acquire the key for service accounts so that admin functionality can be accessed in the cloud function. So for that go to project settings and then service accounts and click on Generate New Private Key  and save it as serviceKey.json

12. Now the directory structure will look like this after adding the clientKey.json and serviceKey.json

    

13. We will use node-mailer for sending mails in cloud functions and as there is a limitation on the gmail account to send only 500 mails in a day, we can use third party services like sendGrid and others for sending mails with firebase. Configure node-mailer for sending mails as

const nodemailer = require('nodemailer');

const gmailEmail = functions.config().gmail.email;
const gmailPassword = functions.config().gmail.password;
const mailTransport = nodemailer.createTransport({
service: 'gmail',
auth: {
user: gmailEmail,
pass: gmailPassword
}
});

Also set the environment variables for the cloud functions like email and password:

firebase functions:config:set gmail.email="Email ID" gmail.password="Password"

14. Logic for sending Greeting Mail on user registration

exports.greetingMail = functions.auth.user().onCreate((user) => {
const email = user.email;
const displayName = user.displayName;

return sendGreetingMail(email, displayName);
});

function sendGreetingMail(email, displayName) {
const mailOptions = {
from: `${APP_NAME}<noreply@firebase.com>`,
to: email,
};

mailOptions.subject = `Welcome to Badgeyay`;
mailOptions.text = `Hey ${displayName || ''}! Welcome to Badgeyay. We welcome you onboard and pleased to offer you service.`;
return mailTransport.sendMail(mailOptions).then(() => {
return console.log('Welcome mail sent to: ', email)
}).catch((err) => {
console.error(err.message);
});
}

Function will get triggered on creation of user in firebase and calls the greeting mail function with parameters as the email id of the registered user and the Display name. Then a default template is used to send mail to the recipient and Logged on successful submission.

15. Currently firebase admin sdk doesn’t support the functionality to send verification mail but the client SDK does. So the approach which is followed in badgeyay is that admin SDK will create a custom token and client sdk will use that custom token to sign in and them send verification mail to the user.

exports.sendVerificationMail = functions.auth.user().onCreate((user) => {
const uid = user.uid;
if (user.emailVerified) {
console.log('User has email already verified: ', user.email);
return 0;
} else {
return admin.auth().createCustomToken(uid)
.then((customToken) => {
return firebase.auth().signInWithCustomToken(customToken)
})
.then((curUser) => {
return firebase.auth().onAuthStateChanged((user_) => {
if (!user.emailVerified) {
user_.sendEmailVerification();
return console.log('Verification mail sent: ', user_.email);
} else {
return console.log('Email is already verified: ', user_.email);
}
})
})
.catch((err) => {
console.error(err.message);
})
}
});

16. Now we need to deploy the functions to firebase.

firebase deploy --only functions

Link to the respective PR  : Link

Topics Involved

• Firebase Admin SDK
• Configuring Gmail for third party apps
• Token Verification and verification mail by client SDK
• Nodemailer and Express.js

Resources

• Firebase Cloud functions – Link
• Extending authentication with cloud function – Link
• Custom Token Verification – Link
• Nodemailer message configuration – Link
• Issue discussion on sending verification mail with admin SDK – Link