How do I store querystring values in session?

Experts,
What I am trying to do is similar to what happens when you attempt to start a new post here.
If you click on Start A New Post without logging in first, you are taking to login screen. If your login is successful, you are redirected back to your original page to start your new post.
In my case, here is what I am trying to doing:
A user is presented with summary page.
User clicks a link below:
<asp:HyperLink ID="hdReserve" class="js_siteid" AutoPostBack="false" runat="server" Text="Select" Navigateurl='<%# String.Format("requestSummary.aspx?id={0}&groupsize={1}&facilityFees={2}&depoitAmt={3}&cancelAmt={4}&keydeptAmt={5}&extrahour={6}&facility={7}&hoursdiff={8}", CType(Container.DataItem, System.Data.DataRowView)("siteId") , ddlPartySize.SelectedValue,CType(Container.DataItem, Sy ...