load_session

# File actionpack/lib/action_controller/session/abstract_store.rb, line 168
        def load_session(env)
          request = Rack::Request.new(env)
          sid = request.cookies[@key]
          unless @cookie_only
            sid ||= request.params[@key]
          end
          sid, session = get_session(env, sid)
          [sid, session]
        end