here's some code from original sub admin_display that will help you:

# Now let's load the list of users.
open (PASS, "<$auth_pw_file") or &cgierr ("unable to open: $auth_pw_file.\nReason: $!");
if ($db_use_flock) { flock(PASS, 1); }
@lines = <PASS>;
close PASS;

# If we are inquiring, let's look for the specified user.
my (@data, $user_list, $perm, $password);

$user_list = qq~<select name="username"><option> </option>~;
LINE: foreach $line (@lines) {
$line =~ /^#/ and next LINE;
$line =~ /^\s*$/ and next LINE;
chomp $line;
@data = split (/:/, $line);

$data[0] is your userid

if you can get all the db's to use common pw file, you can even use filename $auth_pw_file as above.