That's pretty easy with akelos. 

This is how I did it. (I'am new to Akelos-Framework but I think this way to implement authentication is ok? But anyway I know pretty less about Akelos-Framework It's fun to work with it :-) )

**prerequisites:**

a user-model with at least the following fields (name, password and e_mail). If you don't have one [[create a user-model]]

OK, You know all your controllers extends the ApplicationController (app/application_controller.php)?

place the following function into it
<code php>
<?php

require_once(AK_LIB_DIR.DS.'AkActionController.php');

/**
* This file is application-wide controller file. You can put all 
* application-wide controller-related methods here.
*
* Add your application-wide methods in the class below, your controllers 
* will inherit them.
* 
* @package ActionController
* @subpackage Base
*/

class ApplicationController extends AkActionController 
{
    
    private function authentication()
    {
        if (!empty($_SESSION['time'])) {
            
            if (!$_SESSION['time'] < time() - 1800)
                $_SESSION['time'];
        }
    }
    
    protected function forbiddenAction()
    {

        if (!empty($_SESSION['time'])) {
            
            if ($_SESSION['time'] < time() - 1800) {
                
                $_SESSION['name'] = '';
                $_SESSION['uid'] = '';
                $_SESSION['time'] = '';
                $this->redirectTo(array('controller' => 'home', 'action' => 'login'));
            }
        } else
            $this->redirectTo(array('controller' => 'home', 'action' => 'login'));
    }
}

?>
</code>

generate a home controller 

''script/generate controller Home''

write the following methods

<code php>
<?php

class HomeController extends ApplicationController
{
    var $layout = 'forum';
    var $models = 'User';
    
    public function __construct()
    {
        $this->beforeFilter('authentication', array('forbiddenAction'=>array('except'=>array('login', 'index', 'logout'))));
    }
    
    public function index()
    {
    }
    
    public function login()
    {
        if(!empty($this->params['login'])){
            
            $user = $this->User->find('first', array('conditions' => array('e_mail =?', $this->params['login']['e_mail'])));
            if ($user->password == $this->params['login']['password'])
            {
                $_SESSION['uid'] = $user->id;
                $_SESSION['name'] = $user->name;
                $_SESSION['time'] = time();
            }

        }
    }
    
    public function logout()
    {
        $_SESSION['uid'] = '';
        $_SESSION['name'] = '';
        $_SESSION['time'] = '';
        $this -> redirectTo(array('action' => 'index'));
    }
    
}

?>
</code>

now you can write a login/logout link into your template I use the layout (my layout called app/views/layouts/forum.tpl)
<code html>
{?session-name}
     <?php  echo  $url_helper->link_to($text_helper->translate('Logout'), array('controller' => 'home', 'action' => 'logout'))?> {session-name}
{else}
    <?php  echo  $url_helper->link_to($text_helper->translate('Login'), array('controller' => 'home', 'action' => 'login'))?>
{end}
</code>

now you're ready :-)

don't forget place in every controller your 

<code php>
    public function __construct()
    {
        $this->beforeFilter('authentication', array('forbiddenAction'=>array('except'=>array('index', 'listing', 'show'))));
    }
</code>

OK, hope this help a bit for the first steps ;-)

badPussycat