modifying reg_password for a domain

[Mark]

Hi,
sorry about all the support questions but I can't find this in the 
docs either.

I'm basically trial-and-error'ing my way through this when I can't 
find something so let me show you what I tried:

$cmd=array(
        "protocol" => "XCP",
        "action" => "modify",
        "object" => "domain",
        "cookie" => $cookie,
        "attributes" => array(
                "data" => "domain_auth_info",
                "reg_password" => "test-done"
        )
);

for attributes I also tried:

array(
        "reg_password" => "test-done"
);

I really have no idea what's supposed to be there. any advice is 
appreciated.

thanks,
- Mark