Kerberos

Dovecot supports Kerberos 5 using GSSAPI. The Kerberos authentication mechanism doesn't require having a passdb, but you do need a userdb so Dovecot can lookup user-specific information, such as where their mailboxes are stored.

Note: If you only wish to authenticate clients using their Kerberos passphrase (as opposed to ticket authentication), you will probably want to use PAM authentication with pam_krb5.so instead.

Pre-requisites

This document assumes that you already have a Kerberos Realm up and functioning correctly at your site, and that each host in your realm also has a host keytab installed in the appropriate location.

For Dovecot, you will need to install the appropriate service keys on your server. By default, Dovecot will look for these in the host's keytab file, typically /etc/krb5.keytab, but you can specify an alternate path using the auth_krb5_keytab configuration entry in dovecot.conf. If you wish to provide an IMAP service, you will need to install a service ticket of the form imap/hostname@REALM. For POP3, you will need a service ticket of the form pop/hostname@REALM. When using Dovecot's SASL with MTA, you will need to install service ticket of the form smtp/hostname@REALM.

Example dovecot.conf configurations

If you only want to use Kerberos ticket-based authentication:

auth default {
  mechanisms = gssapi
  userdb static {
    args = uid=vmail gid=vmail home=/var/vmail/%u
  }
}

(In this virtual-hosting example, all mail is stored in /var/vmail/$username with uid and gid set to 'vmail')

If you also want to support plaintext authentication in addition to ticket-based authentication, you will need something like:

auth default {
  mechanisms = plain gssapi
  passdb pam {
  }
  userdb passwd {
  }
}

(Note that in this example, you will also need to configure PAM to use whichever authentication backends are appropriate for your site.)

Client support

Mail clients that support Kerberos GSSAPI authentication include:

Evolution
Mozilla Thunderbird
SeaMonkey
Mutt
UW Pine

Testing

FIXME: This section requires cleanup.

The test:

Setup mutt in /etc/Muttrc to use kerberos using gssapi and imap configuration
- this is done with set imap_authenticators="gssapi"
run kinit (type in password for kerb)
run command mutt
If you get error No Authentication Method
- run command klist (list all kerberos keys) should show imap/HOSTNAME
/etc/hosts has to be set properly so that kerberos can find server.