http://stackoverflow.com/questions/5161522/where-to-store-structured-configuration-data-in-rails/5161592#5161592

config_application.yml

# All values should be specified in "default". Anything
# that is specified in any other environment--"test", "development",
# or "production"--will overwrite values in "default".

default:
  allow_registration: false
  facebook:
    app_id: APP_ID_HERE
    app_secret: APP_SECRET_HERE
    api_key: API_KEY_HERE
  twitter:
    api_key: API_KEY_HERE
    oauth_consumer_key: CONSUMER_KEY_HERE
    oauth_consumer_secret: CONSUMER_SECRET_HERE

development:
  allow_registration: true

test:
  allow_registration: true

config_initializers_app-config.rb

require 'yaml'

# ERB.new allows us to use ERB tags in the YAML
yaml_data = YAML::load(ERB.new(IO.read(File.join(Rails.root, 'config', 'application.yml'))).result)

# Merge the "default" section with the section for this environment
config = yaml_data["default"]
begin
  config.merge! yaml_data[Rails.env]
rescue TypeError
  # nothing specified for this environment; do nothing
end

# Pass to a HashWithIndifferentAccess so that we can use symbols (APP_CONFIG[:key])
APP_CONFIG = HashWithIndifferentAccess.new(config)