[Dovecot] related, but off-topic: how to allow users to change password?

[Sahil Tandon]

My dovecot is currently configured to authenticate vs. a userdb/passdb 
passwd-file that contains, for each user:

username:passhash:5000:5000::/path/to/home::userdb_mail=/path/to/maildir
                                       
Is it possible to let users authenticate and change their passwords?  There 
are some webmail client add-ons that allow such things if users are system 
accounts or in a MySQL/LDAP db.  Does anyone else use passdb/userdb 
passwd-files like above and have a method for allowing users to change their 
passwords from the web?

Sorry for the slightly off-topic question, but hoping another Dovecot admin 
has solved this problem.  Preference is to not to be tied to any particular 
webmail client just for this change password feature.