An Extension Output Checker will check the extension output.
It must implement the interface Webauthn\AuthenticationExtensions\ExtensionOutputChecker and throw an exception of type Webauthn\AuthenticationExtension\ExtensionOutputError in case of error.
In the previous example, we asked for the location of the device and we expect to receive geolocation data in the extension output.
The easiest way to manage that is by using the creation and request profiles.