Using oauth_common in a module to authenticate with a web service? I'm wanting to use my Drupal 7 site to communicate with an external API that must be authenticated via 3-legged OAuth. 

It seems there's a lot of documentation around about using Drupal as the OAuth provider (Via the OAuth project), but very little about using its API to do things like authenticate a Drupal site with an external web service. There's an old complete tutorial, but this doesn't list any of the functions that oauth_common provides, nor even really any code with how to build an OAuth session with the module.

Any help? Moreover, is there a "Drupal Way" of creating OAuth sessions?

(If it helps, I'm doing stuff with Magento and using the examples here as a base.)
Have you ever try to use OAuth Connector. It allows us to create the comsumer/application/connection to Twitter, Facebook... or another Drupal website. For my own purpose. I used that for fetch the data from Drupal 6 Services 3 by using this module in Drupal 7 and some extra code and it worked fine.