windows authentication issue

Some one please help me with the following scenrio

i have a Login page where user enters the username and password that should be validated or authenticated against windows authentication .Example
There are some 10 users in a network
lets say
1)sam
2)pam
3)peter
they are three users
now sam logged in his computer with username
username:sam
pwd:12345

now peter wants to open on internet web application to do some work in sam's computer now the web application should check peter's credientials in Sam's computer.how to do that using Windows authentication.

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