How to read ruby on rails config values from within the application controller
In Ruby on Rails 3 and above, you can access the config through Rails.application.config
In more recent versions, you can use Rails.configuration instead. For example: Rails.configuration.time_zone.See more in the official manual on configuration
The class method ActionController::Base.session_options returns a hash of the configuration options for the session.
So in your case you want ActionController::Base.session_options[:domain]