Register Authenticators

During this step, your application will send a challenge to the device. The device will resolve this challenge by adding information and digitally signing the data.

The application will check the response from the device and get its credential ID. This ID will be used for further authentication requests.

Creation Request

To associate a device to a user, you need to instantiate a Webauthn\PublicKeyCredentialCreationOptions object.

It will need:

Let’s see an example of the PublicKeyCredentialCreationOptions object. The following example is a possible Public Key Creation page for a dummy user "@cypher-Angel-3000".

<?php
declare(strict_types=1);
use Cose\Algorithms;
use Webauthn\AuthenticatorSelectionCriteria;
use Webauthn\PublicKeyCredentialDescriptor;
use Webauthn\PublicKeyCredentialCreationOptions;
use Webauthn\PublicKeyCredentialParameters;
use Webauthn\PublicKeyCredentialRpEntity;
use Webauthn\PublicKeyCredentialUserEntity;
// RP Entity
$rpEntity = new PublicKeyCredentialRpEntity(
'My Super Secured Application', //Name
'foo.example.com', //ID
null //Icon
);
// User Entity
$userEntity = new PublicKeyCredentialUserEntity(
'@cypher-Angel-3000', //Name
'123e4567-e89b-12d3-a456-426655440000', //ID
'Mighty Mike', //Display name
null //Icon
);
// Challenge
$challenge = random_bytes(16);
// Timeout
$timeout = 60000; // 60 seconds
// Public Key Credential Parameters
$publicKeyCredentialParametersList = [
new PublicKeyCredentialParameters('public-key', Algorithms::COSE_ALGORITHM_ES256),
new PublicKeyCredentialParameters('public-key', Algorithms::COSE_ALGORITHM_RS256),
];
// Devices to exclude
$excludedPublicKeyDescriptors = [
new PublicKeyCredentialDescriptor(PublicKeyCredentialDescriptor::CREDENTIAL_TYPE_PUBLIC_KEY, 'ABCDEFGH…'),
];
$publicKeyCredentialCreationOptions = new PublicKeyCredentialCreationOptions(
$rpEntity,
$userEntity,
$challenge,
$publicKeyCredentialParametersList,
$timeout,
$excludedPublicKeyDescriptors,
new AuthenticatorSelectionCriteria(),
PublicKeyCredentialCreationOptions::ATTESTATION_CONVEYANCE_PREFERENCE_NONE,
null // Extensions
);

The options object can be converted into JSON and sent to the authenticator using a JS script.

It is important to store the user entity and the options object (e.g. in the session) for the next step; they will be needed to check the response from the device.

Creation Response

What you receive must be a JSON object that looks like as follow:

{
"id":"KVb8CnwDjpgAo[…]op61BTLaa0tczXvz4JrQ23usxVHA8QJZi3L9GZLsAtkcVvWObA",
"type":"public-key",
"rawId":"KVb8CnwDjpgAo[…]rQ23usxVHA8QJZi3L9GZLsAtkcVvWObA==",
"response":{
"clientDataJSON":"eyJjaGFsbGVuZ2UiOiJQbk1hVjBVTS[…]1iUkdHLUc4Y3BDSdGUifQ==",
"attestationObject":"o2NmbXRmcGFja2VkZ2F0dFN0bXSj[…]YcGhf"
}
}

There are two steps to perform with this object:

  • Load the data

  • Verify it with the creation options set above

Data Loading

Now that all components are set, we can load the data we receive using the Public Key Credential Loader service (variable $publicKeyCredential).

<?php
declare(strict_types=1);
$data = '
{
"id":"KVb8CnwDjpgAo[…]op61BTLaa0tczXvz4JrQ23usxVHA8QJZi3L9GZLsAtkcVvWObA",
"type":"public-key",
"rawId":"KVb8CnwDjpgAo[…]rQ23usxVHA8QJZi3L9GZLsAtkcVvWObA==",
"response":{
"clientDataJSON":"eyJjaGFsbGVuZ2UiOiJQbk1hVjBVTS[…]1iUkdHLUc4Y3BDSdGUifQ==",
"attestationObject":"o2NmbXRmcGFja2VkZ2F0dFN0bXSj[…]YcGhf"
}
}';
$publicKeyCredential = $publicKeyCredentialLoader->load($data);

If no exception is thrown, you can go to the next step: the verification.

Response Verification

Now we have a fully loaded Public Key Credential object, but we need now to make sure that:

  1. The authenticator response is of type AuthenticatorAttestationResponse

  2. This response is valid.

The first is easy to perform:

<?php
declare(strict_types=1);
use Webauthn\AuthenticatorAttestationResponse;
$authenticatorAttestationResponse = $publicKeyCredential->getResponse();
if (!$authenticatorAttestationResponse instanceof AuthenticatorAttestationResponse) {
//e.g. process here with a redirection to the public key creation page.
}

The second step is the verification against

  • The Public Key Creation Options we created earlier,

  • The HTTP request

The Authenticator Attestation Response Validator service (variable $authenticatorAttestationResponseValidator) will check everything for you: challenge, origin, attestation statement and much more.

The library needs PSR-7 requests. In the example below, we use nyholm/psr7-server to get that request.

<?php
declare(strict_types=1);
use Nyholm\Psr7\Factory\Psr17Factory;
use Nyholm\Psr7Server\ServerRequestCreator;
$psr17Factory = new Psr17Factory();
$creator = new ServerRequestCreator(
$psr17Factory, // ServerRequestFactory
$psr17Factory, // UriFactory
$psr17Factory, // UploadedFileFactory
$psr17Factory // StreamFactory
);
$serverRequest = $creator->fromGlobals();
$publicKeyCredentialSource = $authenticatorAttestationResponseValidator->check(
$authenticatorAttestationResponse,
$publicKeyCredentialCreationOptions,
$serverRequest
);

If no exception is thrown, the response is valid. You can store the Public Key Credential Source ($publicKeyCredentialSource) and associate it to the user entity.

The way you store and associate these objects to the user is out of scope of this library. However, please note that these objects implement \JsonSerializable and have a static method createFromJson(string $json). This will allow you to serialize the objects into JSON and easily go back to an object.

If you have just registered a new user, don’t forget to store it in your database as well.