I need to control access to a Views-generated JSON feed with OAuth (Drupal 6)
With the services and services_views modules, it's possible to repurpose any view into a service with OAuth authentication. 

From my testbed, here's what the URL for the service looks like:

http://services.localhost:8082/sample_endpoint/views/tracker.json


where "sample_endpoint" is the name of the endpoint, "tracker" is the name of the view being provided as a service, and ".json" is the format for the returned content.