Authenticator Selection Criteria

By default, any type of authenticator can be used by your users and interact with you application. In certain circumstances, you may need to select specific authenticators e.g. when user verification is required.

The Webauthn API and this library are allow you to define a set of options to disallow the registration of authenticators that do not fulfill with the conditions.

The class Webauthn\AuthenticatorSelectionCriteria is designed for this purpose. It is used when generating the Webauthn\PublicKeyCredentialCreationOptions object.

Available Criterias

Authenticator Attachment Modality

You can indicate if the authenticator must be attached to the client (platform authenticator i.e. it is usually not removable from the client device) or must be detached (roaming authenticator).

Possible values are:

• AuthenticatorSelectionCriteria::AUTHENTICATOR_ATTACHMENT_NO_PREFERENCE: there is no requirement (default value),

• AuthenticatorSelectionCriteria::AUTHENTICATOR_ATTACHMENT_PLATFORM: the authenticator must be attached,

• AuthenticatorSelectionCriteria::AUTHENTICATOR_ATTACHMENT_CROSS_PLATFORM: must be a roaming authenticator.

A primary use case for platform authenticators is to register a particular client device as a "trusted device" for future authentication. This gives the user the convenience benefit of not needing a roaming authenticator, e.g., the user will not have to dig around in their pocket for their key fob or phone.

Resident Key

When this criteria is set to true, a Public Key Credential Source will be stored in the authenticator, client or client device. Such storage requires an authenticator capable to store such resident credential.

This criteria is needed if you want to authenticate users without username.

User Verification

User verification may be instigated through various authorization gesture modalities: a touch plus PIN code, password entry, or biometric recognition (presenting a fingerprint).The intent is to be able to distinguish individual users.

Possible values are:

• AuthenticatorSelectionCriteria::AUTHENTICATOR_ATTACHMENT_NO_PREFERENCE: the authenticator should verify the user if possible (default value),

• AuthenticatorSelectionCriteria::USER_VERIFICATION_REQUIREMENT_REQUIRED: the authenticator must verify the user,

• AuthenticatorSelectionCriteria::USER_VERIFICATION_DISCOURAGED: the authenticator must NOT try to verify the user. This option may be set in the interest of minimizing disruption to the user interaction flow.

Examples

The Easy Way

<?php

use Webauthn\AuthenticatorSelectionCriteria;
use Webauthn\PublicKeyCredentialCreationOptions;

$authenticatorSelectionCriteria = new AuthenticatorSelectionCriteria(
    AuthenticatorSelectionCriteria::AUTHENTICATOR_ATTACHMENT_PLATFORM,     // Platform authenticator
    true,                                                                  // Resident key required
    AuthenticatorSelectionCriteria::USER_VERIFICATION_REQUIREMENT_REQUIRED // User verification required
);

$publicKeyCredentialCreationOptions = $server->generatePublicKeyCredentialCreationOptions(
    $userEntity,
    PublicKeyCredentialCreationOptions::ATTESTATION_CONVEYANCE_PREFERENCE_NONE,
    $excludedPublicKeyDescriptors,
    $authenticatorSelectionCriteria
);

The Hard Way

The Symfony Way