secure_action is a ruby on rails plugin which makes it easy to defend your site against assumed logged in attacks.
To install, check out the code in your RAILS_ROOT/vendor/plugins/ directory and follow the instructions in the README:
svn checkout http://secure-action-plugin.googlecode.com/svn/trunk/ secure-action-plugin
Interesting article from a developer
svn checkout http://checkout-on-rails.googlecode.com/svn/trunk/ checkout-on-rails