In your AppView, load the Helper as:
$this->loadHelper('Authentication.Identity');
For very simple checking whether the user is logged in you can use:
if ($this->Identity->isLoggedIn()) {
...
}
Getting user data can be done with:
$username = $this->Identity->get('username');
The following check can be used to tell if a record that belongs to some user is the current logged in user and compare other fields as well:
$isCurrentUser = $this->Identity->is($user->id);
$isCurrentRole = $this->Identity->is($user->role_id, 'role_id');
This method is mostly a convenience method for simple cases and not intended to replace any kind of proper authorization implementation.