1SLAPD-META(5) File Formats Manual SLAPD-META(5)
2
6 slapd-meta - metadirectory backend to slapd
7
9 /etc/openldap/slapd.conf
10
12 The meta backend to slapd(8) performs basic LDAP proxying with respect
13 to a set of remote LDAP servers, called "targets". The information
14 contained in these servers can be presented as belonging to a single
15 Directory Information Tree (DIT).
16 A basic knowledge of the functionality of the slapd-ldap(5) backend is
18 recommended. This backend has been designed as an enhancement of the
19 ldap backend. The two backends share many features (actually they also
20 share portions of code). While the ldap backend is intended to proxy
21 operations directed to a single server, the meta backend is mainly in‐
22 tended for proxying of multiple servers and possibly naming context
23 masquerading. These features, although useful in many scenarios, may
24 result in excessive overhead for some applications, so its use should
25 be carefully considered. In the examples section, some typical scenar‐
26 ios will be discussed.
27 The proxy instance of slapd(8) must contain schema information for the
29 attributes and objectClasses used in filters, request DN and request-
30 related data in general. It should also contain schema information for
31 the data returned by the proxied server. It is the responsibility of
32 the proxy administrator to keep the schema of the proxy lined up with
33 that of the proxied server.
34 Note: When looping back to the same instance of slapd(8), each connec‐
37 tion requires a new thread; as a consequence, slapd(8) must be compiled
38 with thread support, and the threads parameter may need some tuning; in
39 those cases, unless the multiple target feature is required, one may
40 consider using slapd-relay(5) instead, which performs the relayed oper‐
41 ation internally and thus reuses the same connection.
42
45 There are examples in various places in this document, as well as in
46 the slapd/back-meta/data/ directory in the OpenLDAP source tree.
47
49 These slapd.conf options apply to the META backend database. That is,
50 they must follow a "database meta" line and come before any subsequent
51 "backend" or "database" lines. Other database options are described in
52 the slapd.conf(5) manual page.
53 Note: In early versions of back-ldap and back-meta it was recommended
55 to always set
56 lastmod off
58 for ldap and meta databases. This was required because operational at‐
60 tributes related to entry creation and modification should not be prox‐
61 ied, as they could be mistakenly written to the target server(s), gen‐
62 erating an error. The current implementation automatically sets last‐
63 mod to off, so its use is redundant and should be omitted.
64
67 Target configuration starts with the "uri" directive. All the configu‐
68 ration directives that are not specific to targets should be defined
69 first for clarity, including those that are common to all backends.
70 They are:
71 conn-ttl <time>
74 This directive causes a cached connection to be dropped an
75 recreated after a given ttl, regardless of being idle or not.
76 default-target none
79 This directive forces the backend to reject all those operations
80 that must resolve to a single target in case none or multiple
81 targets are selected. They include: add, delete, modify, mod‐
82 rdn; compare is not included, as well as bind since, as they
83 don't alter entries, in case of multiple matches an attempt is
84 made to perform the operation on any candidate target, with the
85 constraint that at most one must succeed. This directive can
86 also be used when processing targets to mark a specific target
87 as default.
88 dncache-ttl {DISABLED|forever|<ttl>}
91 This directive sets the time-to-live of the DN cache. This
92 caches the target that holds a given DN to speed up target se‐
93 lection in case multiple targets would result from an uncached
94 search; forever means cache never expires; disabled means no DN
95 caching; otherwise a valid ( > 0 ) ttl is required, in the for‐
96 mat illustrated for the idle-timeout directive.
97 onerr {CONTINUE|report|stop}
100 This directive allows one to select the behavior in case an er‐
101 ror is returned by one target during a search. The default,
102 continue, consists in continuing the operation, trying to return
103 as much data as possible. If the value is set to stop, the
104 search is terminated as soon as an error is returned by one tar‐
105 get, and the error is immediately propagated to the client. If
106 the value is set to report, the search is continuated to the end
107 but, in case at least one target returned an error code, the
108 first non-success error code is returned.
109 norefs <NO|yes>
112 If yes, do not return search reference responses. By default,
113 they are returned unless request is LDAPv2. If set before any
114 target specification, it affects all targets, unless overridden
115 by any per-target directive.
