How to send email verification after user creation with Firebase Cloud functions?

There are two possibilities to send an "email verification" email to a user:

  1. The signed-in user requests that a verification email be sent. For that, you call, from the front-end, the sendEmailVerification() method from the appropriate Client SDK.
  2. Through one of the Admin SDKs, you generate a link for email verification via the corresponding method (e.g. auth.generateEmailVerificationLink() for the Node.js Admin SDK) and you send this link via an email sent through your own mechanism. All of that is done in the back-end, and can be done in a Cloud Function.

Note that the second option with the Admin SDKs is not exactly similar to the first option with the Client SDKs: in the second option you need to send the email through your own mechanism, while in the first case, the email is automatically sent by the Firebase platform

If you'd like that ability to be added to the Admin SDK, I'd recommend you file a feature request.


This is how I implemented it successfully using Firebase cloud functions along with a small express backend server

Firebase Cloud function (background) triggered with every new user created

  • This function sends a "user" object to your api endpoint

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

// Send email verification through express server
exports.sendVerificationEmail = functions.auth.user().onCreate((user) => {
  // Example of API ENPOINT URL 'https://mybackendapi.com/api/verifyemail/'
  return fetch( < API ENDPOINT URL > , {
      method: 'POST',
      body: JSON.stringify({
        user: user
      }),
      headers: {
        "Content-Type": "application/json"
      }
    }).then(res => console.log(res))
    .catch(err => console.log(err));
});

Server Middleware code

  • verifyEmail here is used as middleware

// File name 'middleware.js'
import firebase from 'firebase';
import admin from 'firebase-admin';

// Get Service account file from firebase console
// Store it locally - make sure not to commit it to GIT
const serviceAccount = require('<PATH TO serviceAccount.json FILE>');
// Get if from Firebase console and either use environment variables or copy and paste them directly
// review security issues for the second approach
const config = {
  apiKey: process.env.APIKEY,
  authDomain: process.env.AUTHDOMAIN,
  projectId: process.env.PROJECT_ID,
};
// Initialize Firebase Admin
admin.initializeApp({
  credential: admin.credential.cert(serviceAccount),
});

// Initialize firebase Client
firebase.initializeApp(config);

export const verifyEmail = async(req, res, next) => {
  const sentUser = req.body.user;
  try {
    const customToken = await admin.auth().createCustomToken(sentUser.uid);
    await firebase.auth().signInWithCustomToken(customToken);
    const mycurrentUser = firebase.auth().currentUser;
    await mycurrentUser.sendEmailVerification();
    res.locals.data = mycurrentUser;
    next();
  } catch (err) {
    next(err);
  }
};

Server code

// Filename 'app.js'
import express from 'express';
import bodyParser from 'body-parser';
// If you don't use cors, the api will reject request if u call it from Cloud functions
import cors from 'cors';
import {
  verifyEmail
} from './middleware'

app.use(cors());
app.use(bodyParser.urlencoded({
  extended: true,
}));
app.use(bodyParser.json());

const app = express();
// If you use the above example for endpoint then here will be
// '/api/verifyemail/'
app.post('<PATH TO ENDPOINT>', verifyEmail, (req, res, next) => {
  res.json({
    status: 'success',
    data: res.locals.data
  });
  next()
})

This endpoint will return back the full user object and will send the verification email to user.

I hope this helps.

Tags:

Email Verification

Firebase

Firebase Authentication

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