How can I deactivate/expire a product for a user?

Assuming I have the user id and the product code, how can I deactivate that product for that user only from within my plugin? Thanks in advance.

Go into the invoice area of the users payment, change the end date of the payment.

David

Can you give me the code to do it from within the plugin? Thanks.

What plugin??

I have a custom payment plugin...based on information received from the payment processor, I sometimes need to deactivate a product for the current user.