Wikimedia Bugzilla is closed!

The current documentation is:

* action=uploadcampaign *
  API module for fetching data on Upload Campaigns, associated with UploadWizard.
  Do not rely on this, it is an API method mostly for developer convenience and
  may change without warning.

This module requires read rights
Parameters:
  campaigns           - The name(s) of the campaign(s) to fetch info on. If empty, all campaigns will be fetched.
                        Separate values with '|'
                        Maximum number of values 50 (500 for bots)
  ucprop              - 
                        Values (separate with '|'): config
                        Default: 
Examples:
  api.php?action=uploadcampaign
  api.php?action=uploadcampaign&campaigns=wlm-at|wlm-es

So no info about valid ucprop values. Things like https://commons.wikimedia.org//w/api.php?action=uploadcampaign&format=json&ucprop=config should be documented (more hidden features?)