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GitHub User: esummers
@Nic - I know your question is very old, but if you want to integrate Rails with Open Directory Apple has some example code. Unfortunately you need to own OS X Server to view it. Apple uses Ruby on Rails to implement their wiki server and profile manager applications. Dig in to the Server.app bundler and look for a folder called webauthd. The ruby code for md5 authentication with Open Directory is in that folder.