Best way for check user is logged in or not

[eluser]xwero[/eluser]
The model is only the base for the authentication and authorization of the users. The model just has to have methods to fetch and manipulate the user data.

The library or a controller takes care of what will happen if a user tries to login, wants to change data, which parts and features of the site the user has access to, ...

Because it's a thing most sites need people already developed a variety of solutions for it. So instead of making the same mistakes the people who developed those solutions by coding it yourself, you can make use of their solutions and cut down on development time.