You could do something really simple and have a HTTP basic auth before-filter:
class ApplicationController < ActionController::Base
before_filter :beta_protection
def beta_protection
return true unless Rails.env.beta?
authenticate_or_request_with_http_basic do |username, password|
username == "username" && password == "password"
end
end
end
This won't look super great, but you can use this (and give the username and password out to beta users) to add in a simple, easy way to control access to your site.