Hello and thanks for reading this 
Talking about this setup 
We noticed a problem.
Univention self-service allows more special characters in the username then Cloudron does.
https://docs.cloudron.io/user-management/#valid-usernames
The following characters are allowed in usernames:
- Alphanumeric characters
- ‘.’ (dot)
- ‘-’ (hyphen)
Now I am looking for a way to restrict the username creation.
While searching I found this blog article:
But after reading this, it does not read like it would do what I need.
Looking forward to read some feedback.
Cheers,
Elias 