user_session.rb

# encoding: utf-8
module UserSession

  extend self

  USER_KEY    = "user".freeze
  SESSION_KEY = "session_id".freeze

  class Rack

    def initialize(app)

      @app = app
      @key = ::Rails.application.config.session_options[:key]

    end # initialize

    def call(env)

      @request = ::Rack::Request.new(env)
      register_user
      @app.call(env)

    end # call

    private

    def register_user

      return unless changed?

      @user_before        = @request.session[::UserSession::USER_KEY]
      @session_id_before  = @request.session[::UserSession::SESSION_KEY]
      ::Thread.current[::UserSession::token] = (::User.auth_by_cookie(@request.session[::UserSession::USER_KEY]) || ::User.new)

      nil

    end # register_user

    def changed?

      return true if @user_before.nil?
      return true if @user_before != @request.session[::UserSession::USER_KEY]
      return true if @session_id_before != @request.session[::UserSession::SESSION_KEY]

      false

    end # changed?

  end # Rack

  def current
    ::Thread.current[::UserSession::token] || ::User.new
  end # current

  def token
    ::Anlas::Application.config.secret_token
  end # token

end # UserSession

В файле application.rb добавляем
config.middleware.use ::UserSession::Rack

Затем в любом месте проекта вызываем ::UserSession.current