Choosing a Reporting Services parameter value based on the currently logged in user

Here's my situation. I have a Microsoft Reporting Services report that as a parameter takes a salesperson's name and shows them their sales across their territories blah blah blah.

But, salesperson A should not be able to choose and view salesperson B's data. So, my thought was to get the currently logged in user from Reporting Services, and then use that to populate the "salesperson" parameter.

Is there a way to get the currently logged in开发者_如何学编程 user through some hidden RS interface, or is there some other way of accomplishing my goal that I'm just not seeing? Any help would be GREAT, as the higher ups aren't too happen with my (apparent) lack of security right now.

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you can use from this in the Expression list: in SSRS 2008 : Built in Fields -> UserID