WebClient accessing page with credentials

I suspect that the web page that you are trying to access uses Forms Authentication. This means that you will have to provide a valid authentication cookie if you want to be able to access protected resources. And in order to obtain a valid authentication cookie you will have to first authenticate yourself by sending a POST request to the LogOn page which emits the cookie. Once you retrieve the cookie you will be able to send it along on subsequent requests on protected resources. You should also note that out of the box WebClient doesn't support cookies. For this reason you could write a custom cookie aware web client:

public class CookieAwareWebClient : WebClient{    public CookieAwareWebClient()    {        CookieContainer = new CookieContainer();    }    public CookieContainer CookieContainer { get; private set; }    protected override WebRequest GetWebRequest(Uri address)    {        var request = (HttpWebRequest)base.GetWebRequest(address);        request.CookieContainer = CookieContainer;        return request;    }}

Now you could use this client to fire off the 2 requests:

using (var client = new CookieAwareWebClient()){    var values = new NameValueCollection    {        { "username", "john" },        { "password", "secret" },    };    client.UploadValues("http://domain.loc/logon.aspx", values);    // If the previous call succeeded we now have a valid authentication cookie    // so we could download the protected page    string result = client.DownloadString("http://domain.loc/testpage.aspx");}

Obviously due to the ViewState crapiness of ASP.NET you might need to send a couple of other parameters along your logon request. Here's what you could do: authenticate in a web browser and look with FireBug the exact parameters and headers that need to be sent.