You can try with this old article from Microsoft, it describe a way to use the Windows API, for impersonation purpose, in ASP.NET, don't be afraid about the spaghetti code you will see, just implement your call inside the:
public void Page_Load(Object s, EventArgs e)
{
if(impersonateValidUser("username", "domain", "password"))
{
//Insert your code that runs under the security context of a specific user here.
undoImpersonation();
}
else
{
//Your impersonation failed. Therefore, include a fail-safe mechanism here.
}
}