Make sure you have a good reason for the check. It will only be accepted to counter vandalism or disruption to Wikimedia wikis. Valid reasons include needing a block of the underlying IP or IP range, disruptive sockpuppetry, vote-stacking, and similar disruption where the technical evidence from running a check would prevent or reduce further disruption.
Be specific in your reasons. Ambiguous or insufficient reasons will cause delays. Explain the disruption and why you believe the accounts are related, ideally using diff links or other evidence.
Make sure there are no local checkusers or policies.
Reason(s): This user uploaded a video demonstrating IP address change to evade an ISP-level blackholing of Phabricator (gerrit:368775). We've identified a number of ISP addresses from public records for Maroc Telecom phab:Z567#10425, but need assistance in finding more ranges. Dispenser (talk) 18:11, 25 August 2017 (UTC)
Deferred to c:COM:RFCU. Hello. Commons has their own CheckUsers, you should request them on their request page. Regards, —MarcoAurelio (talk) 10:03, 26 August 2017 (UTC)
I cannot really answer that question because I do not know if OAuth logins leave CU trace. I think they don't, but I'll ping @Tgr (WMF) and BDavis (WMF) for clarification. In any case, I think Phabricator administrators can access IP data about users so if there's sockpuppetry problems over there maybe @AKlapper (WMF) and MModell (WMF) will be able to assist. —MarcoAurelio (talk) 09:53, 27 August 2017 (UTC)
Indeed they don't (although the user had to login to MediaWiki at some point, that you could look up). We can add something to the system logs if you think that would be important, feel free to open a phab task about it. Creating MediaWiki log records would be too much effort compared to how rarely it would be useful, IMO. (Also probably not something CUs should have access to, as OAuth authentication can be used for third-party logon and whatnot.) --Tgr (WMF) (talk) 20:26, 27 August 2017 (UTC)
I'll have a look at those on mediawiki. —MarcoAurelio (talk) 10:33, 28 August 2017 (UTC)
There are not conclusive results at mediawiki. They might be sockpuppets based on what they do, but so far the only connection I see is continental procedence, which is not much. The ranges are also crowded to do a safe IP range block. If someone else with more experience does want to have a look, feel free. —MarcoAurelio (talk) 11:27, 28 August 2017 (UTC)
I've filed a phabricator task. Cleaning up phabricator requires console commands which is why a /8, /11s, and /12s are blackholed, but they still somehow got through two filters. Dispenser (talk) 13:04, 28 August 2017 (UTC)
Is it possible to setup an abuser filter to tag accounts created here (Meta) as a WP0 user (or Moroccan IP or a proxy we blocked on Commons like Azure)? Is it possible to have an idea of where those accounts are created?