SLAPD-META(5) File Formats Manual SLAPD-META(5)
NAME
slapd-meta - metadirectory backend to slapd
SYNOPSIS
/etc/ldap/slapd.conf
DESCRIPTION
The meta backend to slapd(8) performs basic LDAP proxying with respect
to a set of remote LDAP servers, called "targets". The information con-
tained in these servers can be presented as belonging to a single Direc-
tory 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 in-
tended for proxying of multiple servers and possibly naming context mas-
querading. These features, although useful in many scenarios, may re-
sult 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-re-
lated 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 connec-
tion requires a new thread; as a consequence, the slapd(8) threads para-
meter 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.
EXAMPLES
There are examples in various places in this document, as well as in the
slapd/back-meta/data/ directory in the OpenLDAP source tree.
CONFIGURATION
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 at-
tributes related to entry creation and modification should not be prox-
ied, as they could be mistakenly written to the target server(s), gener-
ating an error. The current implementation automatically sets lastmod
to off, so its use is redundant and should be omitted.
SPECIAL CONFIGURATION DIRECTIVES
Target configuration starts with the "uri" directive. All the configu-
ration 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 <int>
This directive defines the maximum size of the privileged connec-
tions pool.
conn-ttl <time>
This directive causes a cached connection to be dropped an recre-
ated 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 al-
ter entries, in case of multiple matches an attempt is made to
perform the operation on any candidate target, with the con-
straint that at most one must succeed. This directive can also
be used when processing targets to mark a specific target as de-
fault.
dncache-ttl {DISABLED|forever|<ttl>}
This directive sets the time-to-live of the DN cache. This
caches the target that holds a given DN to speed up target selec-
tion 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, con-
tinue, 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 <NO|yes>
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 <NO|yes>
If yes, return success instead of searching if a filter is unde-
fined or contains undefined portions. By default, the search is
propagated after replacing undefined portions with (!(object-
Class=*)), which corresponds to the empty result set. If set be-
fore 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 de-
fined in each idassert-bind directive) to be deferred until actu-
ally needed by subsequent operations. Otherwise, all binds as
the rootdn are propagated to the targets.
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 in-
stead 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 pat-
tern.
rebind-as-user {NO|yes}
If this option is given, the client's bind credentials are remem-
bered for rebinds, when trying to re-establish a broken connec-
tion, 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 tar-
gets, 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
Target specification starts with a "uri" directive:
uri <protocol>://[<host>]/<naming context> [...]
The <protocol> part can be anything ldap_initialize(3) accepts
({ldap|ldaps|ldapi} and variants); the <host> may be omitted, de-
faulting to whatever is set in ldap.conf(5). The <naming con-
text> 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 <naming context> part doesn't need to be unique across the
targets; it may also match one of the values of the "suffix" di-
rective. Multiple URIs may be defined in a single URI statement.
The additional URIs must be separate arguments and must not have
any <naming context> 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 <administrative DN for access control purposes>
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. The acl-authcDN identity is by no means
implicitly used by the proxy when the client connects anony-
mously.
acl-passwd <password>
Password used with the acl-authcDN above.
bind-timeout <microseconds>
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, sub-
sequent calls use the value provided with bind-timeout. The de-
fault value is used also for subsequent calls if bind-timeout is
not specified. If set before any target specification, it af-
fects 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|<size>}
This feature allows one to use RFC 2696 Paged Results control
when performing search operations with a specific target, irre-
spective 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 (dis-
abled), 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 [<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 <target> as the
default one, starting from 1. Target <target> must be defined.
filter <pattern>
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 fil-
ter directive for each target.
idassert-authzFrom <authz-regexp>
if defined, selects what local identities are authorized to ex-
ploit 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_reqsan=never|allow|try|demand] [tls_cipher_suite=<ciphers>]
[tls_ecname=<ciphers>] [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 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. 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 <time>
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>d][<h>h][<m>m][<s>[s]]
where <d>, <h>, <m> and <s> 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 <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.
map {attribute|objectclass} [<local name>|*] {<foreign name>|*}
This maps object classes and attributes as in the LDAP backend.
