use Net::LDAP;

# Information you'll need to populate somehow (form?)
my $base = 'dc=domain,dc=com';
my $user = 'testuser';
my $pass = 'p4ssw0rd';

my $ldap = Net::LDAP->new($host});

my $mesg = $ldap->search(
    base   => $base,
    filter => "uid=$user"
);

my ($dn);

# Search for the user's DN within the base/filter
my $max = $mesg->count;
for (my $i = 0; $i < $max; $i++) {
    my $entry = $mesg->entry($i);
    $dn = $entry->dn;
};

if ($dn) {
    # Bind with the DN & password if the user acct exists
    $mesg = $ldap->bind ($dn, password => $pass);

    unless ($mesg->code) {
        # Set the cookie here...
    }
}