אם השם משתמש והסיסמא טובים - לפי דרך בדיקה שלך, אז ככה:
 
$_SESSION['con']="ok";

//check if username and passwords are correct
else {
    //first users group
    if (
            $user == $username[1] && $pass == $password[1] ||
            $user == $username[2] && $pass == $password[2] ||
            $user == $username[3] && $pass == $password[3] ||
            $user == $username[4] && $pass == $password[4] ||
            $user == $username[5] && $pass == $password[5]
        ) {
		
        $_SESSION['con']=$user;
        if ($open_type == 0) {
            include ("$file3");
        } else {
            header("Location: $url_redirect_1"); 
            exit;
        }
    }
		
    //second users group
    elseif (
            $user == $username[6] && $pass == $password[6] ||
            $user == $username[7] && $pass == $password[7] ||
            $user == $username[8] && $pass == $password[8] ||
            $user == $username[9] && $pass == $password[9] ||
            $user == $username[10] && $pass == $password[10]
        ) {
		
        $_SESSION['con']=$user;
        if ($open_type == 0) {
            include ("$file4");
        } else {
            header("Location: $url_redirect_2"); 
            exit;
        }
    }

<php?

?>