See slapd-ldap(5).
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. If
set before any target specification, it affects all targets,
unless overridden by any per-target directive.
nretries {forever|never|<nretries>}
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} <rule>
This directive allows one to indicate what subtrees are actually
served by a target. The syntax of the supported rules is
<rule>: [dn[.<style>]:]<pattern>
<style>: subtree|children|regex
When <style> is either subtree or children the <pattern> is a DN
that must be within the naming context served by the target.
When <style> is regex the <pattern> is a regex(5) pattern. If
the dn.<style>: prefix is omitted, dn.subtree: is implicitly
assumed for backward compatibility.
In the subtree-exclude form if the request DN matches at least
one rule, the target is not considered while fulfilling the
request; otherwise, the target is considered based on the value
of the request DN. When the request is a search, also the scope
is considered.
In the subtree-include form if the request DN matches at least
one rule, the target is considered while fulfilling the request;
otherwise the target is ignored.
| match | exclude |
+---------+---------+-------------------+
| T | T | not candidate |
| F | T | continue checking |
+---------+---------+-------------------+
| T | F | candidate |
| F | F | not candidate |
+---------+---------+-------------------+
There may be multiple occurrences of the subtree-exclude or
subtree-include directive for each of the targets, but they are
mutually exclusive.
suffixmassage <virtual naming context> <real naming context>
All the directives starting with "rewrite" refer to the rewrite
engine that has been added to slapd. The "suffixmassage"
directive was introduced in the LDAP backend to allow suffix
massaging while proxying. It has been obsoleted by the rewriting
tools. However, both for backward compatibility and for ease of
configuration when simple suffix massage is required, it has been
preserved. It wraps the basic rewriting instructions that
perform suffix massaging. See the "REWRITING" section for a
detailed list of the rewrite rules it implies.
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. If set before any target
specification, it affects all targets, unless overridden by any
per-target directive.
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. If
specified before any target definition, it affects all targets
unless overridden by per-target directives.
Note: if the timeout 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.
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 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.
If set before any target specification, it affects all targets,
unless overridden by any per-target directive.
SCENARIOS
A powerful (and in some sense dangerous) rewrite engine has been added
to both the LDAP and Meta backends. While the former can gain limited
beneficial effects from rewriting stuff, the latter can become an
amazingly powerful tool.
Consider a couple of scenarios first.
1) Two directory servers share two levels of naming context; say
"dc=a,dc=foo,dc=com" and "dc=b,dc=foo,dc=com". Then, an unambiguous
Meta database can be configured as:
database meta
suffix "dc=foo,dc=com"
uri "ldap://a.foo.com/dc=a,dc=foo,dc=com"
uri "ldap://b.foo.com/dc=b,dc=foo,dc=com"
Operations directed to a specific target can be easily resolved because
there are no ambiguities. The only operation that may resolve to
multiple targets is a search with base "dc=foo,dc=com" and scope at
least "one", which results in spawning two searches to the targets.
2a) Two directory servers don't share any portion of naming context, but
they'd present as a single DIT [Caveat: uniqueness of (massaged) entries
among the two servers is assumed; integrity checks risk to incur in
excessive overhead and have not been implemented]. Say we have
"dc=bar,dc=org" and "o=Foo,c=US", and we'd like them to appear as
branches of "dc=foo,dc=com", say "dc=a,dc=foo,dc=com" and
"dc=b,dc=foo,dc=com". Then we need to configure our Meta backend as:
database meta
suffix "dc=foo,dc=com"
uri "ldap://a.bar.com/dc=a,dc=foo,dc=com"
suffixmassage "dc=a,dc=foo,dc=com" "dc=bar,dc=org"
uri "ldap://b.foo.com/dc=b,dc=foo,dc=com"
suffixmassage "dc=b,dc=foo,dc=com" "o=Foo,c=US"
Again, operations can be resolved without ambiguity, although some
rewriting is required. Notice that the virtual naming context of each
target is a branch of the database's naming context; it is rewritten
back and forth when operations are performed towards the target servers.
What "back and forth" means will be clarified later.
