# build POST request
my $req = HTTP::Request->new('POST', $postURL);  # $postURL is "http://everything2.org/index.pl"
$req->content_type('application/x-www-form-urlencoded');
$req->content($postData);  # $postData is "op=login&username=FOO&password=BAR" or somesuch

# get the page
my $response = $ua->request($req);

if ($response->is_success) {
    # extract the cookie from the response and return the HTTP::Cookies object
    $loginCookieJar->extract_cookies($response);
    $loginCookieJar;
} else {
    die "Could not log in.\n";
}