I'd put it into a class under lib/ and not into a controller;
controllers shall be thin and glue the view and the model. it depends
how you "see" your external resource; you can look at it like a model.
a bit more important could be the fact that external access to the
resource will lock-up your users request and bind one of your mongrel
(or rails instances) to that request. you can use backgroundrb (http://
backgroundrb.rubyforge.org/) for such cases and communicate
asynchronously with your external system.