[Dovecot] critical feature from version 1 not migrated to version 2 = authentication configuration database per IP

[DaLiV at apollo.lv]

not possible make operation with dovecot version 2.x as was possible in version 1.x:

requisites description:

connect to dovecot service on IP1 - dovecot must serve users that related to domain1 located in database1
connect to dovecot service on IP2 - dovecot must serve users that related to domain2 located in database2

login must be with username that form not as "user at domain" but simple "user"

databases may contain identical username, but they have different passwords

existing version 1 config file, that allow such configuration:
-------- /etc/dovecot.conf BEGIN ----------------
server mail.domain1.tld {
protocols = imaps pop3s pop3
ssl_cert_file = /etc/pki/cert1.pem
ssl_key_file = /etc/pki/cert1.key
listen = 123.123.123.1
ssl_listen = 123.123.123.1
default_mail_env = mbox:/tmp:INBOX=/var/mail/domain1.tld/%n:INDEX=MEMORY
   pop3_uidl_format = %08Xu%08Xv
auth default {
   mechanisms = plain

   passdb ldap {
     args= /etc/dovecot-ldap.conf.domain1.tld1
   }
   userdb ldap {
     args= /etc/dovecot-ldap.conf.domain1.tld1
   }
}
login_process_per_connection = yes
login_max_processes_count = 4
login_processes_count = 1
}
server mail.domain2.tld {
protocols = imaps pop3s pop3
ssl_cert_file = /etc/pki/cert2.pem
ssl_key_file = /etc/pki/cert2.key
listen = 123.123.123.2
ssl_listen = 123.123.123.2
default_mail_env = mbox:/tmp:INBOX=/var/mail/domain2.tld/%n:INDEX=MEMORY
   pop3_uidl_format = %08Xu%08Xv
auth default {
   mechanisms = plain

   passdb ldap {
     args= /etc/dovecot-ldap.conf.domain2.tld2
   }
   userdb ldap {
     args= /etc/dovecot-ldap.conf.domain2.tld2
   }
}
login_process_per_connection = yes
login_max_processes_count = 4
login_processes_count = 1
}
-------- /etc/dovecot.conf END ----------------

/etc/dovecot-ldap.conf.domain1.tld and /etc/dovecot-ldap.conf.domain2.tld
refers to different ldap databases