Database access using windows authentication

We are updating our Applications to use single sign on and are running into a problem with database access. We are using CF11 Enterprise and SQL Server 2008 on IIS 7.5.

We have set up the ColdFusion Application Service to run under an AD service account and have created the data sources in CFAdmin leaving the username and password blank. The data sources verify and all seems good. The problem comes when running a query. The credential passed to the database is the service account and not the windows authenticated user. As such the query fails. What are we missing to get CF to pass the Windows Authenticated user credential instead of the service account?

Thanks

Tim