For some reason the key used to set the cookie expiration in Rails changed as of 2.3. Now you set it like this:
ActionController::Base.session = {
:expire_after => 1.day()
}
I set this in both config/environments/production.rb and in config/environment.rb just in case it matters, and it seems to work: cookies are now being set with an expiration date, where before they were not.
