The meta backend to slapd(8) performs basic LDAP proxying with
respect to a set of remote LDAP servers, called "targets". The
information contained in these servers can be presented as
belonging to a single Directory Information Tree (DIT).
A basic knowledge of the functionality of the slapd-ldap(5)
backend is recommended. This backend has been designed as an
enhancement of the ldap backend. The two backends share many
features (actually they also share portions of code). While the
ldap backend is intended to proxy operations directed to a single
server, the meta backend is mainly intended for proxying of
multiple servers and possibly naming context masquerading. These
features, although useful in many scenarios, may result in
excessive overhead for some applications, so its use should be
carefully considered. In the examples section, some typical
scenarios will be discussed.
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, the slapd(8)threads parameter may need some tuning. In those cases, unless the
multiple target feature is required, one may consider using
slapd-relay(5) instead, which performs the relayed operation
internally and thus reuses the same connection.
These slapd.conf options apply to the META backend database. That
is, they must follow a "database meta" 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 and back-meta 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.
Target configuration starts with the "uri" directive. All the
configuration directives that are not specific to targets should
be defined first for clarity, including those that are common to
all backends. They are:
conn-pool-max
This directive defines the maximum size of the privileged
connections pool.
conn-ttl
This directive causes a cached connection to be dropped an
recreated after a given ttl, regardless of being idle or
not.
default-target none
This directive forces the backend to reject all those
operations that must resolve to a single target in case
none or multiple targets are selected. They include: add,
delete, modify, modrdn; compare is not included, as well as
bind since, as they don't alter entries, in case of
multiple matches an attempt is made to perform the
operation on any candidate target, with the constraint that
at most one must succeed. This directive can also be used
when processing targets to mark a specific target as
default.
dncache-ttl {DISABLED|forever|}
This directive sets the time-to-live of the DN cache. This
caches the target that holds a given DN to speed up target
selection in case multiple targets would result from an
uncached search; forever means cache never expires;
disabled means no DN caching; otherwise a valid ( > 0 ) ttl
is required, in the format illustrated for the idle-timeout
directive.
onerr {CONTINUE|report|stop}
This directive allows one to select the behavior in case an
error is returned by one target during a search. The
default, continue, consists in continuing the operation,
trying to return as much data as possible. If the value is
set to stop, the search is terminated as soon as an error
is returned by one target, and the error is immediately
propagated to the client. If the value is set to report,
the search is continued to the end but, in case at least
one target returned an error code, the first non-success
error code is returned.
norefs
If yes, do not return search reference responses. By
default, they are returned unless request is LDAPv2. If
set before any target specification, it affects all
targets, unless overridden by any per-target directive.
noundeffilter
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. If set before any target specification, it
affects all targets, unless overridden by any per-target
directive.
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. If
set before any target specification, it affects all
targets, unless overridden by any per-target directive.
pseudoroot-bind-defer {YES|no}
This directive, when set to yes, causes the authentication
to the remote servers with the pseudo-root identity (the
identity defined in each idassert-bind directive) to be
deferred until actually needed by subsequent operations.
Otherwise, all binds as the rootdn are propagated to the
targets.
quarantine ,[;,[...]]
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. This directive must appear before any
target specification; it affects all targets with the same
pattern.
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. If set before any
target specification, it affects all targets, unless
overridden by any per-target directive.
single-conn {NO|yes}
Discards current cached connection when the client rebinds.
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.
Target specification starts with a "uri" directive:
uri ://[]/ [...]
The part can be anything ldap_initialize(3)
accepts ({ldap|ldaps|ldapi} and variants); the may
be omitted, defaulting to whatever is set in ldap.conf(5).
The part is mandatory for the first URI,
but it must be omitted for subsequent ones, if any. The
naming context part must be within the naming context
defined for the backend, e.g.:
suffix "dc=foo,dc=com"
uri "ldap://x.foo.com/dc=x,dc=foo,dc=com"
The part doesn't need to be unique across
the targets; it may also match one of the values of the
"suffix" directive. Multiple URIs may be defined in a
single URI statement. The additional URIs must be separate
arguments and must not have any part.
