Wikimetrics allows you to select a set of users, also known as a "cohort", select a metric to be computed for each of these users, and retrieve the response in JSON or CSV format.
Owner-only
Ez
Applicable project
meta.wikimedia.org
OAuth "callback URL"
https://metrics.wmflabs.org/auth/google
Allow consumer to specify a callback in requests and use "callback" URL above as a required prefix.