q: cookies, expire

hi
as far as i know, if u want to have a cookie expired on a browser
close, u set the expire object to zero. if this is correct, where
would i do that in rails3?

and which code would that be?
cookies.signed[:login] = {:value => @user.id, :expires => Time.now}
request.session_options[:expire_after]

the docs are a bit unclear.
thx