Enable access to helpdesk only if user have special product

Add this code to site.php file:

function helpdeskEnabled(){
    $user = Am_Di::getInstance()->auth->getUser();
    if(!$user) return true; // give user chance to log in first
    foreach($user->getActiveProducts() as $p){
        $data = $p->getBillingPlanData();
        if($data['helpdesk_enabled']) return true;
    }
    return false;
}

Am_Di::getInstance()->billingPlanTable->customFields()
    ->add(new Am_CustomFieldSelect('helpdesk_enabled', "Enable access to helpdesk", '', '', array('options' => array(0=>'No', 1=>'Yes'))));

Am_Di::getInstance()->hook->add('userMenu',  function (Am_Event $event){
    $menu = $event->getMenu();
    if(!helpdeskEnabled()) $menu->removePage($menu->findOneBy('id', 'helpdesk'));
});

Am_Di::getInstance()->hook->add(Am_Event::INIT_CONTROLLER_PAGES,  function (Am_Event $event){
    $c = $event->getController();
    if(!is_a($c, 'Helpdesk_IndexController')) return;
    if(!helpdeskEnabled()) throw new Am_Exception_InputError('Access denied!');

});

By default access to helpdesk will be disabled for all users. You can enable it for selected products only(aMember CP -> Manage Products -> Edit Product -> Enable access to helpdesk)