116 noundeffilter <NO|yes>
119 If yes, return success instead of searching if a filter is unde‐
120 fined or contains undefined portions. By default, the search is
121 propagated after replacing undefined portions with (!(object‐
122 Class=*)), which corresponds to the empty result set. If set
123 before any target specification, it affects all targets, unless
124 overridden by any per-target directive.
125 protocol-version {0,2,3}
128 This directive indicates what protocol version must be used to
129 contact the remote server. If set to 0 (the default), the proxy
130 uses the same protocol version used by the client, otherwise the
131 requested protocol is used. The proxy returns unwillingToPer‐
132 form if an operation that is incompatible with the requested
133 protocol is attempted. If set before any target specification,
134 it affects all targets, unless overridden by any per-target di‐
135 rective.
136 pseudoroot-bind-defer {YES|no}
139 This directive, when set to yes, causes the authentication to
140 the remote servers with the pseudo-root identity (the identity
141 defined in each idassert-bind directive) to be deferred until
142 actually needed by subsequent operations. Otherwise, all binds
143 as the rootdn are propagated to the targets.
144 quarantine <interval>,<num>[;<interval>,<num>[...]]
147 Turns on quarantine of URIs that returned LDAP_UNAVAILABLE, so
148 that an attempt to reconnect only occurs at given intervals in‐
149 stead of any time a client requests an operation. The pattern
150 is: retry only after at least interval seconds elapsed since
151 last attempt, for exactly num times; then use the next pattern.
152 If num for the last pattern is "+", it retries forever; other‐
153 wise, no more retries occur. This directive must appear before
154 any target specification; it affects all targets with the same
155 pattern.
156 rebind-as-user {NO|yes}
159 If this option is given, the client's bind credentials are re‐
160 membered for rebinds, when trying to re-establish a broken con‐
161 nection, or when chasing a referral, if chase-referrals is set
162 to yes.
163 session-tracking-request {NO|yes}
166 Adds session tracking control for all requests. The client's IP
167 and hostname, and the identity associated to each request, if
168 known, are sent to the remote server for informational purposes.
169 This directive is incompatible with setting protocol-version to
170 2. If set before any target specification, it affects all tar‐
171 gets, unless overridden by any per-target directive.
172 single-conn {NO|yes}
175 Discards current cached connection when the client rebinds.
176 use-temporary-conn {NO|yes}
179 when set to yes, create a temporary connection whenever compet‐
180 ing with other threads for a shared one; otherwise, wait until
181 the shared connection is available.
182
185 Target specification starts with a "uri" directive:
186 uri <protocol>://[<host>]/<naming context> [...]
189 The <protocol> part can be anything ldap_initialize(3) accepts
190 ({ldap|ldaps|ldapi} and variants); the <host> may be omitted,
191 defaulting to whatever is set in ldap.conf(5). The <naming con‐
192 text> part is mandatory for the first URI, but it must be omit‐
193 ted for subsequent ones, if any. The naming context part must
194 be within the naming context defined for the backend, e.g.:
195 suffix "dc=foo,dc=com"
197 uri "ldap://x.foo.com/dc=x,dc=foo,dc=com"
198 The <naming context> part doesn't need to be unique across the
200 targets; it may also match one of the values of the "suffix" di‐
201 rective. Multiple URIs may be defined in a single URI state‐
202 ment. The additional URIs must be separate arguments and must
203 not have any <naming context> part. This causes the underlying
204 library to contact the first server of the list that responds.
205 For example, if l1.foo.com and l2.foo.com are shadows of the
206 same server, the directive
207 suffix "dc=foo,dc=com"
209 uri "ldap://l1.foo.com/dc=foo,dc=com" "ldap://l2.foo.com/"
210 causes l2.foo.com to be contacted whenever l1.foo.com does not
212 respond. In that case, the URI list is internally rearranged,
213 by moving unavailable URIs to the end, so that further connec‐
214 tion attempts occur with respect to the last URI that succeeded.
215 acl-authcDN <administrative DN for access control purposes>
218 DN which is used to query the target server for acl checking, as
219 in the LDAP backend; it is supposed to have read access on the
220 target server to attributes used on the proxy for acl checking.
221 There is no risk of giving away such values; they are only used
222 to check permissions. The acl-authcDN identity is by no means
223 implicitly used by the proxy when the client connects anony‐
224 mously.
