Using Sap Enterprise Portal redirecting

Hello All,

I try to using Sap Enterprise Portal redirecting on to HTTP and we want it to redirect it to a Secure HTTP for example google.com, we are using SAP Web Dispatcher and SSO is used for logon in Sap Portal.

My problem is when I logon in sap portal and I have a sesion open, I can used This URL

http://web_dispatcher/redirect/redirect?url=irj/servlet/prt/portal/prtroot/VestasRedirectApp.vestasRedirect?redirectURL=http://www.google.com

And logon in google.com ,

But If I have not any sesion open I get this login screen.

Image may be NSFW.
Clik here to view.

Any Idea what I need to logon in  google.com without had any sesion open in Sap portal first.

Thanks for any help

Reza