Hey Arie,
I need more information about what you're trying to accomplish. If you're trying to generate product key after a purchase, then we already have a bunch of examples showing how to do it: http://wyday.com/limelm/help/how-to-generate-product-keys-after-order/
If you're trying to manage product keys, then, honestly, the best option is to use our LimeLM interface. Of course, you could always use the web API to replicate what we already offer inside the LimeLM interface.