.lf 1 stdin
.TH SLAPD-LDAP 5 "2022/07/14" "OpenLDAP 2.5.13+dfsg-2~bpo11+1"
.\" Copyright 1998-2022 The OpenLDAP Foundation All Rights Reserved.
.\" Copying restrictions apply.  See COPYRIGHT/LICENSE.
.\" $OpenLDAP$
.SH NAME
slapd\-ldap \- LDAP backend to slapd
.SH SYNOPSIS
/etc/ldap/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.

The proxy instance of
.BR slapd (8)
must contain schema information for the attributes and objectClasses
used in filters, request DNs and request-related data in general.
It should also contain schema information for the data returned
by the proxied server.
It is the responsibility of the proxy administrator to keep the schema
of the proxy lined up with that of the proxied server.

.LP
Note: When looping back to the same instance of
.BR slapd (8), 
each connection requires a new thread; as a consequence, the
.BR slapd (8)
\fBthreads\fP parameter may need some tuning. In those cases,
one may consider using 
.BR slapd\-relay (5)
instead, which performs the relayed operation 
internally and thus reuses the same connection.

.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 
.B ldap
and
.B meta
databases.
This was required 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 \fBoff\fP, 
so its use is redundant and should be omitted.

.TP
.B uri <ldapurl>
LDAP server to use.  Multiple URIs can be set in a single
.B ldapurl
argument, resulting in the underlying library automatically 
calling 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.
Whenever the server that responds is not the first one in the list,
the list is rearranged and the responsive server is moved to the head,
so that it will be first contacted the next time a connection
needs to be created.
.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>]
.B [starttls=no|yes|critical]
.B [tls_cert=<file>]
.B [tls_key=<file>]
.B [tls_cacert=<file>]
.B [tls_cacertdir=<path>]
.B [tls_reqcert=never|allow|try|demand]
.B [tls_reqsan=never|allow|try|demand]
.B [tls_cipher_suite=<ciphers>]
.B [tls_ecname=<names>]
.B [tls_protocol_min=<major>[.<minor>]]
.B [tls_crlcheck=none|peer|all]
.RS
Allows one to define the parameters of the authentication method that is
internally used by the proxy to collect info related to access control,
and whenever an operation occurs with the identity of the rootdn
of the LDAP proxy database.
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.

There is no risk of giving away such values; they are only used to
check permissions.
The default is to use
.BR simple 
bind, with empty \fIbinddn\fP and \fIcredentials\fP,
which means that the related operations will be performed anonymously.
If not set, and if \fBidassert\-bind\fP is defined, this latter identity
is used instead.  See \fBidassert\-bind\fP for details.

The connection between the proxy database and the remote server
associated to this identity is cached regardless of the lifespan
of the client-proxy connection that first established it.

.B This identity is not implicitly used by the proxy
.B when the client connects anonymously.
The
.B idassert\-bind
feature, instead, in some cases can be crafted to implement that behavior,
which is \fIintrinsically unsafe and should be used with extreme care\fP.

The TLS settings default to the same as the main slapd TLS settings,
except for
.B tls_reqcert
which defaults to "demand", and
.B tls_reqsan
which defaults to "allow".
.RE

.TP
.B cancel {ABANDON|ignore|exop[\-discover]}
Defines how to handle operation cancellation.
By default,
.B abandon
is invoked, so the operation is abandoned immediately.
If set to
.BR ignore ,
no action is taken and any further response is ignored; this may result
in further response messages to be queued for that connection, so it is
recommended that long lasting connections are timed out either by
.I idle\-timeout
or
.IR conn\-ttl ,
so that resources eventually get released.
If set to
.BR exop ,
a
.I cancel
operation (RFC 3909) is issued, resulting in the cancellation 
of the current operation; the
.I cancel
operation waits for remote server response, so its use 
may not be recommended.
If set to
.BR exop\-discover ,
support of the
.I cancel 
extended operation is detected by reading the remote server's root DSE.

.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 conn\-pool\-max <int>
This directive defines the maximum size of the privileged connections pool.

.TP
.B conn\-ttl <time>
This directive causes a cached connection to be dropped and recreated
after a given ttl, regardless of being idle or not.

.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>
mostly 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.  This parameter differs from
the documented behavior in relation to the meaning of *, which in this
case allows anonymous rather than denies.

