Non`@gitlab.com` accounts not working in customers.stg.gitlab.com
Problem
The problem is that non @gitlab.com accounts do not work in customers.stg.gitlab.com. This issue arose during a 3rd party security test with NCC group https://gitlab.com/gitlab-com/team-member-epics/access-requests/-/issues/5369.
Proposal
In general it does make sense to restrict testing accounts in customers.stg.gitlab.com to only @gitlab.com accounts, though once per year we need a third party to security test our staging environments. So I don't have a good solution proposal besides possibly outsourcing this access control to our identity provider, Okta?