*Description
This extension adds support for password expiration.
It is designed to have expiration on users passwords. An email is sent when the password is expiring in 30 days, then 14 days, then 7 days.
It is strongly inspired by https://abridge2devnull.com/posts/2014/09/29/dovecot-user-password-expiration-notifications-updated-4122015/, and adapted to fit with Postfix Admin & Roundcube's password plugin

*Installation
Perform the following changes:

**Changes in MySQL/MariaDB mailbox table (as defined in $CONF['database_tables'] from config.inc.php):
You are invited to backup your DB first, and ensure the table name is correct.

Execute the attached SQL script (password_expiration.sql) that will add the required columns. The expiration value for existing users will be set to 90 days. If you want a different value, edit the last line in the script and replace 90 by the required value.

**Changes in Postfix Admin :
To enable password expiration, add the following to your config.inc.php file:
$CONF['password_expiration_enabled'] = 'YES';

Do not forget to set the expiration value (in days)
$CONF['password_expiration_value'] = '90';

All my tests are performed using $CONF['encrypt'] = 'md5crypt';

**If you are using Roundcube's password plugin, you should also adapt the $config['password_query'] value.
I recommend to use:
$config['password_query'] = 'UPDATE mailbox SET password=%c, modified=now(),pw_expires_on=now() + interval 90 day, thirty=0,fourteen=0,seven=0 where username=%u';
of cource you may adapt to the expected expiration value

All my tests are performed using $config['password_algorithm'] = 'md5-crypt';

**Changes in Dovecot (adapt if you use another LDA)
Edit dovecot-mysql.conf file, and replace the user_query (and only this one) by this query:
user_query = SELECT concat('/var/vmail/', maildir) as home, concat('maildir:/var/vmail/', maildir) as mail, 20001 AS uid, 20001 AS gid, concat('dirsize:storage=', quota) AS quota FROM mailbox WHERE username = '%u' AND active = '1' AND pw_expires_on > now()
if course you may require to adapt the uid, gid, maildir and table to your setup

**Changes in system
You need to have a script running on a daily basis to check password expiration and send emails 30, 14 and 7 days before password expiration (script attached: check_mailpass_expiration.sh).
Edit the script to adapt the variables to your setup.
Ensure the user running check_mailpass_expiration.sh is allowed to access (read-write) your database.
