SLAPD-LDAP(5) File Formats Manual SLAPD-LDAP(5)
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 DN and
request-related data in general. It should also contain schema information for the data returned by the proxied server. It is the respon-
sibility 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 com-
piled 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 subse-
quent "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 call
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 rear-
ranged and the responsive server is moved to the head, so that it will be first contacted the next time a connection needs be cre-
ated.
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_ciphersuite=<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 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 by no means 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 an 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_ciphersuite=<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. 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. Direct binds are always proxied. 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.
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.
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 draft-zeilenga-ldap-t-f 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_ciphersuite=<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
OpenLDAP 2012/04/23 SLAPD-LDAP(5)