You can use the viewAny method on the policiy if you want to control if a user can have access to a resource. Docs: https://nova.laravel.com/docs/1.0/resources/authorization.html#policies.
public function viewAny(User $user)
{
return in_array('view-posts', $user->permissions);
}
There's also a laracasts video about this. https://laracasts.com/series/laravel-nova-mastery/episodes/7