This security fix affects sites which have `SiteSetting.must_approve_users`
enabled. There are intentional and unintentional cases where invited
users can be auto approved and are deemed to have skipped the staff approval process.
Instead of trying to reason about when auto-approval should happen, we have decided that
enabling the `must_approve_users` setting going forward will just mean that all new users
must be explicitly approved by a staff user in the review queue. The only case where users are auto
approved is when the `auto_approve_email_domains` site setting is used.
Co-authored-by: Alan Guo Xiang Tan <gxtan1990@gmail.com>
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