asp.net Windows Authentication electronic approval

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ASP.NET

here is the background. I have an asp.net 3.5 site on an intranet that uses windows integrated authentication (NTLM) and the browser is IE and is set to auto authenticate with out prompt. My goal/wish is to have a button that a user clicks to "electronically approve" something by someone else that is not logged into the computer. so you have 2 users, generic user and lets say admin. the gen. user is logged into the site, calls over the admin to approve something so the admin clicks the button and it pops up the default windows authentication dialog, assuming the admin is validated the admins username and todays date and time are recored in the background (sent to sql db) once finished the gen user continues on with work and is still logged into the site as him/herself.

one thing i am aware of is the LogonUser function. the problem with that is i dont want to ever handle at all the admins user name and password. I want windows to handle it.

please tell me there is another way to do it. i have been dabling with the "sign on as different user" technique that sharepoint uses but it completely switches users. All i really need to do in the end is check to see if the person's info has been authenticated ,
if yes insert timestamp and username to db. if no do nothing. the catch is i want windows dialog for password to handle it.

any help would be greatly appreciated! thank you!