How do I authenticate a WebClient request?

I am making a call to a page on my site using webclient. I’m trying to get the result of the webpage put into a pdf so I am trying to get a string representation of the rendered page. The problem is that the request is not authenticated so all I get is a login screen. I have sent the UseDefaultCredentials property to true but I still get the same result. Below is a portion of my code:

Limit WebClient DownloadFile maximum file size

In my asp .net project, my main page receives URL as a parameter I need to download internally and then process it. I know that I can use WebClient’s DownloadFile method however I want to avoid malicious user from giving a url to a huge file, which will unnecessary traffic from my server. In order to avoid this, I’m looking for a solution to set maximum file size that DownloadFile will download.