openldap/doc/man/man5/slapd-ldap.5

.TH SLAPD-LDAP 5 "RELEASEDATE" "OpenLDAP LDVERSION"
.\" Copyright 1998-2005 The OpenLDAP Foundation All Rights Reserved.
.\" Copying restrictions apply.  See COPYRIGHT/LICENSE.
.\" $OpenLDAP$
.SH NAME
slapd-ldap \- LDAP backend to slapd
.SH SYNOPSIS
ETCDIR/slapd.conf
.SH DESCRIPTION
The LDAP backend to
.BR slapd (8)
is not an actual database; instead it acts as a proxy to forward incoming
requests to another LDAP server. While processing requests it will also
chase referrals, so that referrals are fully processed instead of being
returned to the slapd client.

Sessions that explicitly Bind to the back-ldap database always create their
own private connection to the remote LDAP server. Anonymous sessions will
share a single anonymous connection to the remote server. For sessions bound
through other mechanisms, all sessions with the same DN will share the
same connection. This connection pooling strategy can enhance the proxy's
efficiency by reducing the overhead of repeatedly making/breaking multiple
connections.

The ldap database can also act as an information service, i.e. the identity
of locally authenticated clients is asserted to the remote server, possibly
in some modified form.
For this purpose, the proxy binds to the remote server with some 
administrative identity, and, if required, authorizes the asserted identity.
See the 
.IR idassert- *
rules below.
The administrative identity of the proxy, on the remote server, must be 
allowed to authorize by means of appropriate
.B authzTo
rules; see 
.BR slapd.conf (5)
for details.

.SH CONFIGURATION
These
.B slapd.conf
options apply to the LDAP backend database.
That is, they must follow a "database ldap" line and come before any
subsequent "backend" or "database" lines.
Other database options are described in the
.BR slapd.conf (5)
manual page.
.LP
Note: In early versions of back-ldap it was recommended to always set
.LP
.RS
.nf
lastmod  off
.fi
.RE
.LP
for every
.B ldap
and
.B meta
database.
This is because operational attributes related to entry creation and
modification should not be proxied, as they could be mistakenly written
to the target server(s), generating an error.
The current implementation automatically sets lastmod to off, so its use
is redundant and should be omitted, because the lastmod directive will
be deprecated in the future.

.TP
.B uri <ldapurl>
LDAP server to use.  Multiple URIs can be set in in a single
.B ldapurl
argument, resulting in the underlying library automatically 
call the first server of the list that responds, e.g. 

\fBuri "ldap://host/ ldap://backup-host"\fP

The URI list is space- or comma-separated.
This statement is mandatory.
.\".TP
.\".B server <hostport>
.\"Obsolete option; same as `uri ldap://<hostport>/'.
.HP
.hy 0
.B acl-bind
.B bindmethod=simple|sasl [binddn=<simple DN>] [credentials=<simple password>]
.B [saslmech=<SASL mech>] [secprops=<properties>] [realm=<realm>]
.B [authcId=<authentication ID>] [authzId=<authorization ID>]
.RS
Allows to define the parameters of the authentication method that is 
internally used by the proxy to collect info related to access control.
The identity defined by this directive, according to the properties
associated to the authentication method, is supposed to have read access 
on the target server to attributes used on the proxy for ACL checking.
The
.B secprops
field is currently ignored.
There is no risk of giving away such values; they are only used to
check permissions.
The default is to use
.BR simple ,
with empty binddn and credentials,
which means that the related operations will be performed anonymously.

.B This identity is by no means implicitly used by the proxy 
.B when the client connects anonymously.
See the
.B idassert-bind
feature instead.
This directive obsoletes
.BR acl-authcDN ,
and
.BR acl-passwd .
.RE

.HP
.hy 0
.B idassert-bind
.B bindmethod=none|simple|sasl [binddn=<simple DN>] [credentials=<simple password>]
.B [saslmech=<SASL mech>] [secprops=<properties>] [realm=<realm>]
.B [authcId=<authentication ID>] [authzId=<authorization ID>]
.B [authz={native|proxyauthz}] [mode=<mode>] [flags=<flags>]
.RS
Allows to define the parameters of the authentication method that is 
internally used by the proxy to authorize connections that are 
authenticated by other databases.
The identity defined by this directive, according to the properties
associated to the authentication method, is supposed to have auth access 
on the target server to attributes used on the proxy for authentication
and authorization, and to be allowed to authorize the users.
This requires to have
.B proxyAuthz
privileges on a wide set of DNs, e.g.
.BR authzTo=dn.subtree:"" ,
and the remote server to have
.B authz-policy
set to
.B to
or
.BR both .
See
.BR slapd.conf (5)
for details on these statements and for remarks and drawbacks about
their usage.
The supported bindmethods are

\fBnone|simple|sasl\fP

where
.B none
is the default, i.e. no \fIidentity assertion\fP is performed.

