Provided by: slapd_2.4.42+dfsg-2ubuntu3.13_amd64 
NAME
slapd-ldap - LDAP backend to slapd
SYNOPSIS
/etc/ldap/slapd.conf
DESCRIPTION
The LDAP backend to 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 idassert-* rules below. The
administrative identity of the proxy, on the remote server, must be allowed to authorize
by means of appropriate authzTo rules; see slapd.conf(5) for details.
The proxy instance of 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.
Note: When looping back to the same instance of slapd(8), each connection requires a new
thread; as a consequence, slapd(8) must be compiled with thread support, and the threads
parameter may need some tuning; in those cases, one may consider using slapd-relay(5)
instead, which performs the relayed operation internally and thus reuses the same
connection.
CONFIGURATION
These 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 slapd.conf(5) manual page.
Note: In early versions of back-ldap it was recommended to always set
lastmod off
for ldap and 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 off, so its use is redundant and should be omitted.
uri <ldapurl>
LDAP server to use. Multiple URIs can be set in a single ldapurl argument,
resulting in the underlying library automatically calling the first server of the
list that responds, e.g.
uri "ldap://host/ ldap://backup-host/"
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.
acl-bind bindmethod=simple|sasl [binddn=<simple DN>] [credentials=<simple password>]
[saslmech=<SASL mech>] [secprops=<properties>] [realm=<realm>]
[authcId=<authentication ID>] [authzId=<authorization ID>]
[starttls=no|yes|critical] [tls_cert=<file>] [tls_key=<file>] [tls_cacert=<file>]
[tls_cacertdir=<path>] [tls_reqcert=never|allow|try|demand]
[tls_cipher_suite=<ciphers>] [tls_protocol_min=<major>[.<minor>]]
[tls_crlcheck=none|peer|all]
Allows 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 simple bind, with empty binddn and credentials,
which means that the related operations will be performed anonymously. If not set,
and if idassert-bind is defined, this latter identity is used instead. See
idassert-bind 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.
This identity is not implicitly used by the proxy when the client connects
anonymously. The idassert-bind feature, instead, in some cases can be crafted to
implement that behavior, which is intrinsically unsafe and should be used with
extreme care. This directive obsoletes acl-authcDN, and acl-passwd.
The TLS settings default to the same as the main slapd TLS settings, except for
tls_reqcert which defaults to "demand".
cancel {ABANDON|ignore|exop[-discover]}
Defines how to handle operation cancellation. By default, abandon is invoked, so
the operation is abandoned immediately. If set to 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 idle-timeout or conn-ttl, so that resources eventually get
released. If set to exop, a cancel operation (RFC 3909) is issued, resulting in
the cancellation of the current operation; the cancel operation waits for remote
server response, so its use may not be recommended. If set to exop-discover,
support of the cancel extended operation is detected by reading the remote server's
root DSE.
chase-referrals {YES|no}
enable/disable automatic referral chasing, which is delegated to the underlying
libldap, with rebinding eventually performed if the rebind-as-user directive is
used. The default is to chase referrals.
conn-ttl <time>
This directive causes a cached connection to be dropped and recreated after a given
ttl, regardless of being idle or not.
idassert-authzFrom <authz-regexp>
if defined, selects what local identities are authorized to exploit the identity
assertion feature. The string <authz-regexp> follows the rules defined for the
authzFrom attribute. See slapd.conf(5), section related to authz-policy, for
details on the syntax of this field.
idassert-bind bindmethod=none|simple|sasl [binddn=<simple DN>] [credentials=<simple
password>] [saslmech=<SASL mech>] [secprops=<properties>] [realm=<realm>]
[authcId=<authentication ID>] [authzId=<authorization ID>]
[authz={native|proxyauthz}] [mode=<mode>] [flags=<flags>]
[starttls=no|yes|critical] [tls_cert=<file>] [tls_key=<file>] [tls_cacert=<file>]
[tls_cacertdir=<path>] [tls_reqcert=never|allow|try|demand]
[tls_cipher_suite=<ciphers>] [tls_protocol_min=<version>]
[tls_crlcheck=none|peer|all]
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. 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 proxyAuthz privileges on a
wide set of DNs, e.g. authzTo=dn.subtree:"", and the remote server to have
authz-policy set to to or both. See slapd.conf(5) for details on these statements
and for remarks and drawbacks about their usage. The supported bindmethods are
none|simple|sasl
where none is the default, i.e. no identity assertion is performed.