225 acl-passwd <password>
228 Password used with the acl-authcDN above.
229 bind-timeout <microseconds>
232 This directive defines the timeout, in microseconds, used when
233 polling for response after an asynchronous bind connection. The
234 initial call to ldap_result(3) is performed with a trade-off
235 timeout of 100000 us; if that results in a timeout exceeded,
236 subsequent calls use the value provided with bind-timeout. The
237 default value is used also for subsequent calls if bind-timeout
238 is not specified. If set before any target specification, it
239 affects all targets, unless overridden by any per-target direc‐
240 tive.
241 chase-referrals {YES|no}
244 enable/disable automatic referral chasing, which is delegated to
245 the underlying libldap, with rebinding eventually performed if
246 the rebind-as-user directive is used. The default is to chase
247 referrals. If set before any target specification, it affects
248 all targets, unless overridden by any per-target directive.
249 default-target [<target>]
252 The "default-target" directive can also be used during target
253 specification. With no arguments it marks the current target as
254 the default. The optional number marks target <target> as the
255 default one, starting from 1. Target <target> must be defined.
256 filter <pattern>
259 This directive allows specifying a regex(5) pattern to indicate
260 what search filter terms are actually served by a target.
261 In a search request, if the search filter matches the pattern
263 the target is considered while fulfilling the request; otherwise
264 the target is ignored. There may be multiple occurrences of the
265 filter directive for each target.
266 idassert-authzFrom <authz-regexp>
269 if defined, selects what local identities are authorized to ex‐
270 ploit the identity assertion feature. The string <authz-regexp>
271 follows the rules defined for the authzFrom attribute. See
272 slapd.conf(5), section related to authz-policy, for details on
273 the syntax of this field.
274 idassert-bind bindmethod=none|simple|sasl [binddn=<simple DN>]
277 [credentials=<simple password>] [saslmech=<SASL mech>]
278 [secprops=<properties>] [realm=<realm>] [authcId=<authentication
279 ID>] [authzId=<authorization ID>] [authz={native|proxyauthz}]
280 [mode=<mode>] [flags=<flags>] [starttls=no|yes|critical]
281 [tls_cert=<file>] [tls_key=<file>] [tls_cacert=<file>]
282 [tls_cacertdir=<path>] [tls_reqcert=never|allow|try|demand]
283 [tls_reqsan=never|allow|try|demand] [tls_cipher_suite=<ciphers>]
284 [tls_ecname=<ciphers>] [tls_protocol_min=<major>[.<minor>]]
285 [tls_crlcheck=none|peer|all]
286 Allows one to define the parameters of the authentication method
287 that is internally used by the proxy to authorize connections
288 that are authenticated by other databases. The identity defined
289 by this directive, according to the properties associated to the
290 authentication method, is supposed to have auth access on the
291 target server to attributes used on the proxy for authentication
292 and authorization, and to be allowed to authorize the users.
293 This requires to have proxyAuthz privileges on a wide set of
294 DNs, e.g. authzTo=dn.subtree:"", and the remote server to have
295 authz-policy set to to or both. See slapd.conf(5) for details
296 on these statements and for remarks and drawbacks about their
297 usage. The supported bindmethods are
298 none|simple|sasl
300 where none is the default, i.e. no identity assertion is
302 performed.
303 The authz parameter is used to instruct the SASL bind to exploit
305 native SASL authorization, if available; since connections are
306 cached, this should only be used when authorizing with a fixed
307 identity (e.g. by means of the authzDN or authzID parameters).
308 Otherwise, the default proxyauthz is used, i.e. the proxyAuthz
309 control (Proxied Authorization, RFC 4370) is added to all
310 operations.
311 The supported modes are:
313 <mode> := {legacy|anonymous|none|self}
315 If <mode> is not present, and authzId is given, the proxy always
317 authorizes that identity. <authorization ID> can be
318 u:<user>
320 [dn:]<DN>
322 The former is supposed to be expanded by the remote server
324 according to the authz rules; see slapd.conf(5) for details. In
325 the latter case, whether or not the dn: prefix is present, the
326 string must pass DN validation and normalization.
