you are correct about the credetials being dropped. The reason is that the server is making the request and not the client and the client is what has the credentials. A couple suggestions are
1. Add the credentials to the request by adding
objRequest.Credentials = CredentialCache.DefaultCredentials
which will pass the current credentials of the client to the request.
or
us this method to capture the output of the page http://west-wind.com/weblog/posts/481.aspx by overriding the render of the page.
Please repost if you need more information. If this solves your problem please mark as an answer to close the post.