[Dovecot] Changing password for users

[Mike John]

Hello,

I am using dovecot (2.0.9) and using virtual users using
passdb {
  args = /etc/dovecot/dovecotpasswd
  driver = passwd-file
}

How can i make my virtual users change their passwords using web 
interface ?

My users already uses squirrelmail to access their mail. is there a 
program to add to squirrelmail to add this function to the clients ? or 
should i user different separate website for password changing ? and 
what program/tool can help me with this ?

Any ideas is greatly appreciated.

Mike.