How to define custom configuration variables in rails

Update 1

Very recommended: I'm going with Rails Config gem nowadays for the fine grained control it provides.

Update2

If you want a quick solution, then check Jack Pratt's answer below.

Although my original answer below still works, this answer is now outdated. I recommend looking at updates 1 and 2.

Original Answer:

For a quick solution, watching the "YAML Configuration File" screen cast by Ryan Bates should be very helpful.

In summary:

# config/initializers/load_config.rb
APP_CONFIG = YAML.load_file("#{Rails.root}/config/config.yml")[Rails.env]

# application.rb
if APP_CONFIG['perform_authentication']
  # Do stuff
end

In Rails 3, Application specific custom configuration data can be placed in the application configuration object. The configuration can be assigned in the initialization files or the environment files -- say for a given application MyApp:

MyApp::Application.config.custom_config_variable = :my_config_setting

or

Rails.configuration.custom_config_variable = :my_config_setting

To read the setting, simply call the configuration variable without setting it:

Rails.configuration.custom_config_variable
=> :my_config_setting

UPDATE Rails 4

In Rails 4 there a new way for this => http://guides.rubyonrails.org/configuring.html#custom-configuration