/**
  * Get service object instance
  *
  * @param Zend_Config $config
  * @return Zend_Auth_Adapter_Interface
  */
 public function &getService(Zend_Config $config)
 {
     if (!$this->service) {
         $className = "Auth_Adapter_" . $config->class;
         switch ($config->class) {
             default:
                 $this->service = new $class();
                 break;
             case "Db":
                 try {
                     $this->service = new Zend_Auth_Adapter_DbTable(Zoo::getService('db')->getDb('slave'));
                     $this->service->setTableName('Auth_User')->setIdentityColumn('username')->setCredentialColumn('password')->setCredentialTreatment('md5(CONCAT(salt, ?)) AND status > 0');
                 } catch (Zoo_Exception_Service $e) {
                     // Revert to Basic authentication
                     $this->service = new Auth_Adapter_Basic();
                 }
         }
     }
     return $this->service;
 }