When a search with base "dc=foo,dc=com" is attempted, if the scope is
"base" it fails with "no such object"; in fact, the common root of the
two targets (prior to massaging) does not exist. If the scope is "one",
both targets are contacted with the base replaced by each target's base;
the scope is derated to "base". In general, a scope "one" search is
honored, and the scope is derated, only when the incoming base is at
most one level lower of a target's naming context (prior to massaging).
Finally, if the scope is "sub" the incoming base is replaced by each
target's unmassaged naming context, and the scope is not altered.
2b) Consider the above reported scenario with the two servers sharing
the same naming context:
database meta
suffix "dc=foo,dc=com"
uri "ldap://a.bar.com/dc=foo,dc=com"
suffixmassage "dc=foo,dc=com" "dc=bar,dc=org"
uri "ldap://b.foo.com/dc=foo,dc=com"
suffixmassage "dc=foo,dc=com" "o=Foo,c=US"
All the previous considerations hold, except that now there is no way to
unambiguously resolve a DN. In this case, all the operations that
require an unambiguous target selection will fail unless the DN is
already cached or a default target has been set. Practical
configurations may result as a combination of all the above scenarios.
ACLs
Note on ACLs: at present you may add whatever ACL rule you desire to the
Meta (and LDAP) backends. However, the meaning of an ACL on a proxy may
require some considerations. Two philosophies may be considered:
a) the remote server dictates the permissions; the proxy simply passes
back what it gets from the remote server.
b) the remote server unveils "everything"; the proxy is responsible for
protecting data from unauthorized access.
Of course the latter sounds unreasonable, but it is not. It is possible
to imagine scenarios in which a remote host discloses data that can be
considered "public" inside an intranet, and a proxy that connects it to
the internet may impose additional constraints. To this purpose, the
proxy should be able to comply with all the ACL matching criteria that
the server supports. This has been achieved with regard to all the
criteria supported by slapd except a special subtle case (please file an
ITS if you can find other exceptions: <http://www.openldap.org/its/>).
The rule
access to dn="<dn>" attrs=<attr>
by dnattr=<dnattr> read
by * none
cannot be matched iff the attribute that is being requested, <attr>, is
NOT <dnattr>, and the attribute that determines membership, <dnattr>,
has not been requested (e.g. in a search)
In fact this ACL is resolved by slapd using the portion of entry it
retrieved from the remote server without requiring any further
intervention of the backend, so, if the <dnattr> attribute has not been
fetched, the match cannot be assessed because the attribute is not
present, not because no value matches the requirement!
Note on ACLs and attribute mapping: ACLs are applied to the mapped
attributes; for instance, if the attribute locally known as "foo" is
mapped to "bar" on a remote server, then local ACLs apply to attribute
"foo" and are totally unaware of its remote name. The remote server
will check permissions for "bar", and the local server will possibly
enforce additional restrictions to "foo".
REWRITING
A string is rewritten according to a set of rules, called a `rewrite
context'. The rules are based on POSIX (''extended'') regular
expressions (regex) with substring matching; basic variable substitution
and map resolution of substrings is allowed by specific mechanisms
detailed in the following. The behavior of pattern
matching/substitution can be altered by a set of flags.
The underlying concept is to build a lightweight rewrite module for the
slapd server (initially dedicated to the LDAP backend).
Passes
An incoming string is matched against a set of rules. Rules are made of
a regex match pattern, a substitution pattern and a set of actions,
described by a set of flags. In case of match a string rewriting is
performed according to the substitution pattern that allows one to refer
to substrings matched in the incoming string. The actions, if any, are
finally performed. The substitution pattern allows map resolution of
substrings. A map is a generic object that maps a substitution pattern
to a value. The flags are divided in "Pattern matching Flags" and
"Action Flags"; the former alter the regex match pattern behavior while
the latter alter the action that is taken after substitution.
Pattern Matching Flags
`C' honors case in matching (default is case insensitive)
`R' use POSIX ''basic'' regular expressions (default is ''extended'')
`M{n}' allow no more than n recursive passes for a specific rule; does
not alter the max total count of passes, so it can only enforce a
stricter limit for a specific rule.
