How can I add expiry date in ASP.NET web application?

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ASP.NET

Hi,

I have developed an asp.net based web application that needs to be deployed on client's server(with no internet). My concern is how to add expiry date in my application/Software.

e.g If user purchase license for 1 year. It should expire after 1 year.

Adding date time check is useless if user modifies the date of his server/machine.

Any help will be appreciated.

Thanks for helping.

What I have tried:

1) I have tried adding date time check, but it fails when date is modified and can be easily cracked.