openldap/contrib/slapd-modules/nssov/README

Copyright 2008-2009 Howard Chu, Symas Corp. All rights reserved.

Redistribution and use in source and binary forms, with or without
modification, are permitted only as authorized by the OpenLDAP
Public License.

A copy of this license is available in the file LICENSE in the
top-level directory of the distribution or, alternatively, at
<http://www.OpenLDAP.org/license.html>.

This directory contains a slapd overlay, nssov, that handles
NSS lookup requests through a local Unix Domain socket. It uses the
same IPC protocol as Arthur de Jong's nss-ldapd, and a complete
copy of the nss-ldapd source is included here. It also handles
PAM requests.

To use this code, you will need the client-side stub library from
nss-ldapd (which resides in nss-ldapd/nss). You will not need the
nslcd daemon; this overlay replaces that part. You should already
be familiar with the RFC2307 and RFC2307bis schema to use this
overlay. See the nss-ldapd/README for more information on the
schema and which features are supported.

To use the overlay, add:

	include <path to>nis.schema

	moduleload <path to>nssov.so
	...

	database hdb
	...
	overlay nssov

to your slapd configuration file. (The nis.schema file contains
the original RFC2307 schema. Some modifications will be needed to
use RFC2307bis.)

The overlay may be configured with Service Search Descriptors (SSDs)
for each NSS service that will be used. SSDs are configured using

	nssov-ssd <service> <url>

where the <service> may be one of
	alias
	ether
	group
	host
	netgroup
	network
	passwd
	protocol
	rpc
	service
	shadow

and the <url> must be of the form
	ldap:///[<basedn>][??[<scope>][?<filter>]]

The <basedn> will default to the first suffix of the current database.
The <scope> defaults to "subtree". The default <filter> depends on which
service is being used.

If the local database is actually a proxy to a foreign LDAP server, some
mapping of schema may be needed. Some simple attribute substitutions may
be performed using

	nssov-map <service> <orig> <new>

See the nss-ldapd/README for the original attribute names used in this code.

The overlay also supports dynamic configuration in cn=config. The layout
of the config entry is

	dn: olcOverlay={0}nssov,ocDatabase={1}hdb,cn=config
	objectClass: olcOverlayConfig
	objectClass: olcNssOvConfig
	olcOverlay: {0}nssov
	olcNssSvc: passwd ldap:///ou=users,dc=example,dc=com??one
	olcNssMap: passwd uid accountName

which enables the passwd service, and uses the accountName attribute to
fetch what is usually retrieved from the uid attribute.

PAM authentication, account management, session management, and password
management are supported.

Authentication is performed using Simple Binds. Since all operations occur
inside the slapd overlay, "fake" connections are used and they are
inherently secure. Two methods of mapping the PAM username to an LDAP DN
are provided:
  the mapping can be accomplished using slapd's authz-regexp facility. In
this case, a DN of the form
	cn=<service>+uid=<user>,cn=<hostname>,cn=pam,cn=auth
is fed into the regexp matcher. If a match is produced, the resulting DN
is used.
  otherwise, the NSS passwd map is invoked (which means it must already
be configured).

If no DN is found, the overlay returns PAM_USER_UNKNOWN. If the DN is
found, and Password Policy is supported, then the Bind will use the
Password Policy control and return expiration information to PAM.

Account management also uses two methods. These methods depend on the
ldapns.schema included with the nssov source.
  The first is identical to the method used in PADL's pam_ldap module:
host and authorizedService attributes may be looked up in the user's entry,
and checked to determine access. Also a check may be performed to see if
the user is a member of a particular group. This method is pretty
inflexible and doesn't scale well to large networks of users, hosts,
and services.
  The second uses slapd's ACL engine to check if the user has "compare"
privilege on an ipHost object whose name matches the current hostname, and
whose authorizedService attribute matches the current service name. This
method is preferred, since it allows authorization to be centralized in
the ipHost entries instead of scattered across the entire user population.
The ipHost entries must have an authorizedService attribute (e.g. by way
of the authorizedServiceObject auxiliary class) to use this method.

Session management: the overlay may optionally add a "logged in" attribute
to a user's entry for successful logins, and delete the corresponding
value upon logout. The attribute value is of the form
	<generalizedTime> <host> <service> <tty> (<ruser@rhost>)

Password management: the overlay will perform a PasswordModify exop
in the server for the given user.