The authz parameter is used to instruct the SASL bind to exploit 
.B native 
SASL authorization, if available; since connections are cached,
this should only be used when authorizing with a fixed identity
(e.g. by means of the 
.B authzDN
or
.B authzID
parameters).
Otherwise, the default
.B proxyauthz
is used, i.e. the proxyAuthz control is added to all operations.

The supported modes are:

\fB<mode> := {legacy|anonymous|none|self}\fP

If 
.B <mode>
is not present, and 
.B authzId
is given, the proxy always authorizes that identity.
.B <authorization ID>
can be 

\fBu:<user>\fP

\fB[dn:]<DN>\fP

The former is supposed to be expanded by the remote server according 
to the authz rules; see
.BR slapd.conf (5)
for details.
In the latter case, whether or not the 
.B dn:
prefix is present, the string must pass DN validation and normalization.

The default mode is 
.BR legacy ,
which implies that the proxy will either perform a simple bind as the
.I authcDN
or a SASL bind as the
.I authcID
and assert the client's identity when it is not anonymous.
Direct binds are always proxied.
The other modes imply that the proxy will always either perform a simple bind 
as the
.IR authcDN
or a SASL bind as the
.IR authcID ,
unless restricted by
.BR idassert-authzFrom
rules (see below), in which case the operation will fail;
eventually, it will assert some other identity according to
.BR <mode> .
Other identity assertion modes are
.BR anonymous
and
.BR self ,
which respectively mean that the 
.I empty 
or the 
.IR client 's 
identity
will be asserted;
.BR none ,
which means that no proxyAuthz control will be used, so the
.I authcDN
or the
.I authcID
identity will be asserted.
For all modes that require the use of the
.I proxyAuthz 
control, on the remote server the proxy identity must have appropriate 
.I authzTo
permissions, or the asserted identities must have appropriate
.I authzFrom 
permissions.  Note, however, that the ID assertion feature is mostly 
useful when the asserted identities do not exist on the remote server.

Flags can be

\fBoverride,{prescriptive|non-prescriptive}\fP

When the 
.B override
flag is used, identity assertion takes place even when the database
is authorizing for the identity of the client, i.e. after binding
with the provided identity, and thus authenticating it, the proxy
performs the identity assertion using the configured identity and
authentication method.

When the
.B prescriptive
flag is used (the default), operations fail with
\fIinappropriateAuthentication\fP
for those identities whose assertion is not allowed by the
.B idassert-authzFrom
patterns.
If the 
.B non-prescriptive
flag is used, operations are performed anonymously for those identities 
whose assertion is not allowed by the
.B idassert-authzFrom
patterns.

This directive obsoletes
.BR idassert-authcDN ,
.BR idassert-passwd ,
.BR idassert-mode ,
and
.BR idassert-method .
.RE

.TP
.B idassert-authzFrom <authz-regexp>
if defined, selects what
.I local
identities are authorized to exploit the identity assertion feature.
The string
.B <authz-regexp>
follows the rules defined for the
.I authzFrom
attribute.
See 
.BR slapd.conf (5),
section related to
.BR authz-policy ,
for details on the syntax of this field.

.TP
.B proxy-whoami {NO|yes}
Turns on proxying of the WhoAmI extended operation. If this option is
given, back-ldap will replace slapd's original WhoAmI routine with its
own. On slapd sessions that were authenticated by back-ldap, the WhoAmI
request will be forwarded to the remote LDAP server. Other sessions will
be handled by the local slapd, as before. This option is mainly useful
in conjunction with Proxy Authorization.

.TP
.B rebind-as-user {NO|yes}
If this option is given, the client's bind credentials are remembered
for rebinds when chasing referrals.  Useful when
\fBchase-referrals\fP is set to \fByes\fP, useless otherwise.

.TP
.B chase-referrals {YES|no}
enable/disable automatic referral chasing, which is delegated to the
underlying libldap, with rebinding eventually performed if the
\fBrebind-as-user\fP directive is used.  The default is to chase referrals.

.TP
.B tls {[try-]start|[try-]propagate}
execute the start TLS extended operation when the connection is initialized;
only works if the URI directive protocol scheme is not \fBldaps://\fP.
\fBpropagate\fP issues the Start TLS exop only if the original
connection did.
The \fBtry-\fP prefix instructs the proxy to continue operations
if start TLS failed; its use is highly deprecated.

