void DoPreAuthenticate ()
{
bool isProxy = (proxy != null && !proxy.IsBypassed (actualUri));
ICredentials creds = (!isProxy || credentials != null) ? credentials : proxy.Credentials;
Authorization auth = AuthenticationManager.PreAuthenticate (this, creds);
if (auth == null)
return;
webHeaders.RemoveInternal ("Proxy-Authorization");
webHeaders.RemoveInternal ("Authorization");
string authHeader = (isProxy && credentials == null) ? "Proxy-Authorization" : "Authorization";
webHeaders [authHeader] = auth.Message;
usedPreAuth = true;
}