[Dovecot] Change password cheme

[Pascal Nobus]

We want to update our password scheme from crypt to SHA256.

Because usernames/passwords are in MySQL I thought this wouldn't be a 
problem.
We have about 3000 users that need to be updated, so make a new password 
for them isn't possible.
I was thinking of an automated script that would update the database 
after every login.

So we did this:
dovecot.conf:
  mail_executable = /usr/local/etc/updatepwd.sh

updatepwd.sh:
  #!/bin/sh
  $USER $PASSWORD|/usr/local/etc/do_updatepwd.pl
  exec /usr/local/libexec/dovecot/imap "$@"


(do_updatepwd.pl is a perl script that makes a sha256 from the second 
argument, and then update the mysql-query)


However: the password is not in the ENVIROMENT anymore.
I changed in dovecot the settings:
  auth_debug = yes
  auth_debug_passwords = yes


Anyone a solution for this?

Best regards,
Pascal