How to manage licence keys within custom visual

[emmasaunders]

Hello,

I understand that for a custom visual to be certified within the marketplace, the code should not access external websites or databases. How, then, do I structure In-App purchases? I imagine I need to maintain a database of licence keys, and validate them from within the graphic's code when the user unlocks additional features. Is that right or is there a Microsoft-managed process? 

Thanks

Emma