Provided by: slapd_2.5.13+dfsg-1ubuntu1_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, the slapd(8) 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_reqsan=never|allow|try|demand] [tls_cipher_suite=<ciphers>]
[tls_ecname=<names>] [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 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.
The TLS settings default to the same as the main slapd TLS settings, except for
tls_reqcert which defaults to "demand", and tls_reqsan which defaults to "allow".
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-pool-max <int>
This directive defines the maximum size of the privileged connections pool.
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> mostly 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. This parameter differs from the documented
behavior in relation to the meaning of *, which in this case allows anonymous
rather than denies.
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_reqsan=never|allow|try|demand] [tls_cipher_suite=<ciphers>]
[tls_ecname=<names>] [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 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,dn-{authzid|whoami}
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.
When the dn-authzid flag is used, RFC 3829 LDAP Authorization Identity Controls is
used to retrieve the identity associated to the SASL identity; when the dn-whoami
flag is used, RFC 4532 LDAP Who am I? Operation is performed after the bind for the
same purpose.
The TLS settings default to the same as the main slapd TLS settings, except for
tls_reqcert which defaults to "demand", and tls_reqsan which defaults to "allow".
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.
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.
tcp-user-timeout <milliseconds>
If non-zero, corresponds to the TCP_USER_TIMEOUT set on the target
connections, overriding the operating system setting. Only some systems
support the customization of this parameter, it 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.
omit-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.
onerr {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 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 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 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 {none|[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_reqsan=never|allow|try|demand]
[tls_cipher_suite=<ciphers>] [tls_ecname=<names>]
[tls_crlcheck=none|peer|all]
Specify TLS settings for regular connections.
If the first parameter is not "none" then this configures the TLS settings
to be used for regular connections. The StartTLS extended operation will be
used when establishing the connection 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.
With propagate, the proxy issues the StartTLS operation only if the original
connection has a TLS layer set up. 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", tls_reqsan which defaults to
"allow", and starttls 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.
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