Hi,
You can do it by many ways:
1) Javascript Querystring:
On click of a button in child window just use this:
this.Page.ClientScript.RegisterStartupScript(GetType(), "dd1", "<script language='javascript'>window.opener.location.href=http://localhost:9880/testProject/Home.aspx?username='"+UserName+"'&Pass='"+Pass+"'; self.close();</script>");
But this will not be a good practice.
2)Session:
If you really want to send the username and password then send it through session.
Follow the link for using session variable:
Manage ASP.NET Session Variables using the Facade Design Pattern[
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http://msdn.microsoft.com/en-us/library/ms178581.aspx[
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All the best.
--AK