register: service will create a new account linked to user's linkingKey.
login: service will login user to an existing account linked to user's linkingKey.
link: service will link a user provided linkingKey to user's existing account (if account was not originally created using lnurl-auth).
auth: some stateless action which does not require logging in (or possibly even prior registration) will be granted.
This may be useful to distinguish for clients using js-lnurl
https://github.com/lnurl/luds/blob/luds/04.md#wallet-to-service-interaction-flow outlines an optional
action
enum:This may be useful to distinguish for clients using
js-lnurl