How to impersonate by token taken from windows authentication?

I have web application with windows authentication(WinApp)
and another web application with Forms authentication(FormsApp).
In WinApp I get the current user token from current WindowsIdentity object
Then I pass that token  to FormsApp where I impersonate by this token.
FormsApp is working well but access to sql server  is anonymous.
Web server and Sql server are on separate machines.
How should I get a token from WinApp to be able to access network resources after impersonation in FormsApp?
I read an article that I should use DuplicateTokenEx method(advapi32.dll method)
to get a primary token for that user.
But I do not know how. 
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