An un-authenticated user tries to visit http://www.mysite.com/Support/Overview.aspx?a=1&b=2&c=3 

They land at the login page with a URL of: https://www.mysite.com/Login.aspx?returnurl=/Support/Overview.aspx?a=1&b=2&c=3 

After logging in the user ends up at a page that is missing the 2nd and 3rd URL params: http://www.mysite.com/Support/Overview.aspx?a=1 

I sort of understand what's going on - I've got a URL embedded withing a URL and it's getting confused by that second question mark. 

The redirect will work if the returnURL format is encoded to be: ?returnUrl=%2FSupport%2FOverview.aspx%3Fa%3D1%26b%3D2%26c%3D3 

How can I get this to work? 

Thanks, Greg