Utilizing existing cookies to allow customer to login to upload section

Hi there,
Here is a question that doesn't really fit anywhere else.
I've been running Zen cart for awhile now and have incorporated an upload section to my website.
I will be using Filechucker to allow customer to upload photos. Within Filechucker there is an option to use the site 'username' cookies to I can use existing cookies to allow customers access to the upload section. I just need to know where that cookie is stored. 'the name of the which is used to hold the cookie'

Hopefully this isn't too confusing.
Filechucker can integrate into existing login structures. Here is a snippet of how to configure.

# PREFs Section 04: User-directories.
############################################################################
# If you want per-username upload subdirectories, and you already have some
# kind of login framework in place on your site that stores usernames in
# cookies, then you can use this to automatically choose the right subdir
# based on the value in the cookie.  This means that each user will only
# be able to view and upload to his own subdirectory within your
# uploaded_files_dir.
#
$PREF{enable_userdir_from_cookie}            = 'yes';
$PREF{userdir_cookie_name}                = 'username';

Cheers,
Happyworker