R – When retrieving URL via HttpWebRequest, can I see the IP address of the destination server

Looks ok to me. I recommend using Wireshark to see what your restclient is sending in the headers and and see what your app sending in the headers.

The .NET framework will manage cookies for you. You don't have to concern yourself with parsing the cookie information out of the headers or adding a cookie header to your requests.

To store and send your session ID, use the Cookie and CookieContainer classes to store them and then make sure you send your cookies with every request.

The following example shows how to do this. The CookieContainer, 'cookieJar' can be shared across multiple domains and requests. Once you add it to a request object, the reference to it will also be added to the response object when the response is returned.

CookieContainer cookieJar = new CookieContainer();

var request = (HttpWebRequest)HttpWebRequest.Create("http://www.google.com");
request.CookieContainer = cookieJar;

var response = request.GetResponse();

foreach (Cookie c in cookieJar.GetCookies(request.RequestUri))
{
    Console.WriteLine("Cookie['" + c.Name + "']: " + c.Value);
}

The output of this code will be:

Cookie['PREF']: ID=59e9a22a8cac2435:TM=1246226400:LM=1246226400:S=tvWTnbBhK4N7Tlpu