The authz parameter is used to instruct the SASL bind to exploit 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 authzDN or authzID
parameters). Otherwise, the default proxyauthz is used, i.e. the proxyAuthz
control (Proxied Authorization, RFC 4370) is added to all operations.
The supported modes are:
<mode> := {legacy|anonymous|none|self}
If <mode> is not present, and authzId is given, the proxy always authorizes that
identity. <authorization ID> can be
u:<user>
[dn:]<DN>
The former is supposed to be expanded by the remote server according to the authz
rules; see slapd.conf(5) for details. In the latter case, whether or not the dn:
prefix is present, the string must pass DN validation and normalization.
The default mode is legacy, which implies that the proxy will either perform a
simple bind as the authcDN or a SASL bind as the 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 authcDN or a SASL bind as the authcID,
unless restricted by idassert-authzFrom rules (see below), in which case the
operation will fail; eventually, it will assert some other identity according to
<mode>. Other identity assertion modes are anonymous and self, which respectively
mean that the empty or the client's identity will be asserted; none, which means
that no proxyAuthz control will be used, so the authcDN or the authcID identity
will be asserted. For all modes that require the use of the proxyAuthz control, on
the remote server the proxy identity must have appropriate authzTo permissions, or
the asserted identities must have appropriate 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
override,[non-]prescriptive,proxy-authz-[non-]critical
When the 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 prescriptive flag is used (the default), operations fail with
inappropriateAuthentication for those identities whose assertion is not allowed by
the idassert-authzFrom patterns. If the non-prescriptive flag is used, operations
are performed anonymously for those identities whose assertion is not allowed by
the idassert-authzFrom patterns.
When the proxy-authz-non-critical flag is used (the default), the proxyAuthz
control is not marked as critical, in violation of RFC 4370. Use of
proxy-authz-critical is recommended.
The TLS settings default to the same as the main slapd TLS settings, except for
tls_reqcert which defaults to "demand".
The identity associated to this directive is also used for privileged operations
whenever idassert-bind is defined and acl-bind is not. See acl-bind for details.
This directive obsoletes idassert-authcDN, idassert-passwd, idassert-mode, and
idassert-method.
idassert-passthru <authz-regexp>
if defined, selects what local identities bypass the identity assertion feature.
Those identities need to be known by the remote host. The string <authz-regexp>
follows the rules defined for the authzFrom attribute. See slapd.conf(5), section
related to authz-policy, for details on the syntax of this field.
idle-timeout <time>
This directive causes a cached connection to be dropped an recreated after it has
been idle for the specified time.
keepalive <idle>:<probes>:<interval>
The keepalive parameter sets the values of idle, probes, and interval used to check
whether a socket is alive; idle is the number of seconds a connection needs to
remain idle before TCP starts sending keepalive probes; probes is the maximum
number of keepalive probes TCP should send before dropping the connection; interval
is interval in seconds between individual keepalive probes. Only some systems
support the customization of these values; the keepalive parameter is ignored
otherwise, and system-wide settings are used.
network-timeout <time>
Sets the network timeout value after which poll(2)/select(2) following a connect(2)
returns in case of no activity. The value is in seconds, and it can be specified
as for idle-timeout.
norefs <NO|yes>
If yes, do not return search reference responses. By default, they are returned
unless request is LDAPv2.
noundeffilter <NO|yes>
If 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 (!(objectClass=*)), which corresponds to the empty result set.
onerr {CONTINUE|stop}
This directive allows to select the behavior in case an error is returned by the
remote server during a search. The default, continue, consists in returning
success. If the value is set to stop, the error is returned to the client.
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
unwillingToPerform if an operation that is incompatible with the requested protocol
is attempted.
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.
quarantine <interval>,<num>[;<interval>,<num>[...]]
Turns on quarantine of URIs that returned 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 interval seconds elapsed
since last attempt, for exactly num times; then use the next pattern. If num for
the last pattern is "+", it retries forever; otherwise, no more retries occur. The
process can be restarted by resetting the olcDbQuarantine attribute of the database
entry in the configuration backend.
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
chase-referrals is set to yes.
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
protocol-version to 2.
single-conn {NO|yes}
Discards current cached connection when the client rebinds.
t-f-support {NO|yes|discover}
enable if the remote server supports absolute filters (see RFC 4526 for details).
If set to discover, support is detected by reading the remote server's root DSE.
timeout [<op>=]<val> [...]
