Generate Passkey Registration Options

The username which uniquely identifies the user, e.g. email address. Will be inferred from an existing user identifier if not passed.

An additional identifier which will be displayed to the user to help them recognize the passkey.

The ID of the passkey challenge. Should be passed back to the complete the registration.

The options for public key credential creation, based on https://w3c.github.io/webauthn/#dictdef-publickeycredentialcreationoptionsjson.