How to Build A Passwordless Authentication with Email and JWTby@FlippedCoding
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How to Build A Passwordless Authentication with Email and JWT

by MileciaApril 27th, 2021
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There are a few different types of authentication methods you can choose from: session-based, token-based and passwordless. Each of these authentication methods has its pros and cons and we'll go over a few of them. With passwordless authentication, there is no need for credentials to log in. All you need is an email address or phone number associated with an account and you will get a magic link or one-time password each time you want to log into the app. We'll use some basic HTML and JavaScript to make the front-end user interface code.

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Broken authentication is the second highest security risk for web applications. This usually means that session management and authentication aren't handled correctly. This gives attackers several avenues to get access to data they can use maliciously.

That's why it is important to make sure you get the best practices in place as early in the development process as possible. You can do a few things to make your authentication process more secure and protect your users. We'll go over a few of those things with a quick Node.js app.

First, let's go over some of the different ways you can handle authentication.

Authentication methods

There are a few different types of authentication methods you can choose from: session-based, token-based, and passwordless. Each of these authentication methods has its pros and cons and we'll go over a few of them.

Session-based authentication

This is the most common form of authentication. It only requires a username and password that match what's in a database. If a user enters the correct set of login credentials, they will have a session initialized for them with a specific ID. A session is typically ended when a user logs out of the app.

When sessions are implemented correctly, they will automatically expire after a set amount of time. You'll see this a lot in finance apps, like banking and trading. This gives users an added layer of security in case they've logged into their bank account on a public computer and forgot about that tab.

Token-based authentication

Instead of using actual credentials to authenticate requests, token-based authentication gives users a temporary token that's stored in the browser. This token is typically a JWT (JSON Web Token) that contains all of the information an endpoint will need to validate a user.

Every request that a user makes will include that token. One of the benefits to using a token is that they can have embedded information about what roles and permissions a user might have without fetching that data from a database. This gives attackers less access to critical information, even if they are able to steal a user's token.

Passwordless authentication

This form of authentication is completely different from the others. There is no need for credentials to log in. All you need is an email address or phone number associated with an account and you will get a magic link or one-time password each time you want to log in. As soon as you click the link, you'll get redirected to the app and you'll already be logged in. After that, the magic link isn't valid so no one else can use it.

When the magic link is generated, a JWT is also generated with it. This is how the authentication happens. With this login method, it's a lot harder for attackers to hack their way into your system. There are fewer inputs for them to take advantage of and sending the JWT through the magic link makes them harder to intercept than sending them through a response.

Now that you know about these different authentication methods, let's implement a passwordless authentication model.

Implementing authentication in Node

Passwordless authentication flow

We'll start by going through the process flow of passwordless authentication.

  • A user submits their email address or phone number in the web app.
  • They are sent a magic link to log in with.
  • The user clicks the magic link and they are redirected to the app, already logged in.

Now that we have the flow we need to implement, let's start by making a super basic front-end.

Front-end setup

We don't even need to use a JavaScript framework since the focus is mostly on the back-end. So we'll use some basic HTML and JavaScript to make the front-end.

Here's what the user interface code will be. Just a small HTML file that uses a frontend.js file.

<!DOCTYPE html>
        <title>Passwordless Authentication</title>
        <script src="./frontend.js"></script>
        <h1>This is where you'll put your email to get a magic link.</h1>
                <label for="email_address">Enter your email address</label>
                <input type="email" id="email_address" />
            <button type="submit" id="submit_email">Get magic link</button>

This is what the frontend.js file will look like.

window.onload = () => {
  const submitButton = document.getElementById("submit_email");
  const emailInput = document.getElementById("email_address")
  submitButton.addEventListener("click", handleAuth);
  /** This function submits the request to the server for sending the user a magic link.
   * Params: email address
   * Returns: message
  async function handleAuth() {
    const message = await"http://localhost:4300/login", {
      email: emailInput.value
    return message;

The JavaScript file gets the submit button we made in the HTML file and adds a click event listener to it. So when the button is clicked, we'll make a POST request to the server we have running on

at the
endpoint with the email address entered. Then, if the POST request is successful, we will get a message back we can show to the user.

