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 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
/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