ASP.NET Get Windows User

[intractably]

You can protect your pages via something like:

if( User.Identity.Name != "DOMAIN\\username")
Response.Redirect("page.aspx?qid=" + qid);

You will also have to configure IIS to use Basic or Windows
authentication
and deny access to anonymous users on the ASPX page:

1. Start, Control Panel, Administrative Tools, Internet Information
Services
2. Right-click on your web application and select Properties.
3. On the Directory Security tab, select Edit for Anonymous access and
authentication control.
4. Disable Anonymous access and enable Basic authentication and/or
Integrated Windows authentication.

Otherwise, if you use anonymous access, User.Identity.Name will always
show up as "".