Action Flags
`:' apply the rule once only (default is recursive)
`@' stop applying rules in case of match; the current rule is still
applied recursively; combine with `:' to apply the current rule
only once and then stop.
`#' stop current operation if the rule matches, and issue an
`unwilling to perform' error.
`G{n}' jump n rules back and forth (watch for loops!). Note that `G{1}'
is implicit in every rule.
`I' ignores errors in rule; this means, in case of error, e.g. issued
by a map, the error is treated as a missed match. The `unwilling
to perform' is not overridden.
`U{n}' uses n as return code if the rule matches; the flag does not
alter the recursive behavior of the rule, so, to have it
performed only once, it must be used in combination with `:',
e.g. `:U{16}' returns the value `16' after exactly one execution
of the rule, if the pattern matches. As a consequence, its
behavior is equivalent to `@', with the return code set to n; or,
in other words, `@' is equivalent to `U{0}'. By convention, the
freely available codes are above 16 included; the others are
reserved.
The ordering of the flags can be significant. For instance: `IG{2}'
means ignore errors and jump two lines ahead both in case of match and
in case of error, while `G{2}I' means ignore errors, but jump two lines
ahead only in case of match.
More flags (mainly Action Flags) will be added as needed.
Pattern matching:
See regex(7) and/or re_format(7).
Substitution Pattern Syntax:
Everything starting with `%' requires substitution;
the only obvious exception is `%%', which is left as is;
the basic substitution is `%d', where `d' is a digit; 0 means the whole
string, while 1-9 is a submatch;
a `%' followed by a `{' invokes an advanced substitution. The pattern
is:
`%' `{' [ <op> ] <name> `(' <substitution> `)' `}'
where <name> must be a legal name for the map, i.e.
<name> ::= [a-z][a-z0-9]* (case insensitive)
<op> ::= `>' `|' `&' `&&' `*' `**' `$'
and <substitution> must be a legal substitution pattern, with no limits
on the nesting level.
The operators are:
> sub context invocation; <name> must be a legal, already defined
rewrite context name
| external command invocation; <name> must refer to a legal,
already defined command name (NOT IMPL.)
& variable assignment; <name> defines a variable in the running
operation structure which can be dereferenced later; operator &
assigns a variable in the rewrite context scope; operator &&
assigns a variable that scopes the entire session, e.g. its value
can be dereferenced later by other rewrite contexts
* variable dereferencing; <name> must refer to a variable that is
defined and assigned for the running operation; operator *
dereferences a variable scoping the rewrite context; operator **
dereferences a variable scoping the whole session, e.g. the value
is passed across rewrite contexts
$ parameter dereferencing; <name> must refer to an existing
parameter; the idea is to make some run-time parameters set by
the system available to the rewrite engine, as the client host
name, the bind DN if any, constant parameters initialized at
config time, and so on; no parameter is currently set by either
back-ldap or back-meta, but constant parameters can be defined in
the configuration file by using the rewriteParam directive.
Substitution escaping has been delegated to the `%' symbol, which is
used instead of `\' in string substitution patterns because `\' is
already escaped by slapd's low level parsing routines; as a consequence,
regex escaping requires two `\' symbols, e.g. `.*\.foo\.bar' must be
written as `.*\\.foo\\.bar'.
Rewrite context:
A rewrite context is a set of rules which are applied in sequence. The
basic idea is to have an application initialize a rewrite engine (think
of Apache's mod_rewrite ...) with a set of rewrite contexts; when string
rewriting is required, one invokes the appropriate rewrite context with
the input string and obtains the newly rewritten one if no errors occur.
