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Passdb LDAP with authentication binds
=====================================

Advantages over <password lookups> [AuthDatabase.LDAP.PasswordLookups.txt]:

 * LDAP server verifies the password, so Dovecot doesn't need to know what
   format the password is stored in.
 * A bit more secure, as a security hole in Dovecot doesn't give attacker
   access to all the users' password hashes. (And Dovecot admins in general
   don't have direct access to them.)

You can enable authentication binds by setting 'auth_bind=yes'. Next Dovecot
needs to know what DN to use in the binding. There are two ways to configure
this: lookup or template.

DN lookup
---------

DN is looked up by sending a 'pass_filter' LDAP request and getting the DN from
the reply. This is very similar to doing a <password lookup>
[AuthDatabase.LDAP.PasswordLookups.txt]. The only difference is that
userPassword attribute isn't returned. Just as with password lookups, the
'pass_attrs' may contain special <extra fields>
[PasswordDatabase.ExtraFields.txt].

Example:

---%<-------------------------------------------------------------------------
auth_bind = yes
pass_attrs = uid=user
pass_filter = (&(objectClass=posixAccount)(uid=%u))
---%<-------------------------------------------------------------------------

DN template
-----------

The main reason to use DN template is to avoid doing the DN lookup, so that the
authentication consists only of one LDAP request. With IMAP and POP3 logins the
same optimization can be done by using <prefetch userdb>
[UserDatabase.Prefetch.txt] and returning userdb info in the DN lookup (a total
of two LDAP requests per login in both cases). If you're also using Dovecot for
SMTP AUTH, it doesn't do a userdb lookup so the prefetch optimization doesn't
help.

If you're using DN template, 'pass_attrs' and 'pass_filter' settings are
completely ignored. That means you can't make passdb return any <extra fields>
[PasswordDatabase.ExtraFields.txt]. You should also set 'auth_username_format =
%Lu' in 'dovecot.conf' to normalize the username by lowercasing it.

Example:

---%<-------------------------------------------------------------------------
auth_bind = yes
auth_bind_userdn = cn=%u,ou=people,o=org
---%<-------------------------------------------------------------------------

Connection optimization
-----------------------

When using

 * auth binds and
 * userdb ldap lookups,

the userdb lookups should use a separate connection to the LDAP server. That
way it can send LDAP requests asynchronously to the server, which improves the
performance. This can be done by specifying different filenames in the LDAP
passdb and userdb args. The second file could be a symlink to the first one.
For example:

---%<-------------------------------------------------------------------------
passdb {
  driver = ldap
  args = /etc/dovecot/dovecot-ldap.conf.ext
}
userdb {
  driver = ldap
  args = /etc/dovecot/dovecot-ldap-userdb.conf.ext
}
---%<-------------------------------------------------------------------------

And create the symlink:

---%<-------------------------------------------------------------------------
ln -s /etc/dovecot/dovecot-ldap.conf.ext
/etc/dovecot/dovecot-ldap-userdb.conf.ext
---%<-------------------------------------------------------------------------

(This file was created from the wiki on 2019-06-19 12:42)