This causes the underlying library to contact the first
server of the list that responds. For example, if
l1.foo.com and l2.foo.com are shadows of the same server,
the directive
suffix "dc=foo,dc=com"
uri "ldap://l1.foo.com/dc=foo,dc=com" "ldap://l2.foo.com/"
causes l2.foo.com to be contacted whenever l1.foo.com does
not respond. In that case, the URI list is internally
rearranged, by moving unavailable URIs to the end, so that
further connection attempts occur with respect to the last
URI that succeeded.
acl-authcDN
DN which is used to query the target server for acl
checking, as in the LDAP backend; 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. Theacl-authcDN identity is by no means implicitly used by theproxy when the client connects anonymously.acl-passwd
Password used with the acl-authcDN above.
bind-timeout
This directive defines the timeout, in microseconds, used
when polling for response after an asynchronous bind
connection. The initial call to ldap_result(3) is
performed with a trade-off timeout of 100000 us; if that
results in a timeout exceeded, subsequent calls use the
value provided with bind-timeout. The default value is
used also for subsequent calls if bind-timeout is not
specified. If set before any target specification, it
affects all targets, unless overridden by any per-target
directive.
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. If set before
any target specification, it affects all targets, unless
overridden by any per-target directive.
client-pr {accept-unsolicited|DISABLE|}
This feature allows one to use RFC 2696 Paged Results
control when performing search operations with a specific
target, irrespective of the client's request. When set to
a numeric value, Paged Results control is always used with
size as the page size. When set to accept-unsolicited,
unsolicited Paged Results control responses are accepted
and honored for compatibility with broken remote DSAs. The
client is not exposed to paged results handling between
slapd-meta(5) and the remote servers. By default
(disabled), Paged Results control is not used and responses
are not accepted. If set before any target specification,
it affects all targets, unless overridden by any per-target
directive.
default-target []
The "default-target" directive can also be used during
target specification. With no arguments it marks the
current target as the default. The optional number marks
target as the default one, starting from 1.
Target must be defined.
filter
This directive allows specifying a regex(5) pattern to
indicate what search filter terms are actually served by a
target.
In a search request, if the search filter matches the
pattern the target is considered while fulfilling the
request; otherwise the target is ignored. There may be
multiple occurrences of the filter directive for each
target.
idassert-authzFrom
if defined, selects what local identities are authorized to
exploit the identity assertion feature. The string
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=][credentials=] [saslmech=][secprops=] [realm=][authcId=] [authzId=][authz={native|proxyauthz}] [mode=] [flags=][starttls=no|yes|critical] [tls_cert=][tls_key=] [tls_cacert=] [tls_cacertdir=][tls_reqcert=never|allow|try|demand][tls_reqsan=never|allow|try|demand][tls_cipher_suite=] [tls_ecname=][tls_protocol_min=[.]][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. 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:
:= {legacy|anonymous|none|self}
If is not present, and authzId is given, the proxy
always authorizes that identity. can be
u:[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 . 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. When bindmethod is SASL, the authcDN
must be specified in addition to the authcID, although it
is not used within the authentication process.
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", 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.
idle-timeout
This directive causes a cached connection to be dropped an
recreated after it has been idle for the specified time.
The value can be specified as
[d][h][m][[s]]
where , , and are respectively treated as
days, hours, minutes and seconds. If set before any target
specification, it affects all targets, unless overridden by
any per-target directive.
keepalive ::
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
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.
map {attribute|objectclass} [|*] {|*}
This maps object classes and attributes as in the LDAP
backend. See slapd-ldap(5).
network-timeout
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. If set before any target
specification, it affects all targets, unless overridden by
any per-target directive.
nretries {forever|never|}
This directive defines how many times a bind should be
retried in case of temporary failure in contacting a
target. If defined before any target specification, it
applies to all targets (by default, 3 times); the global
value can be overridden by redefinitions inside each target
specification.
rewrite* ...
The rewrite options are described in the "REWRITING"
section.
subtree-{exclude|include}
This directive allows one to indicate what subtrees are
actually served by a target. The syntax of the supported
rules is
: [dn[.