gistfile1.rb

#:key not :session_key in latest edge

#in assets_helper.rb
def new_asset_path_with_session_information
  session_key = ActionController::Base.session_options[:key]
  new_asset_path(session_key => cookies[session_key], request_forgery_protection_token => form_authenticity_token)
end

…

#in config/initializers/session_store.rb
ActionController::Base.session = {
  :key => '_my_app_session',
  :secret      => '--blah--' # Real key removed to protect the innocent
}

ActionController::Dispatcher.middleware.use FlashSessionCookieMiddleware, ActionController::Base.session_options[:key]