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 2.3.8. I guess it will work with 2.3.x versions as well. I am using bundler to manage the gems.
sudo gem install bundler git clone git://github.com/madhums/omniauth-authlogic-demo.git bundle install rake db:migrate script/server
Dont forget to replace your oauth,openid keys and secret in config/initializers/omniauth.rb.
The demo app is at omniauth-authlogic-demo.heroku.com/signin
In the demo app, after authenticating, in the edit profile, you can associate multiple providers with your account.