extract_session_id

# File actionpack/lib/action_dispatch/middleware/session/abstract_store.rb, line 200
        def extract_session_id(env)
          stale_session_check! do
            request = ActionDispatch::Request.new(env)
            sid = request.cookies[@key]
            sid ||= request.params[@key] unless @cookie_only
            sid
          end
        end