See T402597: Exploratory testing on PHP 8.3 for MediaWiki Platform Team components for context. T384232: QA for SUL3 on testwikis has more info on some checklist items.
Central session
- after login or signup, user should be logged in on other registrable domains (on browsers which don't block 3rd-party cookies)
- "keep me logged in" state is transferred correctly
- after deleting cookies on a given domain, centrally logged-in user should autologin (on browsers which don't block 3rd-party cookies)
- after deleting cookies on a given domain and setting CentralAuthAnon=1 cookie, centrally logged-in user should autologin when clicking login link
- after temp user creation, temp user should be logged in on other registrable domains, with "keep me logged in" set (on browsers which don't block 3rd-party cookies)
- after deleting cookies on a given domain, centrally logged-in temp user should autologin (on browsers which don't block 3rd-party cookies)
- after deleting cookies on a given domain and setting CentralAuthAnon=1 cookie, centrally logged-in temp user should autologin when clicking login link
- logout clears the centralauth_* cookies on registrable domains other than the current one