327 The default mode is legacy, which implies that the proxy will
329 either perform a simple bind as the authcDN or a SASL bind as
330 the authcID and assert the client's identity when it is not
331 anonymous. Direct binds are always proxied. The other modes
332 imply that the proxy will always either perform a simple bind as
333 the authcDN or a SASL bind as the authcID, unless restricted by
334 idassert-authzFrom rules (see below), in which case the
335 operation will fail; eventually, it will assert some other
336 identity according to <mode>. Other identity assertion modes
337 are anonymous and self, which respectively mean that the empty
338 or the client's identity will be asserted; none, which means
339 that no proxyAuthz control will be used, so the authcDN or the
340 authcID identity will be asserted. For all modes that require
341 the use of the proxyAuthz control, on the remote server the
342 proxy identity must have appropriate authzTo permissions, or the
343 asserted identities must have appropriate authzFrom permissions.
344 Note, however, that the ID assertion feature is mostly useful
345 when the asserted identities do not exist on the remote server.
346 Flags can be
348 override,[non-]prescriptive,proxy-authz-[non-]critical
350 When the override flag is used, identity assertion takes place
352 even when the database is authorizing for the identity of the
353 client, i.e. after binding with the provided identity, and thus
354 authenticating it, the proxy performs the identity assertion
355 using the configured identity and authentication method.
356 When the prescriptive flag is used (the default), operations
358 fail with inappropriateAuthentication for those identities whose
359 assertion is not allowed by the idassert-authzFrom patterns. If
360 the non-prescriptive flag is used, operations are performed
361 anonymously for those identities whose assertion is not allowed
362 by the idassert-authzFrom patterns.
363 When the proxy-authz-non-critical flag is used (the default),
365 the proxyAuthz control is not marked as critical, in violation
366 of RFC 4370. Use of proxy-authz-critical is recommended.
367 The TLS settings default to the same as the main slapd TLS
369 settings, except for tls_reqcert which defaults to "demand", and
370 tls_reqsan which defaults to "allow"..
371 The identity associated to this directive is also used for
373 privileged operations whenever idassert-bind is defined and
374 acl-bind is not. See acl-bind for details.
375 idle-timeout <time>
378 This directive causes a cached connection to be dropped an
379 recreated after it has been idle for the specified time. The
380 value can be specified as
381 [<d>d][<h>h][<m>m][<s>[s]]
383 where <d>, <h>, <m> and <s> are respectively treated as days,
385 hours, minutes and seconds. If set before any target
386 specification, it affects all targets, unless overridden by any
387 per-target directive.
388 keepalive <idle>:<probes>:<interval>
391 The keepalive parameter sets the values of idle, probes, and
392 interval used to check whether a socket is alive; idle is the
393 number of seconds a connection needs to remain idle before TCP
394 starts sending keepalive probes; probes is the maximum number of
395 keepalive probes TCP should send before dropping the connection;
396 interval is interval in seconds between individual keepalive
397 probes. Only some systems support the customization of these
398 values; the keepalive parameter is ignored otherwise, and
399 system-wide settings are used.
400 map {attribute|objectclass} [<local name>|*] {<foreign name>|*}
403 This maps object classes and attributes as in the LDAP backend.
404 See slapd-ldap(5).
405 network-timeout <time>
408 Sets the network timeout value after which poll(2)/select(2)
409 following a connect(2) returns in case of no activity. The
410 value is in seconds, and it can be specified as for
411 idle-timeout. If set before any target specification, it
412 affects all targets, unless overridden by any per-target
413 directive.
414 nretries {forever|never|<nretries>}
417 This directive defines how many times a bind should be retried
418 in case of temporary failure in contacting a target. If defined
419 before any target specification, it applies to all targets (by
420 default, 3 times); the global value can be overridden by
421 redefinitions inside each target specification.
422 rewrite* ...
425 The rewrite options are described in the "REWRITING" section.
426 subtree-{exclude|include} <rule>
429 This directive allows one to indicate what subtrees are actually
430 served by a target. The syntax of the supported rules is
431 <rule>: [dn[.<style>]:]<pattern>
433 <style>: subtree|children|regex
435 When <style> is either subtree or children the <pattern> is a DN
437 that must be within the naming context served by the target.
438 When <style> is regex the <pattern> is a regex(5) pattern. If
439 the dn.<style>: prefix is omitted, dn.subtree: is implicitly
440 assumed for backward compatibility.
441 In the subtree-exclude form if the request DN matches at least
443 one rule, the target is not considered while fulfilling the
444 request; otherwise, the target is considered based on the value
445 of the request DN. When the request is a search, also the scope
446 is considered.
447 In the subtree-include form if the request DN matches at least
449 one rule, the target is considered while fulfilling the request;
450 otherwise the target is ignored.
