Grab the user_id either from a param ?s=<encoded user id> || from the Rails session

custom_warden_strategy.rb

module G5
  module Strategies
    class CookieAuthenticable < ::Warden::Strategies::Base
      def valid?
        request.params['s'] || request.cookies['_g5search_session']
      end

      def authenticate!
        user_id = if request.params['s']
          user_id = Util.decode(request.params['s'])[:user_id]
        else
          session = load_g5_session
          session['warden.user.user.key'].last rescue 0
        end
        user = User.find_by_id(user_id)
        user.nil? ? pass : success!(user)
      end

      protected
        def load_g5_session
          session_data = request.cookies['_g5search_session']
          data, digest = session_data.split('--')
          session = Marshal.load(decode64(data)) rescue {}
        end

        def decode64(data)
          data.unpack("m").first
        end
    end
  end
end

Warden::Strategies.add(:cookie_authenticatable, G5::Strategies::CookieAuthenticable)