PasswordBroker without User class

I have a project where I am using Laravel to manage Stripe and to send e-mails. All my users (and authentication service) are stored in another server. As Laravel is the responsible for sending e-mails, I want to create a reset password and I am trying to implement Password Broker without having an User class, but no success until now.

I can implement a system to reset user's password manually but I'd like to take the advantage and user Laravel's password system.

So, Is it possible to do this?