Is there any way to get Logged on Password using ASP.Net?

Hi,
Is there any way to get Logged on Password using ASP.Net?
Here is my requirement: I need to pass Username and Password of Logged on user to WCF service from ASP.Net page (calling wcf service from xxx.aspx page). Inside WCF service, I am creating a dynamic proxy for one web service(.asmx). while creating proxy i need to use this Username and Password for authentication.
I tried to get Password from Active Directory of particular domain for particular Username, but no luck. Getting all details except the Password.
I am struggling to find, please help me on this issue. 
Regards,
Raghuveer Reddy P
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