public function authenticate()
 {
     $user = new User();
     if ($user->authenticate($this->username, $this->password)) {
         $this->_id = $user->userID;
         $this->setState('employeeID', $user->getEmployeeID());
         $this->setState('fullName', $user->getFullName());
         $this->errorCode = self::ERROR_NONE;
     } else {
         $this->errorCode = self::ERROR_UNKNOWN_IDENTITY;
     }
     return $this->errorCode == self::ERROR_NONE;
 }