Configure WebAuthn with Security Keys for MFA
Enable WebAuthn with Security Keys by going to Dashboard > Security > Multifactor Auth.
Configure how you want to handle User Verification. For security keys, the typical user verification prompts users to enter a PIN to complete the WebAuthn challenge.
Never: Users will never be prompted to enter a PIN. This is the default value, and it's usually good enough when using security keys for MFA. Users already entered their password, so already provided some verification.
If supported: Users will be prompted to enter a PIN if they already configured one in the key.
Required: Users will be asked to set a PIN if it's not already set, and they'll be asked to enter it each time. This is the option that offers the highest security. Some browsers don't implement this properly (for example, Brave on iOS) so the authentication will fail and Auth0 will ask users to use another browser.
Note that only FIDO-2 compliant security keys support user verification. FIDO-1 keys can be used for WebAuthn, but are not usable if you set User Verification to Required.
Configure Relying Party
WebAuthn makes phishing impossible by binding the credentials with the browser's origin. Users can't use WebAuthn for a site they did not register too.
Binding credentials to the origin means if you configure a custom domain or change it, users enrolled before the change will not be able to authenticate.
WebAuthn defines a Relying Party ID attribute, which lets you specify the domain used to authenticate users. You can set it to any registrable domain suffix of the browser origin. For example, if the custom domain is accounts.acme.com, you can configure the Relying Party ID to acme.com. This lets users authenticate to any acme.com domain with their WebAuthn credentials.
Auth0 lets you specify the Relying Party ID only if you have a custom domain configured. If the custom domain changes, you must update the Relying Party ID.
The latest versions of popular browsers and operating systems provide support for WebAuthn with Security Keys. For more details, check the the browser support section in webauthn.me.
When using the MFA API you can list and remove WebAuthn enrollments, but you cannot enroll them.