Management user password
Deaar Admin Redmine,
I have an idea, what if the user's password has the active period and the user can change the password
Another Redmine user here.
The user can change their password under My Account (change password link) or on an LDAP.
There are a bunch of options under Administration -> Settings -> Authentication. Your idea would probably go there. Look at the self registration options.
Otherwise, you probably could use an LDAP server to control the password duration without locking the account.