Where to put constraint classes in Rails project

Just curious about the best practices for Rails in where I put a custom constraints class that's used as a constraint in config/routes.rb. Seems like Rails.root/lib is where all user classes go. Is that appropriate for this? Should I be creating a directory inside for constraints? 2 empty directories exist there now, assets and tasks. Are there conventions for this?

lib/ would be the appropriate place. If you want to make it cleaner, put it in lib/constraint/authenticated.rb and define your constraints like so

module Constraint
  class Authenticated
    def matches?(request)
      # stuff
    end
  end
end

and in your routes.rb

constraints Constraint::Authenticated.new do
  match 'account' => 'account#index'
end