slapd-ldap — LDAP backend to slapd
ETCDIR/slapd.conf
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.
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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 |
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 every ldap
and
meta
database. This
is 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,
because the lastmod directive will be deprecated in the
future.
LDAP server to use. Multiple URIs can be set in 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.
acl-bind
bindmethod=simple|sasl
[binddn=<simple DN>] [credentials=<simple
password>] [saslmech=<SASL mech>]
[secprops=<properties>]
[realm=<realm>] [authcId=<authentication ID>]
[authzId=<authorization ID>]
Allows to define the parameters of the authentication method that is internally used by the proxy to collect info related to access control. 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.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 obsoletesacl-authcDN
, andacl-passwd
.
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.
This directive causes a cached connection to be dropped an recreated after a given ttl, regardless of being idle or not.
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>]
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 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 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 theauthzDN
orauthzID
parameters). Otherwise, the defaultproxyauthz
is used, i.e. the proxyAuthz control 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 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 theauthcDN
or a SASL bind as theauthcID
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 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
'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,{prescriptive|non-prescriptive}
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.This directive obsoletes
idassert-authcDN
,idassert-passwd
,idassert-mode
, andidassert-method
.
This directive causes a cached connection to be dropped an recreated after it has been idle for the specified 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
.
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.
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.
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.
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.
This directive allows to set per-operation timeouts.
If no operation is specified, it affects all.
Currently, only write operations are addressed, because
searches can already be limited by means of the
limits
directive (see slapd.conf(5) for
details), and other operations are not supposed to
incur into the need for timeouts. Note: if the
timelimit is exceeded, the operation is abandoned; the
protocol does not provide any means to rollback the
operation, so the client will not know if the operation
eventually succeeded or not.
execute the StartTLS extended operation when the
connection is initialized; only works if the URI
directive protocol scheme is not ldaps://
. 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 highly
deprecated.
The LDAP backend has been heavily reworked between releases 2.2 and 2.3; 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.
this directive is no longer supported. Use the
uri
directive
as described above.
DN which 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. See the idassert-*
feature
instead. This directive is obsoleted by the binddn
arg of
acl-bind
when
bindmethod
=simple
, and will be
dismissed in the future.
Password used with the above acl-authcDN
directive.
This directive is obsoleted by the binddn
arg of
acl-bind
when
bindmethod
=simple
, and will be
dismissed in the future.
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.
Password used with the idassert-authcDN
above.
This directive is obsoleted by the crendentials
of
idassert-bind
when bindmethod
=simple
, and will be
dismissed in the future.
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.
This directive is obsoleted by the bindmethod
arg of
idassert-bind
, and will
be dismissed in the future.
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.
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.
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.
slapd.conf(5), slapd−meta(5), slapo−chain(5), slapo−pcache(5), slapo−rwm(5), slapo−translucent(5), slapd(8), ldap(3).