如何从ASP.NET Web服务代码对Active Directory进行身份验证？

I have a few websites for work that live outside of the corporate LAN -- and, therefore, out of direct-communication range of Active Directory (A/D) -- but for which I would like to be able to authenticate users against the corporate A/D servers as well as a secondary repository of users/roles***. The pseudo code for this activity is this:I have a few websites for work that live outsid