prompt network people but not outside people

Hi, I have a question.aspx page that allows "guests" and "admin" to use. If guest access the page, it says Submit, if admin access it, it says "Approve" on the button control.


My question is, when guest accesses that page, I don't care about their credentials, but when admin accesses that page, I want them to log in first. And the Admin users are the ones that work in our company with the same domain and such. Anyone that access outside would be "guest".. how can I prompt people in the same network when they try to access that page? I need that AD credentials to do some programming in code behind.

Thanks!
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