use CGI::Session;
use HTML::Template::Compiled;

sub check_login {
  my $user = shift;
  my $pw = shift;
  
  # Teste ob login gültig und gib true zurück
  return 1 
    if ($user eq 'test' and $pw eq 'gehweg123geheim'); # oder sonstige Methode zum Test der Logindaten
  
  # sonst kein gültiges Login
  return;
}

my $htc;
my $session = new CGI::Session;

my $loggedin = $session->param('LOGGEDIN') == 1;
if (not $loggedin) {
  $loggedin = check_login($session->param('username'), $session->param('password'));
  $session->param('LOGGEDIN' => $loggedin); # Login in Session sichern
}

$htc = HTML::Template::Compiled->new(
  filename => '/var/www/vhosts/example.org/httpdocs/index.html'
);
$htc->param( 
  username => $session->param('username'),
  password => $session->param('password'),
  loggedin => $loggedin
);

print $session->header, $htc->output;

1;