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How to: Fingerprint authentication for your webapp using javascript

How to: Fingerprint authentication for your webapp using javascript

Fingerprint and FaceID authentication powered by

Anders Åberg's photo
Anders Åberg
·Sep 5, 2021·

3 min read

In this blog post we will add Fingerprint and FaceID authentication using javascript and the passwordless API free tier to a html page using vanilla javascript. No frameworks are necessary, although the solution works great with React, Vue or Svelte (even jQuery!)

You can checkout all the code on the passwordless blog repo.

An online demo of the final result is available here: Passwordless demo

Windows hello

Create and serve index.html

You might have an existing web app that you can use, but we will create a small tutorial app. The important thing is that you can access it using either https or http://localhost:xx. (file://-protocol won't work because of security limitations)

Create a folder and open your favorite editor (mine is VS Code)

mkdir passwordless-app
cd passwordless-app
code . #open the folder in VS Code

Create a index.html file with the following code. The important part is the input, buttons and script-tags.

<!DOCTYPE html>
<html lang="en">

  <meta charset="UTF-8" />
  <meta http-equiv="X-UA-Compatible" content="IE=edge" />
  <meta name="viewport" content="width=device-width, initial-scale=1.0" />
  <title>Passwordless Minimal</title>
    body {
      font-family: sans-serif;

  <h2>Passwordless Minimal demo</h2>
  <p>To run this example you don't have to do anything other than supply a unique alias.</p>

  <input type="text" id="alias" placeholder="Unique Username, email" />
  <button id="passwordless-register">Register</button>
  <button id="passwordless-signin">Login</button>
  <pre id="status"></pre>
  <script src="" crossorigin="anonymous"></script>
  <script src="auth.js"></script>


Make sure that you include the script tags that reference the passwordless.iife.js-library and the auth.js file. Serve the file over http, e.g. using npx http-server and look at the result at http://localhost:8080.



Let's create auth.js

Add a new file called auth.js. In this file we will add our authentication code.

Start by adding the apiKey and two methods, register and sign in. (Yes, you should use the demobackend API key for this tutorial.)

 // Passwordless integration
  const apiKey = "demobackend:public:c203e65b581443778ea4823b3ef0d6af";
  const backendUrl = "";

  const p = new Passwordless.Client({ apiKey });

  async function register(alias) {
    const myToken = await fetch(backendUrl + "/create-token?alias=" + alias).then((r) => r.text());
    await p.register(myToken);
    console.log("Register succeded");
  async function signin(alias) {
    const token = await p.signinWithAlias(alias);
    const user = await fetch(backendUrl + "/verify-signin?token=" + token).then((r) => r.json());
    console.log("User details", user);
    return user;

So far so good, but we need to connect our buttons to the methods we created. In auth.js, add the following:

// Bind methods to UI buttons/events:

// register
    .addEventListener("click", async (e) => {
        const alias = document.getElementById("alias").value;
        await register(alias);
        uistatus("Succeded with register");

// sign in
    .addEventListener("click", async (e) => {
        uistatus("Starting authentication...");
        const alias = document.getElementById("alias").value;
        const user = await signin(alias)
        uistatus("User details: " + JSON.stringify(user, null, 2));

// Print Status messages to UI.
function uistatus(text) {
    const statusel = document.getElementById("status");
    const currentText = statusel.innerText;
    var newLine =
        "[" + new Date().toLocaleTimeString() + "]: " + text + "\n";
    statusel.innerText = newLine + currentText;
uistatus("Welcome! Please register or sign in");

Testing it

Refresh http://localhost:8080 again. Enter a unique nickname and click the register button.


Adding your own backend

Notice how we used "demo-backend" in this tutorial?

In the next part we will look how to connect this UI to your own backend using Node.js. It's about as easy as this was, around ~20 lines of code.

Make sure you checkout the documentation and for more info.

You can reach me at @andersaberg.

Credit: Photo by Joshua Reddekopp on Unsplash

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