Passing Session variables to extenal scripts

Hi.

Ive been trying everything to pass session variables to external php scripts from my drupal pages.
I am adding custom user data to the database which is generated within a form by the user in a drupal page.

I am using external php to add the data to the database however it requires the user id or UID

i can use querystrings for example addDetails.php?uid=9 however for security reasons i dont want to do this

I have spent hours on your forum and all i can find are people ranting on and no proper solution, this is something that should be relatively simple.

I literally just want to access a simple $_SESSION['uid'] variable , how hard can it be??

Any help would be much appreciated

Thanks