How can I cache credentials in a Web Service?

I have a REST web service running on a Windows 2003 Server. I want to prompt my users from a mobile app to enter their Windows domain credentials. I want to send those credentials to the web service, and cache them for a few days. It appears I can cache the credentials using the low-level Credentials Management functions but everything I've seen so far implies they're made to be called from an interactive session. What's the best way to cache these credentials in a web service?开发者_如何学JAVA

MORE INFO: The reason why I need to cache the credentials in the Web Service is because I need them to access some back-end resources (i.e. SQL Server, etc.)

You don't typically cache things in a web service.

How are you prompting them to enter their credentials to begin with? That app / piece should cache the information.

It appears that Windows Identity Foundation provides a better mechanism to accomplish what I want. I'll be looking into that.