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SLAPD-LDAP(5)
NAME
slapd-ldap - LDAP backend to slapd
SYNOPSIS
/usr/internet/openldap/etc/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.
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 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.
uri <ldapurl>
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 empty binddn and credentials, which means that the related
operations will be performed anonymously.
This identity is by no means 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.
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>]
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 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,{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 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.
This directive obsoletes idassert-authcDN, idassert-passwd, idassert-
mode, and idassert-method.
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.
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.
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.
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 [{add|delete|modify|modrdn}=]<val> [...]
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.
tls {[try-]start|[try-]propagate}
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.
BACKWARD COMPATIBILITY
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.
server <hostname[:port]>
this directive is no longer supported. Use the uri directive as
described above.
acl-authcDN <administrative DN for access control purposes>
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 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.
acl-passwd <password>
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.
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 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.
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
/usr/internet/openldap/etc/slapd.conf
default slapd configuration file
SEE ALSO
slapd.conf(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
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