After user registration, website send activation code to email. something like that. www.domain.com/?activate=<code>

I'm creating 2 variants of activation: 1.manual 2.auto Lets say we have index.php.

1.Manual method. When someone wants to activate user manually all things are obvious:

User opens page www.domain.com/?activate

Index.php checks with following script and includes div file (which contains activation form)

   if (isset($_GET['activate'])) {
      $page='activate';
      $divfile = 'path to div.php';
    } 
    include $divfile;

Then page sends form data via ajax to activation.php file.

2.Auto method. Lets say user clicked directly to www.domain.com/?activate=<code>. What I wanna do is, to check if(!empty($_GET['activate'])), if all right ... I can't figure out how to act?! Programmatically send something like POST to activation.php or what? Please help. Thx in advance