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interessante articolo (in inglese) spiega come utilizzare il meccanismo dell'impersonificazione con .Net
Impersonation is one of the most useful mechanisms in Windows security. It's also fragile and easy to misuse. Careful use of impersonation can lead to a secure, easy-to-administer application. Misuse can open gaping security holes. This sample chapter will help you to use impersonation properly and effectively.