[Dovecot] can't deliver with Kerberos username

[Nikolay Shopik]

I've been trying to use Kerberos and PLAIN text file for authentication. 
I've setup deliver in postfix master.cf and make sure correct username 
are expanded but deliver is always told me "user unknown".
I can logon into mailbox using Kerberos w/o problems and can send 
emails. Looks like Dovecot lookup up passwd files and not finding users 
which are in Kerberos realm.


# 1.0.15: /etc/dovecot/dovecot.conf
log_path: /var/log/dovecot.log
protocols: imap
ssl_cert_file: /etc/postfix/new_chained.crt
ssl_key_file: /etc/postfix/mail.pem
login_dir: /var/run/dovecot/login
login_executable: /usr/lib/dovecot/imap-login
login_greeting_capability: yes
mail_location: maildir:/var/mail/store/%u
dotlock_use_excl: yes
maildir_copy_with_hardlinks: yes
auth default:
   mechanisms: PLAIN CRAM-MD5 GSSAPI
   passdb:
     driver: passwd-file
     args: /etc/dovecot/passwd
   userdb:
     driver: static
     args: uid=vmail gid=vmail home=/var/mail/store/%u
   socket:
     type: listen
     client:
       path: /var/spool/postfix/private/auth
       mode: 432
       user: postfix
       group: postfix
     master:
       path: /var/run/dovecot/auth-master
       mode: 438
       user: root
       group: root
plugin:
   sieve: /var/mail/store/%u/sieve