.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>]
.B [starttls=no|yes|critical]
.B [tls_cert=<file>]
.B [tls_key=<file>]
.B [tls_cacert=<file>]
.B [tls_cacertdir=<path>]
.B [tls_reqcert=never|allow|try|demand]
.B [tls_reqsan=never|allow|try|demand]
.B [tls_cipher_suite=<ciphers>]
.B [tls_ecname=<names>]
.B [tls_protocol_min=<version>]
.B [tls_crlcheck=none|peer|all]
.RS
Allows one to define the parameters of the authentication method that is
internally used by the proxy to authorize connections that are 
authenticated by other databases.
Direct binds are always proxied without any idassert handling.

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
.B 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 (Proxied Authorization, RFC 4370)
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.
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,[non\-]prescriptive,proxy\-authz\-[non\-]critical,dn\-{authzid|whoami}\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.

When the
.B proxy\-authz\-non\-critical
flag is used (the default), the proxyAuthz control is not marked as critical,
in violation of RFC 4370.  Use of
.B proxy\-authz\-critical
is recommended.

When the
.B dn\-authzid
flag is used, RFC 3829 LDAP Authorization Identity Controls
is used to retrieve the identity associated to the SASL identity;
when the
.B dn\-whoami
flag is used, RFC 4532 LDAP Who am I? Operation is performed
after the bind for the same purpose.

The TLS settings default to the same as the main slapd TLS settings,
except for
.B tls_reqcert
which defaults to "demand", and
.B tls_reqsan
which defaults to "allow".

The identity associated to this directive is also used for privileged
operations whenever \fBidassert\-bind\fP is defined and \fBacl\-bind\fP
is not.  See \fBacl\-bind\fP for details.

.TP
.B idassert-passthru <authz-regexp>
if defined, selects what
.I local
identities bypass the identity assertion feature.
Those identities need to be known by the remote host.
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 idle\-timeout <time>
This directive causes a cached connection to be dropped an recreated
after it has been idle for the specified time.

.TP
.B keepalive  <idle>:<probes>:<interval>
The
.B keepalive
parameter sets the values of \fIidle\fP, \fIprobes\fP, and \fIinterval\fP
used to check whether a socket is alive;
.I idle
is the number of seconds a connection needs to remain idle before TCP
starts sending keepalive probes;
.I probes
is the maximum number of keepalive probes TCP should send before dropping
the connection;
.I interval
is interval in seconds between individual keepalive probes.
Only some systems support the customization of these values;
the
.B keepalive
parameter is ignored otherwise, and system-wide settings are used.

.TP
.B tcp\-user\-timeout  <milliseconds>
If non-zero, corresponds to the
.B TCP_USER_TIMEOUT
set on the target connections, overriding the operating system setting.
Only some systems support the customization of this parameter, it is
ignored otherwise and system-wide settings are used.

.TP
.B network\-timeout <time>
Sets the network timeout value after which
.BR poll (2)/ select (2) 
following a 
.BR connect (2) 
returns in case of no activity.
The value is in seconds, and it can be specified as for
.BR idle\-timeout .

.TP
.B norefs <NO|yes>
If
.BR yes ,
do not return search reference responses.
By default, they are returned unless request is LDAPv2.

.TP
.B omit-unknown-schema <NO|yes>
If
.BR yes ,
do not return objectClasses or attributes that are not known to the local server.
The default is to return all schema elements.

.TP
.B noundeffilter <NO|yes>
If
.BR yes ,
return success instead of searching if a filter is undefined or contains
undefined portions.
By default, the search is propagated after replacing undefined portions
with
.BR (!(objectClass=*)) ,
which corresponds to the empty result set.

.TP
.B onerr {CONTINUE|stop}
This directive allows one to select the behavior in case an error is returned
by the remote server during a search.
The default, \fBcontinue\fP, consists in returning success.
If the value is set to \fBstop\fP, the error is returned to the client.

.TP
.B protocol\-version {0,2,3}
This directive indicates what protocol version must be used to contact
the remote server.
If set to 0 (the default), the proxy uses the same protocol version 
used by the client, otherwise the requested protocol is used.
The proxy returns \fIunwillingToPerform\fP if an operation that is 
incompatible with the requested protocol is attempted.

