We've noticed that getting a working OAuth library installed isn't as straight-forward as we'd like. It's hard to get libraries installed and many of them don't support the subset of OAuth that Rdio uses. In response we've developed a set of very simple libraries for PHP, Python and Ruby that implement the parts of OAuth that Rdio uses, plus basic methods for authenticating against Rdio and calling methods on the Rdio Web Service.
We hope that these will help developers get up and running on the Rdio platform quickly.
More documentation is available here: http://developer.rdio.com/docs/read/rest/rdiosimple
And the source code is here: https://github.com/rdio/rdio-simple