When one imports their existing users & passwords in Piwik, the rules around the user login or the user passwords are not necessarily as restrictive as Piwik.
The proposal is to add a config file setting that when enabled, would not test the password and login for minimum length or accepted characters.
This will be useful when we publish the Apache log to piwik tool :)
(In ) Fixes #2236 New config setting:
; Piwik will check that usernames and password have a minimum length, and will check that characters are "allowed"
; This can be disabled, if for example you wish to import an existing User database in Piwik and your rules are less restrictive
disable_checks_usernames_attributes = 0
See FAQ http://piwik.org/faq/troubleshooting/#faq_112