How develop Model and validation

I think bettet create service class for handling logic process. You can use multiple model (example save log history), and also if you want to create REST Api login, you just call this service class. You can prevent duplicating code for login. Read ADR pattern.

Hope this help

I would also second that because if I were you, I would do that because then service class would make my work easier.Also, it is easier to prevent duplication of login code.

But then again, it really depends on you.