current_user_provider.rb

  class CurrentUserProvider
    def self.instance
      @instance = Thingy.new
    end

    def around(controller)
      begin
        Thread.current[:current_user] = controller.current_user
        yield
      ensure
        Thread.current[:current_user] = nil
      end
    end
  end

  ActiveSupport.on_load(:action_controller) do
    if defined?(ActionController::Base)
      ActionController::Base.around_action CurrentUserProvider.instance
    end
    if defined?(ActionController::API)
      ActionController::API.around_action CurrentUserProvider.instance
    end
  end