```ruby
# TODO store staff user via Warden
module UserImpersonate
  module DeviseHelpers
    module Helpers
      # current_user changes from a staff user to
      # +new_user+; current user stored in +session[:staff_user_id]+
      def impersonate(new_user)
        session[:staff_user_id] = current_staff.id # 
        sign_in new_user, bypass: true
      end
      
      # revert the +current_user+ back to the staff user
      # stored in +session[:staff_user_id]+
      def revert_impersonate
        return unless current_staff_user
        sign_in current_staff_user, bypass: true
        session[:staff_user_id] = nil
      end
    end
    
    module UrlHelpers
      def current_staff_user
        return unless session[:staff_user_id]
        user_finder_method = config_value(UserImpersonate::Engine.config, :user_finder, 'find').to_sym
        user_class_name = config_value(UserImpersonate::Engine.config, :user_class, 'User')
        user_class = user_class_name.constantize
        @staff_user ||= user_class.send(user_finder_method, session[:staff_user_id])
      end

      private

      def config_value(config, sym, default)
        config.respond_to?(sym) ? (config.send(sym) || default) : default
      end
    end
  end
end
```

Replace deprecated devise bypass option
user
```ruby
# TODO store staff user via Warden
module UserImpersonate
  module DeviseHelpers
    module Helpers
      # current_user changes from a staff user to
      # +new_user+; current user stored in +session[:staff_user_id]+
      def impersonate(new_user)
        session[:staff_user_id] = current_staff.id # 
        bypass_sign_in new_user
      end

      # revert the +current_user+ back to the staff user
      # stored in +session[:staff_user_id]+
      def revert_impersonate
        return unless current_staff_user
        bypass_sign_in current_staff_user
        session[:staff_user_id] = nil
      end
    end

    module UrlHelpers
      def current_staff_user
        return unless session[:staff_user_id]
        user_finder_method = config_value(UserImpersonate::Engine.config, :user_finder, 'find').to_sym
        user_class_name = config_value(UserImpersonate::Engine.config, :user_class, 'User')
        user_class = user_class_name.constantize
        @staff_user ||= user_class.send(user_finder_method, session[:staff_user_id])
      end

      private

      def config_value(config, sym, default)
        config.respond_to?(sym) ? (config.send(sym) || default) : default
      end
    end
  end
end
```
assistant