Login - Wkhtmltopdf Log In To Web App?

Having a problem with wkhtmltopdf. I'm using it to take pdf snapshots of pages on a website that has a username/password page. When the .exe runs, I end up with a snapshot of the login page (running the exe from my own ASP.NET app).

Does anybody know how I would get wkhtmltopdf to log into the site so that it can access the page it needs to take a snapshot of?

wkhtmltopdf is installed in the program files directory on the server and is being called via:

public void HtmlToPdf(string website, string destinationFile)
{
ProcessStartInfo startInfo = new ProcessStartInfo();
startInfo.FileName = "wkhtmltopdf.exe";
startInfo.Arguments = website + " " + destinationFile;
Process.Start(startInfo);
}

EDIT -------------

I couldn't get the --cookie-jar method to work (see comments), but I did find another way to programmatically log in with the username/password in the querystring.

I pass the username/pw as params in my querystring and try to access the page I want with wkhtml. When the membership provider kicks me out to the login page, I access the params (which are stored in the url as the returnUrl param) via code-behind and authenticate myself. A simple response.redirect, and bingo -- I've got my PDF snapshot.

// Check to see if an outside program is trying
// to log in by passing creds in the querystring.
if (Request.QueryString["username"] != null) &&
Request.QueryString["password"] != null))
{
string user = Request.QueryString["username"];
string pw = Request.QueryString["password"];
if (System.Web.Security.Membership.ValidateUser(user, pw))
{
// Create an authentication ticket for wkhtml session
System.Web.Security.FormsAuthentication.SetAuthCookie(user, false);
if (Request.QueryString["ReturnUrl"] != null)
{
Response.Redirect(Request.QueryString["ReturnUrl"]);
}
}
else
{
throw new Exception("You failed to log in.");
}
}