Document what "No Support of on-the-fly registration" means

[isrc]

Hi,
Thanks for this redmine plugin
!
The Readme is short and precise but It would be nice if you could add a line or two telling what are the implication of "no support of on-the-fly registration" regarding the redmine configuration process please.
Newbie here, so please tell me if i'm wrong, but it seems that in order to successfully authenticate CAS users with this plugin, the redmine administrator has to:

• disable "Minimum password length" requirement (set it to '0') in "Administration > Settings > Authentication". Required for the second step below
• and Create (or better import if that's possible) all the CAS users login via the redmine "Administration > Users > New user" settings

Failing to do so, results in the redmine authentication process failing with this error message (in redmine/logs/production.log) "Failed login for '<redacted_cas_user_login'> from at 2013-10-16 03:15:24 UTC
Redirected to http://<redacted_redmine_hostname>/login"

Am i wrong ?
How do you guys import en masse your CAS users into Redmine please ?

Thanks.