Back-end setup

Now we're going to start making our Node app. We'll start by making an express app and installing a few packages.

import cors from "cors";
import express from "express";

const PORT = process.env.PORT || 4000;
const app = express();

// Set up middleware
app.use(express.urlencoded({ extended: false }));

// Login endpoint"/login", (req, res) => {
  const email =;

  if (!email) {
      message: "There is no email address that matches this.",

  if (email) {

// Start up the server on the port defined in the environment
const server = app.listen(PORT, () => {"Server running on port " + PORT)

export default server

With this basic server in place, we can start adding more functionality. Let's go ahead and add the email service we're going to use. First, add nodemailer to your package.json and then import it.

import nodeMailer from "nodemailer";

Then below the middleware, we'll make a transporter to send emails. This code configures nodemailer and makes the email template with some simple HTML.

// Set up email
const transport = nodeMailer.createTransport({
  host: process.env.EMAIL_HOST,
  port: 587,
  auth: {
      user: process.env.EMAIL_USER,
      pass: process.env.EMAIL_PASSWORD

// Make email template for magic link
const emailTemplate = ({ username, link }) => `
  <h2>Hey ${username}</h2>
  <p>Here's the login link you just requested:</p>

Next, we need to make our token that holds the user's info. This is just an example of some of the basic things you might include in a token. You could also include things like, user permissions, special access keys, and other information that might be used in your app.

// Generate token
const makeToken = (email) => {
  const expirationDate = new Date();
  expirationDate.setHours(new Date().getHours() + 1);
  return jwt.sign({ email, expirationDate }, process.env.JWT_SECRET_KEY);

Now we can update the

endpoint to send a magic link to registered users and they'll be logged in to the app as soon as they click it.

// Login endpoint"/login", (req, res) => {
  const { email } = req.body;
  if (!email) {
      message: "You didn't enter a valid email address.",
  const token = makeToken(email);
  const mailOptions = {
    from: "You Know",
    html: emailTemplate({
      link: `http://localhost:8080/account?token=${token}`,
    subject: "Your Magic Link",
    to: email,
  return transport.sendMail(mailOptions, (error) => {
    if (error) {
      res.send("Can't send email.");
    } else {
      res.send(`Magic link sent. : http://localhost:8080/account?token=${token}`);

There are only two more things we need to add to the code to get the server finished. Let's add an

endpoint. Then we'll add a simple authentication method.

// Get account information
app.get("/account", (req, res) => {
  isAuthenticated(req, res)

This gets the user's token from the front-end and calls the authentication function.

const isAuthenticated = (req, res) => {  const { token } = req.query
  if (!token) {
    res.send("Can't verify user.")
  let decoded
  try {
    decoded = jwt.verify(token, process.env.JWT_SECRET_KEY)
  catch {
    res.send("Invalid auth credentials.")
  if (!decoded.hasOwnProperty("email") || !decoded.hasOwnProperty("expirationDate")) {
    res.send("Invalid auth credentials.")
  const { expirationDate } = decoded
  if (expirationDate < new Date()) {
    res.send("Token has expired.")
  res.send("User has been validated.")

This authentication check gets the user's token from the URL query and tries to decode it with the secret that was used to create it. If that fails, it returns an error message to the front-end. If the token is successfully decoded, a few more checks occur and then the user is authenticated and has access to the app!

Best practices for existing authentication systems

Passwordless authentication might not be possible for existing systems, but there are things you can do to make your apps more secure.

  • Increase the complexity requirements of passwords.
  • Use two-factor authentication.
  • Require passwords to be changed after a certain amount of time.


There are a lot of different ways you can implement an authentication system for your app and passwordless is just one of those. Token-based is another commonly used type of authentication and there are plenty of ways to handle this.

Making your own authentication system might take more work than you have time for. There are a lot of existing libraries and services that you can use to integrate authentication in your app. Some of the most commonly used ones are Passport.js and Auth0.

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