Track license code for releases and Customers

We sell our software and we need to pair our license codes with each customer we have, for each release.

We have organized ALM Complete with the right appliction/releses tree, and folders (in defects and requirements...) are based on Customer.

Which could be the best way to introduce "license code" handling?

Usage of "requirements" or "notes" in a defect card are not the right logical way, we suppose.



Have you any suggestion?