This add-on is marked as unmaintained. I may update it at a later date, but I might not.
This addon allows you to verify the XenForo licenses of your members.
There is a nice front-end UI that allows a user to enter their API token and domain.
The admin can set these options:
The API key will be saved to the database if the option is enabled (it is by default), and you can require a unique API key to be provided (will only work if API's are saved).
You can also require the domain to be the domain for the API key.
Finally, the addon will also check licenses every X days, and if they're no longer valid then the user will be removed from the usergroup.