How to limit allowed usernames on account creation on Jira?

[Sorin Sbarnea (Citrix)]

I want to force people to use certain format for their username when they register to Jira.

This is needed because the server is using several external authentications directories and I want to be sure that they do not overlap.

[Nic Brough -Adaptavist-]

You'll need to add some code to the account creation process to do this. I've not seen any plugins that will do it - most of the time people delegate the whole thing to the other system(s) so the accounts are handled automatically.