Javascript

WebAuthn requires JavaScript to interact with authenticators in the browser. This page explains the client-side implementation using the WebAuthn Browser API and recommended libraries.

Browser API Overview

The WebAuthn specification provides two main JavaScript APIs:

1. navigator.credentials.create() - Register a new authenticator (attestation)

2. navigator.credentials.get() - Authenticate with a registered authenticator (assertion)

Both APIs are asynchronous and return Promises that resolve with credential objects.

HTTPS Requirement

HTTPS is mandatory for WebAuthn to work. This applies to all domains, including localhost. The only exception is localhost in some browsers during development, but production environments must always use HTTPS.

Modern browsers enforce this requirement to prevent credential theft and man-in-the-middle attacks.

Recommended Libraries

@simplewebauthn/browser

We highly recommend using @simplewebauthn/browser. This library:

• Simplifies the WebAuthn API with easy-to-use functions

• Handles base64url encoding/decoding automatically

• Provides TypeScript type definitions

• Is fully compliant with the WebAuthn specification

• Works with any server implementation

Installation:

Symfony UX Stimulus Controller

If you're using Symfony, the Stimulus Controller provides seamless integration with forms and authentication workflows without writing JavaScript code.

Registration (Attestation) Flow

Using Native Browser API

// 1. Fetch registration options from your server
const optionsResponse = await fetch('/webauthn/register/options', {
    method: 'POST',
    headers: { 'Content-Type': 'application/json' },
    body: JSON.stringify({
        username: '[email protected]',
        displayName: 'John Doe'
    })
});

const options = await optionsResponse.json();

// 2. Convert base64url strings to ArrayBuffers
const publicKeyCredentialCreationOptions = {
    ...options,
    challenge: base64urlDecode(options.challenge),
    user: {
        ...options.user,
        id: base64urlDecode(options.user.id)
    },
    excludeCredentials: options.excludeCredentials?.map(cred => ({
        ...cred,
        id: base64urlDecode(cred.id)
    }))
};

// 3. Call the WebAuthn API
const credential = await navigator.credentials.create({
    publicKey: publicKeyCredentialCreationOptions
});

// 4. Encode response for server
const attestationResponse = {
    id: credential.id,
    rawId: base64urlEncode(credential.rawId),
    type: credential.type,
    response: {
        clientDataJSON: base64urlEncode(credential.response.clientDataJSON),
        attestationObject: base64urlEncode(credential.response.attestationObject)
    }
};

// 5. Send to server for validation
await fetch('/webauthn/register', {
    method: 'POST',
    headers: { 'Content-Type': 'application/json' },
    body: JSON.stringify(attestationResponse)
});

Using @simplewebauthn/browser

import { startRegistration } from '@simplewebauthn/browser';

try {
    // 1. Fetch registration options from your server
    const optionsResponse = await fetch('/webauthn/register/options', {
        method: 'POST',
        headers: { 'Content-Type': 'application/json' },
        body: JSON.stringify({
            username: '[email protected]',
            displayName: 'John Doe'
        })
    });

    const options = await optionsResponse.json();

    // 2. Start registration (handles encoding automatically)
    const attestationResponse = await startRegistration(options);

    // 3. Send to server for validation
    const verificationResponse = await fetch('/webauthn/register', {
        method: 'POST',
        headers: { 'Content-Type': 'application/json' },
        body: JSON.stringify(attestationResponse)
    });

    const verificationResult = await verificationResponse.json();

    if (verificationResult.verified) {
        alert('Registration successful!');
    }
} catch (error) {
    console.error('Registration failed:', error);
    alert('Registration failed: ' + error.message);
}

Authentication (Assertion) Flow

Using Native Browser API

// 1. Fetch authentication options from server
const optionsResponse = await fetch('/webauthn/login/options', {
    method: 'POST',
    headers: { 'Content-Type': 'application/json' },
    body: JSON.stringify({
        username: '[email protected]'
    })
});

const options = await optionsResponse.json();

// 2. Convert base64url strings to ArrayBuffers
const publicKeyCredentialRequestOptions = {
    ...options,
    challenge: base64urlDecode(options.challenge),
    allowCredentials: options.allowCredentials?.map(cred => ({
        ...cred,
        id: base64urlDecode(cred.id)
    }))
};

// 3. Call the WebAuthn API
const credential = await navigator.credentials.get({
    publicKey: publicKeyCredentialRequestOptions
});

// 4. Encode response for server
const assertionResponse = {
    id: credential.id,
    rawId: base64urlEncode(credential.rawId),
    type: credential.type,
    response: {
        clientDataJSON: base64urlEncode(credential.response.clientDataJSON),
        authenticatorData: base64urlEncode(credential.response.authenticatorData),
        signature: base64urlEncode(credential.response.signature),
        userHandle: credential.response.userHandle
            ? base64urlEncode(credential.response.userHandle)
            : null
    }
};

// 5. Send to server for validation
await fetch('/webauthn/login', {
    method: 'POST',
    headers: { 'Content-Type': 'application/json' },
    body: JSON.stringify(assertionResponse)
});

