Laravel multi site/multi domain project structure

Requirements:
- laravel 5.x based
- single sign on
- shared users and some resources (files)

we have multiple sites (like 12 or so) build with some custom codeigniter framework which we would like to rebuild in laravel. The sites will share some data like user profile, resources (files, images...).

One colleague suggested that every site will be on it's own server and have it's own laravel app and their own database. Every site will have it's own user database which will be synced between all the sites.
This solution doesn't seem right to me. I think that the users should be somehow centralized. But I have no experience with designing such complex solutions so I may be wrong.

What would be the best way to design something like that?

via Chebli Mohamed