Currently, you can use the API to search for a list of users using usernames (the ususers propery). However, there is no way to search using their user ids instead.
It would be nice if such a parameter existed (or the ususers property was updated to also accept a list of user ids)
(Current API info is at https://www.mediawiki.org/wiki/API:Users)
Version: 1.20.x
Severity: enhancement