custom PHP Script for Drupal conditional actions

I have a store that sells software via drupal + ubercart marketplace. I have different vendors, but some of them require to run custom PHP code after each transaction related to their products. Sample code of the script, that needs to be implemented, is already written and has been provided by the vendor. What it does: It creates a hash of such drupal's tokens as a customer name, product name, an email and a country + secret key. What has to be done: 1. We need to translate that script into drupal environment, via conditional actions or any other way. 2. Our Drupal should issue a POST(recommended) or GET request to the vendor's script and send all that HASH information in there. We have a lot of vendors and transactions, but this procedure has to be implemented only IF transaction is related to that specific vendor.