This directive allows to set per-operation timeouts. Operations can be
<op> ::= bind, add, delete, modrdn, modify, compare, search
The overall duration of the search operation is controlled either by the timelimit
parameter or by server-side enforced time limits (see timelimit and limits in
slapd.conf(5) for details). This timeout parameter controls how long the target
can be irresponsive before the operation is aborted. Timeout is meaningless for
the remaining operations, unbind and abandon, which do not imply any response,
while it is not yet implemented in currently supported extended operations. If no
operation is specified, the timeout val affects all supported operations.
Note: if the timelimit is exceeded, the operation is cancelled (according to the
cancel 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 idassert-bind
directive). In this case, the timeout of the operation that resulted in the bind
is used.
tls {[try-]start|[try-]propagate|ldaps} [tls_cert=<file>] [tls_key=<file>]
[tls_cacert=<file>] [tls_cacertdir=<path>] [tls_reqcert=never|allow|try|demand]
[tls_cipher_suite=<ciphers>] [tls_crlcheck=none|peer|all]
Specify the use of TLS when a regular connection is initialized. The StartTLS
extended operation will be used unless the URI directive protocol scheme is
ldaps://. In that case this keyword may only be set to "ldaps" and the StartTLS
operation will not be used. propagate issues the StartTLS operation only if the
original connection did. The try- prefix instructs the proxy to continue
operations if the StartTLS operation failed; its use is not recommended.
The TLS settings default to the same as the main slapd TLS settings, except for
tls_reqcert which defaults to "demand".
use-temporary-conn {NO|yes}
when set to yes, create a temporary connection whenever competing with other
threads for a shared one; otherwise, wait until the shared connection is available.
BACKWARD COMPATIBILITY
The LDAP backend has been heavily reworked between releases 2.2 and 2.3, and subsequently
between 2.3 and 2.4. As a side-effect, some of the traditional directives have been
deprecated and should be no longer used, as they might disappear in future releases.
acl-authcDN <administrative DN for access control purposes>
Formerly known as the binddn, it is the DN that 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.
The acl-authcDN identity is by no means implicitly used by the proxy when the
client connects anonymously. The idassert-* feature can be used (at own risk) for
that purpose instead.
This directive is obsoleted by the binddn arg of acl-bind when bindmethod=simple,
and will be dismissed in the future.
acl-passwd <password>
Formerly known as the bindpw, it is the password used with the above acl-authcDN
directive. This directive is obsoleted by the credentials arg of acl-bind when
bindmethod=simple, and will be dismissed in the future.
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 the binddn arg of
idassert-bind when bindmethod=simple, and will be dismissed in the future.
idassert-passwd <password>
Password used with the idassert-authcDN above. This directive is obsoleted by the
crendentials arg of idassert-bind when bindmethod=simple, and will be dismissed in
the future.
idassert-mode <mode> [<flags>]
defines what type of identity assertion is used. This directive is obsoleted by
the mode arg of idassert-bind, and will be dismissed in the future.
idassert-method <method> [<saslargs>]
This directive is obsoleted by the bindmethod arg of idassert-bind, and will be
dismissed in the future.
port <port>
this directive is no longer supported. Use the uri directive as described above.
server <hostname[:port]>
this directive is no longer supported. Use the uri directive as described above.
suffixmassage, map, rewrite*
These directives are no longer supported by back-ldap; their functionality is now
delegated to the rwm overlay. Essentially, add a statement
overlay rwm
first, and prefix all rewrite/map statements with rwm- to obtain the original
behavior. See slapo-rwm(5) for details.
ACCESS CONTROL
The ldap backend does not honor all ACL semantics as described in slapd.access(5). In
general, access checking is delegated to the remote server(s). Only read (=r) access to
the entry pseudo-attribute and to the other attribute values of the entries returned by
the search operation is honored, which is performed by the frontend.
OVERLAYS
The LDAP backend provides basic proxying functionalities to many overlays. The chain
overlay, described in slapo-chain(5), and the translucent overlay, described in
slapo-translucent(5), deserve a special mention.
Conversely, there are many overlays that are best used in conjunction with the LDAP
backend. The proxycache overlay allows caching of LDAP search requests (queries) in a
local database. See slapo-pcache(5) for details. The rwm overlay provides DN rewrite and
attribute/objectClass mapping capabilities to the underlying database. See slapo-rwm(5)
for details.
FILES
/etc/ldap/slapd.conf
default slapd configuration file
SEE ALSO
slapd.conf(5), slapd-config(5), slapd-meta(5), slapo-chain(5), slapo-pcache(5),
slapo-rwm(5), slapo-translucent(5), slapd(8), ldap(3).
AUTHOR
Howard Chu, with enhancements by Pierangelo Masarati