[Dovecot] Master User Features I'd like to see

[Marc Perkel]

  Here's what I'd like. Limited master users, where someone can be a 
master users for some domains but not others. I think I could do what I 
want with the right kinds of variable passing that doesn't yet exist. 
Let me see if I can explain clearly.

 From the example in the wiki:

auth_master_user_separator = *
passdb {
   driver = sql
   args = /etc/dovecot/dovecot-sql-master.conf.ext
   master = yes
   pass = yes
}
passdb {
   driver = sql
   args = /etc/dovecot/dovecot-sql.conf.ext
}
userdb {
   driver = sql
   args = /etc/dovecot/dovecot-sql.conf.ext
}

Login looks like this:
# telnet localhost 143
* OK Dovecot ready.
1 login loginuser*masteruser masterpass
1 OK Logged in.


I'm assuming that the masteruser and masterpass is passed to the master 
passdb and when doing so the variable %u is the master user.  I assume 
that %n and %d also represent the name and domain part of the master user.

What I need is to also be able to have variables for the loginuser 
passed to the master user query. Something like %lu, %ln, and %ld 
perhaps. That way with MySQL tricks I might be able to see if the master 
user is master for that particular login user. That way I can give 
domain owners or owners of multiple domains the ability to manage the 
email accounts within their scope of permission.