[support] Create api for interface with an application

Hi all. I need to create a simil-gateway from Drupal to application X and from application X to Drupal. In other words I have an application (an ecommerce) and I want to interact in double-way (Drupal to ecomm and ecomm to Drupal) with it. For example: ecommerce's users are the drupal'user so I need to write an api (called from ecommerce) that get the user information, make login, make logout, etc etc.

I have tried to create and call (via browser, after a login in Drupal) a file like this:

<?php

include_once './includes/bootstrap.inc'; drupal_bootstrap(DRUPAL_BOOTSTRAP_FULL);

print_r($user);

?>

but the result is that the "uid" is 0. Why ?

Does anyone can give me some type of RTFM ?

M.