Some (untested) code...

Set the cookie containing the username and an encrypted key (the password + $key):

use Crypt::CBC;

my $key = 'kjhAG43asoiudy3kjq43ajhali87LOljkYilKH84yiHLkjklasjsd98fu';

my $cipher = new Crypt::CBC($key,'Blowfish');
my $crypt = $cipher->encrypt($password);

$cgi = new CGI;

my $auth = "$user,$crypt";

$cookie = $cgi->cookie (
    -name    => 'hostauth',
    -value   => $auth
);

print $cgi->header (-type => 'text/html', -cookie => $cookie);
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And then, whenever you want, you can decrypt the key in the cookie (using the same $key) and send it along to the LDAP server:

use Crypt::CBC;

my $key = 'kjhAG43asoiudy3kjq43ajhali87LOljkYilKH84yiHLkjklasjsd98fu';

my $cipher = new Crypt::CBC($key,'Blowfish');
my $auth = $cipher->decrypt($cookie);

# Send the $auth to the LDAP server...
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-s.