We needed a Single Sign-On (SSO) solution for multiple Apache machines. We discovered the mod_auth_tkt module and it was exactly what we wanted. A cookie is generated during the authorisation process and signed with a shared secret. This shared secret (aside with the mod_auth_tkt module) is the only requirement to resctrict access to multiple Apache machines to users, who have a valid ticket stored in a signed cookie.
But we wanted to use Ruby on Rails to generate this cookie.
We usually use Acts as Authenticated and acl_system2 for the authentication process, so we integrated our library into this plugin. Only six additional lines in two files where needed therefor. Which lines to add and where to add is described in the readme file that comes with the auth_tkt_rails library.
The integration is described in the auth_tkt_rails readme file.