Ldap & build in users at one instance of RM and single auth plugin

I have issue with your plugin. I am using two types of accounts: one for users from active directory - for regular employees of company, second build in redmine accounts for outsource and partners.

After installed your plugin, people who are not log in to redmine by Windows Domain (NTLM) doesn't have access to RM (the same situation is for Linux users). 

How to bypass this issue?
