Section (5) slapd-ldap
Name
slapd−ldap — LDAP backend to slapd
Synopsis
ETCDIR/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_zsingle_quotesz_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.
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Note |
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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 |
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.
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Note |
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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 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
simple
bind, with emptybinddn
andcredentials
, which means that the related operations will be performed anonymously. If not set, and ifidassert−bind
is defined, this latter identity is used instead. Seeidassert−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 obsoletesacl−authcDN
, andacl−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 toignore
, 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 byidle−timeout
orconn−ttl
, so that resources eventually get released. If set toexop
, acancel
operation (RFC 3909) is issued, resulting in the cancellation of the current operation; thecancel
operation waits for remote server response, so its use may not be recommended. If set toexop−discover
, support of thecancel
extended operation is detected by reading the remote server_zsingle_quotesz_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 theauthzFrom
attribute. See slapd.conf(5), section related toauthz−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 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
proxyAuthz
privileges on a wide set of DNs, e.g.authzTo=dn.subtree:
, and the remote server to haveauthz−policy
set toto
orboth
. See slapd.conf(5) for details on these statements and for remarks and drawbacks about their usage. The supported bindmethods arenone|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 theauthzDN
orauthzID
parameters). Otherwise, the defaultproxyauthz
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, andauthzId
is given, the proxy always authorizes that identity. <authorization ID> can beu:<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 theauthcDN
or a SASL bind as theauthcID
and assert the client_zsingle_quotesz_s identity when it is not anonymous. The other modes imply that the proxy will always either perform a simple bind as theauthcDN
or a SASL bind as theauthcID
, unless restricted byidassert−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 areanonymous
andself
, which respectively mean that theempty
or theclient
_zsingle_quotesz_s identity will be asserted;none
, which means that no proxyAuthz control will be used, so theauthcDN
or theauthcID
identity will be asserted. For all modes that require the use of theproxyAuthz
control, on the remote server the proxy identity must have appropriateauthzTo
permissions, or the asserted identities must have appropriateauthzFrom
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 withinappropriateAuthentication
for those identities whose assertion is not allowed by theidassert−authzFrom
patterns. If thenon−prescriptive
flag is used, operations are performed anonymously for those identities whose assertion is not allowed by theidassert−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 ofproxy−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 andacl−bind
is not. Seeacl−bind
for details.This directive obsoletes
idassert−authcDN
,idassert−passwd
,idassert−mode
, andidassert−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 theauthzFrom
attribute. See slapd.conf(5), section related toauthz−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 ofidle
,probes
, andinterval
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; thekeepalive
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. - mit-unknown-schema <NO|yes>
-
If
yes
, do not return objectClasses or attributes that are not known to the local server. The default is to return all schema elements. - 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. - nerr {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,
continue
, consists in returning success. If the value is set tostop
, 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_zsingle_quotesz_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 exactlynum
times; then use the next pattern. Ifnum
for the last pattern is+
, it retries forever; otherwise, no more retries occur. The process can be restarted by resetting theolcDbQuarantine
attribute of the database entry in the configuration backend. - rebind−as−user {NO|yes}
-
If this option is given, the client_zsingle_quotesz_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 toyes
. - session−tracking−request {NO|yes}
-
Adds session tracking control for all requests. The client_zsingle_quotesz_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_zsingle_quotesz_s root DSE. - timeout [<op>=]<val> [...]
-
This directive allows one 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 thetimelimit
parameter or by server-side enforced time limits (seetimelimit
andlimits
in slapd.conf(5) for details). Thistimeout
parameter controls how long the target can be irresponsive before the operation is aborted. Timeout is meaningless for the remaining operations,unbind
andabandon
, which do not imply any response, while it is not yet implemented in currently supportedextended
operations. If no operation is specified, the timeoutval
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}
[starttls=no]
[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. Thetry−
prefix instructs the proxy to continue operations if the StartTLS operation failed; its use isnot
recommended.The TLS settings default to the same as the main slapd TLS settings, except for
tls_reqcert
which defaults to demand andstarttls
which is overshadowed by the first keyword and thus ignored. - 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 ofacl−bind
whenbindmethod
=simple
, and will be dismissed in the future. - acl−passwd <password>
-
Formerly known as the
bindpw
, it is the password used with the aboveacl−authcDN
directive. This directive is obsoleted by thecredentials
arg ofacl−bind
whenbindmethod
=simple
, and will be dismissed in the future. - idassert−authcDN <administrative DN for proxyAuthz purposes>
-
DN which is used to propagate the client_zsingle_quotesz_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 ofidassert−bind
whenbindmethod
=simple
, and will be dismissed in the future. - idassert−passwd <password>
-
Password used with the
idassert−authcDN
above. This directive is obsoleted by thecrendentials
arg ofidassert−bind
whenbindmethod
=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 ofidassert−bind
, and will be dismissed in the future. - idassert−method <method> [<saslargs>]
-
This directive is obsoleted by the
bindmethod
arg ofidassert−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 statementoverlay 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.