Kerberos
========

Dovecot supports Kerberos 5 using GSSAPI. The Kerberos authentication mechanism
doesn't require having a<passdb> [PasswordDatabase.txt], but you do need a
<userdb> [UserDatabase.txt] 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> [PasswordDatabase.PAM.txt] 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> [Sasl.txt] 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.txt>
 * Mutt
 * UW Pine

Testing
-------

*FIXME*: This section requires cleanup.

Test that the server can access the keytab
------------------------------------------

This test demonstrates that te server can acquire its private credentials.
First telnet directly to the server

 * ---%<----------------------------------------------------------------------
   $ telnet localhost 143
   * OK Dovecot ready.
   ---%<----------------------------------------------------------------------

or, if you are using IMAPS then use openssl instead of telnet to connect:

 * ---%<----------------------------------------------------------------------
   $ openssl s_client -connect localhost:993
   CONNECTED(00000003)
   ...
   * OK Dovecot ready.
   ---%<----------------------------------------------------------------------

Check that GSSAPI appears in the authentication capabilities:

 * ---%<----------------------------------------------------------------------
   a capability
   * CAPABILITY ... AUTH=GSSAPI
   ---%<----------------------------------------------------------------------

Attempt the first round of GSS communication. The '+' indicates that the server
is ready

 * ---%<----------------------------------------------------------------------
   a authenticate GSSAPI
   +
   ---%<----------------------------------------------------------------------

Abort the telnet session by typing control-] and then 'close'

 * ---%<----------------------------------------------------------------------
   ^]
   telnet> close
   ---%<----------------------------------------------------------------------

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. 

(This file was created from the wiki on 2009-02-04 04:42)
