AbleCommerce Shopping Cart Software

I need some way to manage users and license keys for digital goods via a web service. I have a custom cd key generation system in place that has a webservice and usernames. I need to push sync these two systems when items change. I also need to add keys to the digital good based on the digital good name and if there are less than 10 keys left in the list.

Is this possible?

Yes its doable. If you want to keep two system in sync then one possibility might be to write your custom licensing provider. Read following thread
http://wiki.ablecommerce.com/index.php/ ... ing_Module

If you look at AcquireSerialKey() method in licensing module you will see here we are handling the serial keys from Database. In your case you can implement this method for your custom provider in a way where it will grab serial key from web service and will return it in response.

What about for user syncronization across multiple systems?