.TP
.B t-f-support {NO|yes|discover}
enable if the remote server supports absolute filters
(see \fIdraft-zeilenga-ldap-t-f\fP for details).
If set to
.BR discover ,
support is detected by reading the remote server's root DSE.

.TP
.B timeout [{add|delete|modify|modrdn}=]<val> [...]
This directive allows to set per-operation timeouts.
If no operation is specified, it affects all.
Currently, only write operations are addressed, because searches
can already be limited by means of the
.B limits
directive (see 
.BR slapd.conf (5)
for details), and other operations are not supposed to incur into the
need for timeouts.
Note: if the timelimit is exceeded, the operation is abandoned;
the protocol does not provide any means to rollback the operation,
so the client will not know if the operation eventually succeeded or not.

.SH BACKWARD COMPATIBILITY
The LDAP backend has been heavily reworked between releases 2.2 and 2.3;
as a side-effect, some of the traditional directives have been
deprecated and should be no longer used.

.TP
.B server <hostname[:port]>
this directive is no longer supported.  Use the 
.B uri
directive as described above.

.TP
.B acl-authcDN "<administrative DN for access control purposes>"
DN which is used to query the target server for acl checking; it
is supposed to have read access on the target server to attributes used
on the proxy for acl checking.
There is no risk of giving away such values; they are only used to
check permissions.
.B The acl-authcDN identity is by no means implicitly used by the proxy 
.B when the client connects anonymously.
See the
.B idassert-*
feature instead.
This directive is obsoleted by
.BR acl-bind ,
and may dismissed in the future.

.TP
.B acl-passwd <password>
Password used with the
.B 
acl-authcDN
above.
This directive is obsoleted by
.BR acl-bind ,
and may be dismissed in the future.

.TP
.B idassert-authcDN "<administrative DN for proxyAuthz purposes>"
DN which is used to propagate the client's identity to the target
by means of the proxyAuthz control when the client does not
belong to the DIT fragment that is being proxied by back-ldap.
This directive is obsoleted by
.BR idassert-bind ,
and may be dismissed in the future.

.TP
.B idassert-passwd <password>
Password used with the
.B idassert-authcDN
above.
This directive is obsoleted by
.BR idassert-bind ,
and may be dismissed in the future.

.TP
.B idassert-mode <mode> [<flags>]
defines what type of
.I identity assertion
is used.
This directive is obsoleted by
.BR idassert-bind ,
and may be dismissed in the future.

.TP
.B idassert-method <method> [<saslargs>]
This directive is obsoleted by
.BR idassert-bind ,
and may be dismissed in the future.

.TP
.B suffixmassage, map, rewrite*
These directives are no longer supported by back-ldap; their 
functionality is now delegated to the
.B rwm
overlay.  Essentially, add a statement

.B overlay rwm

first, and prefix all rewrite/map statements with
.B rwm-
to obtain the original behavior.
See
.BR slapo-rwm (5)
for details.
.\" However, to ease update from existing configurations, back-ldap still 
.\" recognizes them and automatically instantiates the
.\" .B rwm
.\" overlay if available and not instantiated yet.
.\" This behavior may change in the future.

.SH ACCESS CONTROL
The
.B ldap
backend does not honor all ACL semantics as described in
.BR slapd.access (5).
In general, access checking is delegated to the remote server(s).
Only
.B read (=r)
access to the
.B entry
pseudo-attribute and to the other attribute values of the entries
returned by the
.B search
operation is honored, which is performed by the frontend.

.SH OVERLAYS
The LDAP backend provides basic proxying functionalities to many overlays.
The 
.B chain
overlay, described in
.BR slapo\-chain (5),
and the
.B translucent
overlay, described in
.BR slapo\-translucent (5),
deserve a special mention.

Conversely, there are many overlays that are best used in conjunction
with the LDAP backend.
The
.B proxycache 
overlay allows caching of LDAP search requests (queries) 
in a local database.
See 
.BR slapo\-pcache (5)
for details.
The
.B rwm
overlay provides DN rewrite and attribute/objectClass mapping
capabilities to the underlying database.
See 
.BR slapo\-rwm (5)
for details.

.SH FILES
.TP
ETCDIR/slapd.conf
default slapd configuration file
.SH SEE ALSO
.BR slapd.conf (5),
.BR slapd\-meta (5),
.BR slapo\-chain (5),
.BR slapo\-pcache (5),
.BR slapo\-rwm (5),
.BR slapo\-translucent (5),
.BR slapd (8),
.BR ldap (3).
.SH AUTHOR
Howard Chu, with enhancements by Pierangelo Masarati