ASP.NET How to pass a value to another site?

Question

I have two separate websites. The main site requires a login. A menu on my website should redirect the user to a different website and pass to it the username of the logged in user. I have the following code:

Main website (sending):

using (var client = new WebClient())
{
    var values = new NameValueCollection();
    values["user"] = Session["UserName"].ToString();
    client.UploadValues("http://spsrv02:93/", values);
}

Other website (receiving):

string value = Request.Form["user"];

I am getting this error: "ERR_TOO_MANY_REDIRECTS"

Please help. What am I doing wrong?

P.S I don't want to go through URL parameters since I will have to encrypt/decrypt the data and I don't want to get into that whole cryptography deal.

I tried debuggin with VS but I can't redirect to a local running IIS page