.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 quarantine <interval>,<num>[;<interval>,<num>[...]]
Turns on quarantine of URIs that returned
.IR LDAP_UNAVAILABLE ,
so that an attempt to reconnect only occurs at given intervals instead
of any time a client requests an operation.
The pattern is: retry only after at least
.I interval
seconds elapsed since last attempt, for exactly
.I num
times; then use the next pattern.
If
.I num
for the last pattern is "\fB+\fP", it retries forever; otherwise, 
no more retries occur.
The process can be restarted by resetting the \fIolcDbQuarantine\fP
attribute of the database entry in the configuration backend.

.TP
.B rebind\-as\-user {NO|yes}
If this option is given, the client's bind credentials are remembered
for rebinds, when trying to re-establish a broken connection,
or when chasing a referral, if 
.B chase\-referrals
is set to
.IR yes .

.TP
.B session\-tracking\-request {NO|yes}
Adds session tracking control for all requests.
The client's IP and hostname, and the identity associated to each request,
if known, are sent to the remote server for informational purposes.
This directive is incompatible with setting \fIprotocol\-version\fP to 2.

.TP
.B single\-conn {NO|yes}
Discards current cached connection when the client rebinds.

.TP
.B t\-f\-support {NO|yes|discover}
enable if the remote server supports absolute filters
(see \fIRFC 4526\fP for details).
If set to
.BR discover ,
support is detected by reading the remote server's root DSE.

.TP
.B timeout [<op>=]<val> [...]
This directive allows one to set per-operation timeouts.
Operations can be

\fB<op> ::= bind, add, delete, modrdn, modify, compare, search\fP

The overall duration of the \fBsearch\fP operation is controlled either
by the \fBtimelimit\fP parameter or by server-side enforced
time limits (see \fBtimelimit\fP and \fBlimits\fP in
.BR slapd.conf (5)
for details).
This \fBtimeout\fP parameter controls how long the target can be 
irresponsive before the operation is aborted.
Timeout is meaningless for the remaining operations,
\fBunbind\fP and \fBabandon\fP, which do not imply any response,
while it is not yet implemented in currently supported \fBextended\fP 
operations.
If no operation is specified, the timeout \fBval\fP affects all
supported operations.

Note: if the timelimit is exceeded, the operation is cancelled
(according to the \fBcancel\fP directive);
the protocol does not provide any means to rollback operations,
so the client will not be notified about the result of the operation,
which may eventually succeeded or not.
In case the timeout is exceeded during a bind operation, the connection
is destroyed, according to RFC4511.

Note: in some cases, this backend may issue binds prior
to other operations (e.g. to bind anonymously or with some prescribed
identity according to the \fBidassert\-bind\fP directive).
In this case, the timeout of the operation that resulted in the bind
is used.

.HP
.hy 0
.B tls {none|[try\-]start|[try\-]propagate|ldaps}
.B [starttls=no]
.B [tls_cert=<file>]
.B [tls_key=<file>]
.B [tls_cacert=<file>]
.B [tls_cacertdir=<path>]
.B [tls_reqcert=never|allow|try|demand]
.B [tls_reqsan=never|allow|try|demand]
.B [tls_cipher_suite=<ciphers>]
.B [tls_ecname=<names>]
.B [tls_crlcheck=none|peer|all]
.RS
Specify TLS settings for regular connections.

If the first parameter is not "none" then this configures the TLS
settings to be used for regular connections.
The StartTLS extended operation will be used when establishing the
connection unless the URI directive protocol scheme is \fBldaps://\fP.
In that case this keyword may only be set to "ldaps" and the StartTLS
operation will not be used.

With \fBpropagate\fP, the proxy issues the StartTLS operation only if
the original connection has a TLS layer set up.
The \fBtry\-\fP prefix instructs the proxy to continue operations
if the StartTLS operation failed; its use is \fBnot\fP recommended.

The TLS settings default to the same as the main slapd TLS settings,
except for
.B tls_reqcert
which defaults to "demand",
.B tls_reqsan
which defaults to "allow", and
.B starttls
which is overshadowed by the first keyword and thus ignored.
.RE

.TP
.B use\-temporary\-conn {NO|yes}
when set to 
.BR yes ,
create a temporary connection whenever competing with other threads
for a shared one; otherwise, wait until the shared connection is available.

.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
/etc/ldap/slapd.conf
default slapd configuration file
.SH SEE ALSO
.BR slapd.conf (5),
.BR slapd\-config (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