slapd-ldap(5) — Linux manual pages

Linux manual pages	Section 5

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 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 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 rearranged and the responsive server is moved to the head, so that it will be first contacted the next time a connection needs 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_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

ETCDIR/slapd.conf: default slapd configuration file

AUTHOR

Howard Chu, with enhancements by Pierangelo Masarati

See the following documents: COPYRIGHT, LICENSE

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