Each basic server operation is associated to a rewrite context; they are
divided in two main groups: client -> server and server -> client
rewriting.
client -> server:
(default) if defined and no specific context
is available
bindDN bind
searchBase search
searchFilter search
searchFilterAttrDN search
compareDN compare
compareAttrDN compare AVA
addDN add
addAttrDN add AVA
modifyDN modify
modifyAttrDN modify AVA
modrDN modrdn
newSuperiorDN modrdn
deleteDN delete
exopPasswdDN password modify extended operation DN if proxy
server -> client:
searchResult search (only if defined; no default;
acts on DN and DN-syntax attributes
of search results)
searchAttrDN search AVA
matchedDN all ops (only if applicable)
Basic configuration syntax
rewriteEngine { on | off }
If `on', the requested rewriting is performed; if `off', no
rewriting takes place (an easy way to stop rewriting without
altering too much the configuration file).
rewriteContext <context name> [ alias <aliased context name> ]
<Context name> is the name that identifies the context, i.e. the
name used by the application to refer to the set of rules it
contains. It is used also to reference sub contexts in string
rewriting. A context may alias another one. In this case the
alias context contains no rule, and any reference to it will
result in accessing the aliased one.
rewriteRule <regex match pattern> <substitution pattern> [ <flags> ]
Determines how a string can be rewritten if a pattern is matched.
Examples are reported below.
Additional configuration syntax:
rewriteMap <map type> <map name> [ <map attrs> ]
Allows one to define a map that transforms substring rewriting
into something else. The map is referenced inside the
substitution pattern of a rule.
rewriteParam <param name> <param value>
Sets a value with global scope, that can be dereferenced by the
command `%{$paramName}'.
rewriteMaxPasses <number of passes> [<number of passes per rule>]
Sets the maximum number of total rewriting passes that can be
performed in a single rewrite operation (to avoid loops). A safe
default is set to 100; note that reaching this limit is still
treated as a success; recursive invocation of rules is simply
interrupted. The count applies to the rewriting operation as a
whole, not to any single rule; an optional per-rule limit can be
set. This limit is overridden by setting specific per-rule
limits with the `M{n}' flag.
Configuration examples:
# set to `off' to disable rewriting
rewriteEngine on
# the rules the "suffixmassage" directive implies
rewriteEngine on
# all dataflow from client to server referring to DNs
rewriteContext default
rewriteRule "(.*)<virtualnamingcontext>$" "%1<realnamingcontext>" ":"
# empty filter rule
rewriteContext searchFilter
# all dataflow from server to client
rewriteContext searchResult
rewriteRule "(.*)<realnamingcontext>$" "%1<virtualnamingcontext>" ":"
rewriteContext searchAttrDN alias searchResult
rewriteContext matchedDN alias searchResult
# Everything defined here goes into the `default' context.
# This rule changes the naming context of anything sent
# to `dc=home,dc=net' to `dc=OpenLDAP, dc=org'
rewriteRule "(.*)dc=home,[ ]?dc=net"
"%1dc=OpenLDAP, dc=org" ":"
# since a pretty/normalized DN does not include spaces
# after rdn separators, e.g. `,', this rule suffices:
rewriteRule "(.*)dc=home,dc=net"
"%1dc=OpenLDAP,dc=org" ":"
# Start a new context (ends input of the previous one).
# This rule adds blanks between DN parts if not present.
rewriteContext addBlanks
rewriteRule "(.*),([^ ].*)" "%1, %2"
# This one eats blanks
rewriteContext eatBlanks
rewriteRule "(.*),[ ](.*)" "%1,%2"
# Here control goes back to the default rewrite
# context; rules are appended to the existing ones.
# anything that gets here is piped into rule `addBlanks'
rewriteContext default
rewriteRule ".*" "%{>addBlanks(%0)}" ":"
# Rewrite the search base according to `default' rules.
rewriteContext searchBase alias default
# Search results with OpenLDAP DN are rewritten back with
# `dc=home,dc=net' naming context, with spaces eaten.
rewriteContext searchResult
rewriteRule "(.*[^ ]?)[ ]?dc=OpenLDAP,[ ]?dc=org"
"%{>eatBlanks(%1)}dc=home,dc=net" ":"
# Bind with email instead of full DN: we first need
# an ldap map that turns attributes into a DN (the
# argument used when invoking the map is appended to
# the URI and acts as the filter portion)
rewriteMap ldap attr2dn "ldap://host/dc=my,dc=org?dn?sub"
