Getting Windows domain username in correct case (to match Active Directory) - windows

Question

How can I sensibly get a Windows 7 user's username, but in the case that it's stored in the Active Directory domain (such as BillyBird), not using whatever case the user happened to type it when logging in (probably billybird, but could even be something like bILlYbIRd)?
This is in Perl, but since it's interacting with the operating system, solutions in other languages may be translatable.
I've tried these and they don't work; they all return the username in the case it was typed by the user when logging in*:
getlogin
Win32::LoginName
$ENV{USERNAME}
Win32::OLE->new('WScript.Network')->UserName
Win32API::Net::UserGetInfo
I have come up with a couple of bad ways of getting the right value. I'll post those as answers and hope that somebody else has a better one. Thanks.
* At least they do some of the time. For some users it alternates each time they log in between giving the as-typed and the as-AD values, but in all cases the above methods all agree with each other and %USERNAME%.

Answer 1

This gets the right value, but involves fetching the list of all domain users over the network and iterating over them looking for a case-insensitive match, which seems excessive just for returning something about the current user:
use v5.16;
use Win32::NetAdmin qw<GetDomainController GetUsers FILTER_NORMAL_ACCOUNT>;
my $comparable_username = fc getlogin;
GetDomainController('', '', my $domain_controller);
GetUsers($domain_controller, FILTER_NORMAL_ACCOUNT, \my #all_username);
my $username;
for (#all_username)
{
if (fc eq $comparable_username)
{
$username = $_;
last;
}
}

Answer 2

Here's my thought about using wmic put into practice
use strict;
use warnings 'all';
say username();
sub username {
for ( `wmic useraccount get name` ) {
return $1 if /\A($ENV{USERNAME})\s*\z/i;
}
return;
}
Update
To prevent wmic from fetching the full user name list, you can use the LIKE operator in a WHERE cal
sub username {
my #user = `wmic UserAccount WHERE ( name LIKE '$ENV{username}' ) GET name`;
return unless $user[1] =~ /\S/;
$user[1] =~ s/\s+\z//r;
}

Answer 3

This is a possible solution; it gets the username in the right case:
use IPC::System::Simple qw<capturex>;
my $username;
foreach (capturex qw<NET USER /DOMAIN>, getlogin)
{
if (/^User name\s*(\S+)$/)
{
$username = $1;
last;
}
}
However it involves running an external system command to parse its output (which is relatively slow), and relies on that output always being in English. An alternative solution that used an API for directly looking up whatever the NET USER command is doing would be superior to this one.