Sso: get a forwarded request, show sign in form and redirect to url which is mentoined in the incoming request

Hi

I now use iron router and I want meteor to do the sign in part for the user and then redirect the user to another server. How can I do that?

User goes to external server
That redirects to meteor
I want to present a login screen
On succes, forward to succes url that is defined as a parameter of the incoming request, I suspect I can use Router.go('Http external url'); but how can I read the request param in a blaze template? I only see this server side?

Thank you!