Omniauth is a pretty simple solution if you want your users to authenticate using oauth and openid providers. Here I am using authlogic to manage the user sessions and omniauth to do the external authentication.
I have tested this with rails 2.3.11 (rails 2.3.8 gives some issues, sorry can't remember which)
Unfortunately omniauth doesn't support 2.3.x (according to this omniauth/issues/244#issuecomment-1055851 ), but there are some workarounds which I have added, refer changelog
gem install bundler
git clone git://github.com/madhums/omniauth-authlogic-demo.git
bundle install
rake db:migrate
script/server
Important : Dont forget to replace your oauth,openid keys and secret in config/initializers/omniauth.rb.
The demo app is at http://omniauth-authlogic-demo.heroku.com/signin
In the demo app, after authenticating, in the edit profile, you can associate multiple providers with your account.