Advice on which technology to use for datatransfer over the internet

My newest task is going to be to implement automatic update of a licence:

The program detects that the licence is expired or about to expire and offers the user to automatically upate this. So far s开发者_如何学JAVAo good. Now what is needed:

• The program sends the user's credentials to a win 2008 server over the internet.
• The server checks the credentials and if they are OK generates a licence file that is sent back.

How to implement these steps? I consider using WCF, with which I have some experience.

The transfer mechanism isn't the issue. WCF should work fine. You could use SSL and/or WCF Security.

The inherent security of the credentials and license is the concern. Remember, anyone can call the service and former clients have access to expired license files. People may try to cheat the system. Ask yourself questions such as:

• Can person A figure out what person B's credentials are and request a license as person B?
• Can a person reverse-engineer a license file and extend its life?

See for instance Need advice to design 'crack-proof' software (and numerous other SO posts on licensing).