wordpress session and cookie handling

Paste this code into your functions.php file for sessions:

function register_my_session()
{
  if( !session_id() )
  {
    session_start()
  }
}

add_action('init', 'register_my_session');
Now if you want to use sessions its:

$_SESSION['username'] = 'landing-page';

You need to identify the $_SESSION has started already (with session_name()) to check if:

a) there's a session there already and then
b) if that session is your own
and act accordingly; in this case, destroy their session and then set your own with its own parameters