# Then we need to detect DN made up of a single email,
# e.g. `mail=someone@example.com'; note that the rule
# in case of match stops rewriting; in case of error,
# it is ignored. In case we are mapping virtual
# to real naming contexts, we also need to rewrite
# regular DNs, because the definition of a bindDn
# rewrite context overrides the default definition.
rewriteContext bindDN
rewriteRule "^mail=[^,]+@[^,]+$" "%{attr2dn(%0)}" ":@I"
# This is a rather sophisticated example. It massages a
# search filter in case who performs the search has
# administrative privileges. First we need to keep
# track of the bind DN of the incoming request, which is
# stored in a variable called `binddn' with session scope,
# and left in place to allow regular binding:
rewriteContext bindDN
rewriteRule ".+" "%{&&binddn(%0)}%0" ":"
# A search filter containing `uid=' is rewritten only
# if an appropriate DN is bound.
# To do this, in the first rule the bound DN is
# dereferenced, while the filter is decomposed in a
# prefix, in the value of the `uid=<arg>' AVA, and
# in a suffix. A tag `<>' is appended to the DN.
# If the DN refers to an entry in the `ou=admin' subtree,
# the filter is rewritten OR-ing the `uid=<arg>' with
# `cn=<arg>'; otherwise it is left as is. This could be
# useful, for instance, to allow apache's auth_ldap-1.4
# module to authenticate users with both `uid' and
# `cn', but only if the request comes from a possible
# `cn=Web auth,ou=admin,dc=home,dc=net' user.
rewriteContext searchFilter
rewriteRule "(.*\\()uid=([a-z0-9_]+)(\\).*)"
"%{**binddn}<>%{&prefix(%1)}%{&arg(%2)}%{&suffix(%3)}"
":I"
rewriteRule "[^,]+,ou=admin,dc=home,dc=net"
"%{*prefix}|(uid=%{*arg})(cn=%{*arg})%{*suffix}" ":@I"
rewriteRule ".*<>" "%{*prefix}uid=%{*arg}%{*suffix}" ":"
# This example shows how to strip unwanted DN-valued
# attribute values from a search result; the first rule
# matches DN values below "ou=People,dc=example,dc=com";
# in case of match the rewriting exits successfully.
# The second rule matches everything else and causes
# the value to be rejected.
rewriteContext searchResult
rewriteRule ".*,ou=People,dc=example,dc=com" "%0" ":@"
rewriteRule ".*" "" "#"
LDAP Proxy resolution (a possible evolution of slapd-ldap(5)):
In case the rewritten DN is an LDAP URI, the operation is initiated
towards the host[:port] indicated in the uri, if it does not refer to
the local server. E.g.:
rewriteRule '^cn=root,.*' '%0' 'G{3}'
rewriteRule '^cn=[a-l].*' 'ldap://ldap1.my.org/%0' ':@'
rewriteRule '^cn=[m-z].*' 'ldap://ldap2.my.org/%0' ':@'
rewriteRule '.*' 'ldap://ldap3.my.org/%0' ':@'
(Rule 1 is simply there to illustrate the `G{n}' action; it could have
been written:
rewriteRule '^cn=root,.*' 'ldap://ldap3.my.org/%0' ':@'
with the advantage of saving one rewrite pass ...)
ACCESS CONTROL
The meta 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.
PROXY CACHE OVERLAY
The proxy cache overlay allows caching of LDAP search requests (queries)
in a local database. See slapo-pcache(5) for details.
DEPRECATED STATEMENTS
The following statements have been deprecated and should no longer be
used.
pseudorootdn <substitute DN in case of rootdn bind>
Use idassert-bind instead.
pseudorootpw <substitute password in case of rootdn bind>
Use idassert-bind instead.
FILES
/etc/ldap/slapd.conf
default slapd configuration file
SEE ALSO
slapd.conf(5), slapd-asyncmeta(5), slapd-ldap(5), slapo-pcache(5),
slapd(8), regex(7), re_format(7).
AUTHOR
Pierangelo Masarati, based on back-ldap by Howard Chu
OpenLDAP 2.6.10+dfsg-1 2025/05/22 SLAPD-META(5)
Generated by dwww version 1.16 on Tue Dec 16 04:46:24 CET 2025.