Came across this item. With a similar user population we have a similar requirement. Users are authenticated externally using OAuth2 (AWS Cognito). In our case for two reasons:
- provide anonymity for the users on the public forums (the moderators review all content, although sometimes things slip through)
- avoid leaking commercial data on the user base since it is related to product forums.
For a forum of a foundation, there is a similar need but for reasons of anonymity since it relates to journalism. That forum uses internal user directory currently.
Currently we approximately daily look at the users and change their user names such that it is hard to relate the user name with existing user base.
For deletion, a feature is available:
For registration it is currently not out-of-the-box nor could I find a plug-in on Plugin - Discourse Meta.
A plug-in which would assign a user name like PREFIX plus the number of a unique sequence of numbers or hexdigits would be best.