Question

siteA.com calls sitecookie.com/cookies.ashx and sets a cookie “cookiename” for sitecookie.com domain.
Same browser, same window, new tab, siteB.com calls sitecookie.com/cookies.ashx and tries to get the same cookie “cookiename” (again for sitecookie.com domain) but is null.

cookies.ashx implements IHttpHandler, IReadOnlySessionState and conformsTo [WebServiceBinding(ConformsTo = WsiProfiles.BasicProfile1_1)]

So the question is, why is it null and can we retrieve it?

This is how i make requests from siteA and siteB:

 WebClient fs = new WebClient();
            var data = fs.DownloadData("http://sitecookie.com/cookies.ashx");
            var tostring = System.Text.Encoding.ASCII.GetString(data);
            return tostring;

This is how i read cookie in cookies.ashx the return value is a string.

 var cookie = context.Request.Cookies["cookiename"];
            if (cookie != null) return cookie.Value;
            return "false";

This is how i write cookie in cookies.ashx

HttpCookie cookie = new HttpCookie("sso");
            cookie.Value = context.Request.QueryString["token"];
            cookie.Expires = DateTime.Now.AddDays(1);
            context.Response.AppendCookie(cookie);
            return "true";

Answer 1

It turns out this is not possible since every call to http://sitecookie.com/cookies.ashx is treated as a new request and asp.net will initiate a new sessionId. The only way to persists is by storing the sessionid and passing it along on each subsequent requests. For me that solution wont work since I have many clients calling the service and I will not be able to pass sessionid between those clients.