Form validation by my own method

Hello all!

I have a very simple task, but I can't make this :-( I have to check login and password in the database. So I have simple web form with two fields: login and password. I have a controller with rules:

PHP Code:

$rules = array(
    array(
    "field" => "login",
    "label" => "Username",
    "rules" => array("trim", "required", array("is_accessable", array($this->users, "get_access"))),
    ),
    array(
    "field" => "password",
    "label" => "Password",
    "rules" => "trim|required",
    ),
);
$this->form_validation->set_message("is_accessable", "Wrong login and password."); 


And I have the model Users with the method get_access. But this method takes two parameters (login, password).

The question is, how can I pass second parameter to method get_access()?

Thank you very much in advance!

P.S.: Sorry for my English.