Using @simplewebauthn/browser

import { startAuthentication } from '@simplewebauthn/browser';

try {
    // 1. Fetch authentication options from server
    const optionsResponse = await fetch('/webauthn/login/options', {
        method: 'POST',
        headers: { 'Content-Type': 'application/json' },
        body: JSON.stringify({
            username: '[email protected]'
        })
    });

    const options = await optionsResponse.json();

    // 2. Start authentication (handles encoding automatically)
    const assertionResponse = await startAuthentication(options);

    // 3. Send to server for validation
    const verificationResponse = await fetch('/webauthn/login', {
        method: 'POST',
        headers: { 'Content-Type': 'application/json' },
        body: JSON.stringify(assertionResponse)
    });

    const verificationResult = await verificationResponse.json();

    if (verificationResult.verified) {
        window.location.href = '/dashboard';
    }
} catch (error) {
    console.error('Authentication failed:', error);
    alert('Authentication failed: ' + error.message);
}

Base64URL Encoding/Decoding

If you're using the native API without a library, you need helper functions for base64url encoding:

function base64urlEncode(buffer) {
    const base64 = btoa(String.fromCharCode(...new Uint8Array(buffer)));
    return base64
        .replace(/\+/g, '-')
        .replace(/\//g, '_')
        .replace(/=/g, '');
}

function base64urlDecode(base64url) {
    const base64 = base64url
        .replace(/-/g, '+')
        .replace(/_/g, '/');
    const padding = '='.repeat((4 - base64.length % 4) % 4);
    const binary = atob(base64 + padding);
    const bytes = new Uint8Array(binary.length);
    for (let i = 0; i < binary.length; i++) {
        bytes[i] = binary.charCodeAt(i);
    }
    return bytes.buffer;
}

The @simplewebauthn/browser library handles all encoding/decoding automatically, which is why we recommend it.

Error Handling

WebAuthn operations can fail for various reasons. Always wrap calls in try-catch blocks:

import { startAuthentication } from '@simplewebauthn/browser';

try {
    const response = await startAuthentication(options);
    // Success
} catch (error) {
    // Handle different error types
    if (error.name === 'NotAllowedError') {
        alert('Operation cancelled or timed out');
    } else if (error.name === 'InvalidStateError') {
        alert('Authenticator already registered');
    } else if (error.name === 'NotSupportedError') {
        alert('WebAuthn not supported in this browser');
    } else if (error.name === 'AbortError') {
        alert('Operation was aborted');
    } else {
        alert('Authentication failed: ' + error.message);
    }
}

Common Error Types

Error Name	Description	Common Cause
NotAllowedError	User cancelled the operation or timeout	User cancelled prompt, 60-second timeout exceeded
InvalidStateError	Invalid state for operation	Authenticator already registered for this account
NotSupportedError	Operation not supported	Browser doesn't support WebAuthn or specific features
SecurityError	Security requirements not met	Not using HTTPS, invalid origin/RP ID
AbortError	Operation aborted	Explicitly cancelled by application code

Browser Compatibility

WebAuthn is supported in modern browsers:

• ✅ Chrome 67+

• ✅ Firefox 60+

• ✅ Safari 13+ (iOS and macOS)

• ✅ Edge 18+

• ✅ Opera 54+

Always check for WebAuthn support before attempting registration or authentication:

if (!window.PublicKeyCredential) {
    alert('WebAuthn is not supported in this browser');
    // Show fallback authentication method
    return;
}

// Optional: Check for specific features
if (window.PublicKeyCredential.isUserVerifyingPlatformAuthenticatorAvailable) {
    const available = await PublicKeyCredential.isUserVerifyingPlatformAuthenticatorAvailable();
    if (available) {
        console.log('Platform authenticator (Touch ID, Face ID, Windows Hello) available');
    }
}

Browser Autofill / Conditional UI

Modern browsers support autofill for WebAuthn credentials, allowing users to select passkeys from password autofill:

// Check if conditional UI is available
const conditionalUIAvailable = await PublicKeyCredential.isConditionalMediationAvailable();

if (conditionalUIAvailable) {
    // Add 'conditional' mediation to allow autofill
    const credential = await navigator.credentials.get({
        publicKey: options,
        mediation: 'conditional'  // Enable autofill UI
    });
}

For Symfony UX users, enable this with the useBrowserAutofill option in the Stimulus controller configuration.

Development Setup

Local HTTPS

For development with HTTPS on localhost:

Option 1: Use mkcert (Recommended)

# Install mkcert
brew install mkcert  # macOS
# or apt install mkcert  # Linux

# Create local CA
mkcert -install

# Generate certificate for localhost
mkcert localhost 127.0.0.1 ::1

Option 2: Symfony CLI (for Symfony projects)

symfony server:ca:install
symfony serve

The Symfony CLI automatically sets up HTTPS for local development.

See Also

• @simplewebauthn/browser Documentation

• Symfony UX Integration - Framework integration

• Pure PHP Server Setup - Server-side implementation

• MDN WebAuthn API - Browser API reference