Add authentication to any web page

Learn how to add authentication to any web page without using Authgear's SDKs with IIFE(Immediately-invoked Function Expression) bundle

In this guide, you'll make a simple website server to host the SPA app using ExpressJS. We'll also use it to serve our HTML page and any assets it needs, like JavaScript, CSS, and so on. You can also view a full-source code on the GitHub repo.


  • Before we start, ensure you have Node.js installed in your system. If not, download and install it from the official website.

  • An Authgear account: You need an Authgear account to follow this guide. If you don't have one, you can create it for free on the Authgear website.

  • A Registered App: You need a registered application type (Single Page Application) in Authgear. Follow the setup application guide and skip installing the Authgear Web SDK part. You will retrieve the Authgear Web SDK from Authgear's CDN using IIFE(Immediately-invoked Function Expression) bundle and reference a script in our HTML directly.

Create a basic web server

Start with making a new folder on your computer to keep the app’s source code (In the example, we call it authgear-spa-js-login). Then, initialize a new NPM project by running the following command:

npm init -y

Next, we install two required packages:

npm install express

Also, install nodemon so that our server can be restarted automatically on any code changes in dev mode:

npm install -D nodemon

Next, open the package.json file and edit scripts entry to have start and dev commands like the below:

  // ...
  "scripts": {
    "start": "node server.js",
    "dev": "nodemon server.js"
  // ...

Now you can run the app in two modes: prod and dev.

For example, npm run dev will run the application using nodemon, monitoring for changes as we modify files.

Creating server.js

Create a new file server.js in the root of the project and populate it with the following code:

const express = require("express");
const { join } = require("path");
const app = express();

// Serve static assets from the /public folder
app.use(express.static(join(__dirname, "public")));

// Endpoint to serve the configuration file
app.get("/authgear_config.json", (req, res) => {
  res.sendFile(join(__dirname, "authgear_config.json"));

// Serve the index page for all other requests
app.get("/*", (_, res) => {
  res.sendFile(join(__dirname, "index.html"));

// Listen on port 3000
app.listen(3000, () => console.log("Application running on port 3000"));

Create a basic HTML page

Create a index.html file in the root of the project and add the following content to the created file:

<!DOCTYPE html>
    <meta charset="UTF-8" />
    <title>Authgear SPA SDK Sample</title>
    <link rel="stylesheet" type="text/css" href="/css/main.css" />

    <h2>SPA Authentication Sample</h2>
    <p>Welcome to our page!</p>
    <button id="btn-login" disabled="true" onclick="login()">Log in</button>
    <button id="btn-logout" disabled="true" onclick="logout()">Log out</button>
    <script src="js/app.js"></script>
    <script src="<>"></script>

We do not use a package manager such as Webpack, we will retrieve the Authgear Web SDK from Authgear's CDN using IIFE(Immediately-invoked Function Expression) bundle. We can reference a script in our HTML directly:

<script src="<>"></script>

You can install the Authgear Web SDK as a dependency of your application, it is useful if you are building React or React Native apps. See how to install the package.

Create a main.css file

Create a new folder called public folder in the project root folder and create another folder called css inside the public folder. Add a new file in there called main.css. This will be used to determine how the log-in and log-out button elements will be hidden on the main page depending on whether a user is authenticated or not.

Open the newly-created public/css/main.css file and add the following CSS:

.hidden {
    display: none;
label {
    margin-bottom: 10px;
    display: block;

After creating an HTML file and applying CSS styles, see now how our page looks like by running npm run dev and accessing it at http://localhost:3000.

Create an app.js file

To add some action to the page, we create a new directory in the public folder called js, and add a new file there called app.js. Copy and paste the following JS code that reads authgear_config.json file Authgear app-specific values (endpoint and clientId) from the endpoint using fetchAuthConfig function. Also, it configures a new Authgear client, and defines login and logout logic:

let authgearClient = null;

const fetchAuthConfig = () => fetch("/authgear_config.json");

const configureClient = async () => {
    const response = await fetchAuthConfig();
    const config = await response.json();
    authgearClient = window.authgear.default;

    await authgearClient.configure({
        endpoint: config.endpoint,
        clientID: config.clientID,
        sessionType: "refresh_token",
        () => {
            console.log("Authgear client successfully configured!");
        (err) => {
            console.log("Failed to configure Authgear");

const login = async () => {
    await authgearClient
            redirectURI: window.location.origin,
            prompt: "login",
            () => {
                console.log("Logged in!");
            (err) => {
                console.log("Log in failed", err);

const logout = () => {
      redirectURI: window.location.origin,
      () => {
        console.log("Logged out successfully");
      (err) => {
        console.log("Failed to logout");

window.onload = async () => {
    await configureClient();

    const query =;
    if (query.includes("code=")) {


        window.history.replaceState({}, document.title, "/");

const updateUI = async () => {
    const isAuthenticated = authgearClient.sessionState === "AUTHENTICATED";

    document.getElementById("btn-logout").disabled = !isAuthenticated;
    document.getElementById("btn-login").disabled = isAuthenticated;

Understanding the whole picture

Let’s breakdown down app.js code in the previous section and understand how authentication is achieved with Authgear:

Configure the Authgear client

fetchAuthConfig: Firstly, this function makes a request to the /authgear_config.json the endpoint we exposed in server.js to fetch Authgear app setting values from authgear_config.jsonfile.

configureClient: Once we retrieve the configuration information for the Authgear client from the authgear_config.json file and we set up the Authgear client with these settings. It also logs a message to the console, informing whether the configuration was successful or not.

Login flow

login: The function is called by the Login button previously defined on the HTML page. It performs the login action by calling authgearClient.startAuthentication Authgear’s function. It redirects the user to the Auhthgear login page. After the user logs in successfully, they will be redirected back to the same page we set in redirectURI. Run the project and click the Login button. You should be taken to the Authgear Login Page configured for your application.

Go ahead and create a new user or log in using an email (we specified the Passwordless Email login method in the first part). When you try to log in with your email, you should receive a magic link to your email box to confirm login operation.

After authenticating successfully, you will be redirected to the page you were before.

Logout flow

logout: This function logs the user out and redirects them back to the original page (athttp://localhost:3000). It uses Authgear’s logout function and logs a message to the console indicating the result of the operation.

Update the UI

window.onload: This is a function that runs when the page loads. It configures the Authgear client and updates the UI. If the page's URL contains a "code=" it means the user is authenticated (code the query will be received from the Authgear server), it updates the UI again and removes the "code=" from the URL.

Evaluate the authentication state

updateUI: This function updates the status of the login and logout buttons based on whether the user is authenticated or not. In Authgear, you can check if the user has logged in or not with sessionState the attribute. If the user is authenticated, we disable the login button and enable the logout button, and vice versa if the user is not authenticated.

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