451 | match | exclude |
454 +---------+---------+-------------------+
455 | T | T | not candidate |
456 | F | T | continue checking |
457 +---------+---------+-------------------+
458 | T | F | candidate |
459 | F | F | not candidate |
460 +---------+---------+-------------------+
461 There may be multiple occurrences of the subtree-exclude or
463 subtree-include directive for each of the targets, but they are
464 mutually exclusive.
465 suffixmassage <virtual naming context> <real naming context>
468 All the directives starting with "rewrite" refer to the rewrite
469 engine that has been added to slapd. The "suffixmassage"
470 directive was introduced in the LDAP backend to allow suffix
471 massaging while proxying. It has been obsoleted by the
472 rewriting tools. However, both for backward compatibility and
473 for ease of configuration when simple suffix massage is
474 required, it has been preserved. It wraps the basic rewriting
475 instructions that perform suffix massaging. See the "REWRITING"
476 section for a detailed list of the rewrite rules it implies.
477 t-f-support {NO|yes|discover}
480 enable if the remote server supports absolute filters (see RFC
481 4526 for details). If set to discover, support is detected by
482 reading the remote server's root DSE. If set before any target
483 specification, it affects all targets, unless overridden by any
484 per-target directive.
485 timeout [<op>=]<val> [...]
488 This directive allows one to set per-operation timeouts.
489 Operations can be
490 <op> ::= bind, add, delete, modrdn, modify, compare, search
492 The overall duration of the search operation is controlled
494 either by the timelimit parameter or by server-side enforced
495 time limits (see timelimit and limits in slapd.conf(5) for
496 details). This timeout parameter controls how long the target
497 can be irresponsive before the operation is aborted. Timeout is
498 meaningless for the remaining operations, unbind and abandon,
499 which do not imply any response, while it is not yet implemented
500 in currently supported extended operations. If no operation is
501 specified, the timeout val affects all supported operations. If
502 specified before any target definition, it affects all targets
503 unless overridden by per-target directives.
504 Note: if the timeout is exceeded, the operation is cancelled
506 (according to the cancel directive); the protocol does not
507 provide any means to rollback operations, so the client will not
508 be notified about the result of the operation, which may
509 eventually succeeded or not. In case the timeout is exceeded
510 during a bind operation, the connection is destroyed, according
511 to RFC4511.
512 tls {[try-]start|[try-]propagate}
515 execute the StartTLS extended operation when the connection is
516 initialized; only works if the URI directive protocol scheme is
517 not ldaps://. propagate issues the StartTLS operation only if
518 the original connection did. The try- prefix instructs the
519 proxy to continue operations if the StartTLS operation failed;
520 its use is highly deprecated. If set before any target
521 specification, it affects all targets, unless overridden by any
522 per-target directive.
523
526 A powerful (and in some sense dangerous) rewrite engine has been added
527 to both the LDAP and Meta backends. While the former can gain limited
528 beneficial effects from rewriting stuff, the latter can become an
529 amazingly powerful tool.
530 Consider a couple of scenarios first.
532 1) Two directory servers share two levels of naming context; say
534 "dc=a,dc=foo,dc=com" and "dc=b,dc=foo,dc=com". Then, an unambiguous
535 Meta database can be configured as:
536 database meta
538 suffix "dc=foo,dc=com"
539 uri "ldap://a.foo.com/dc=a,dc=foo,dc=com"
540 uri "ldap://b.foo.com/dc=b,dc=foo,dc=com"
541 Operations directed to a specific target can be easily resolved because
543 there are no ambiguities. The only operation that may resolve to
544 multiple targets is a search with base "dc=foo,dc=com" and scope at
545 least "one", which results in spawning two searches to the targets.
546 2a) Two directory servers don't share any portion of naming context,
548 but they'd present as a single DIT [Caveat: uniqueness of (massaged)
549 entries among the two servers is assumed; integrity checks risk to
550 incur in excessive overhead and have not been implemented]. Say we
551 have "dc=bar,dc=org" and "o=Foo,c=US", and we'd like them to appear as
552 branches of "dc=foo,dc=com", say "dc=a,dc=foo,dc=com" and
553 "dc=b,dc=foo,dc=com". Then we need to configure our Meta backend as:
554 database meta
556 suffix "dc=foo,dc=com"
557 uri "ldap://a.bar.com/dc=a,dc=foo,dc=com"
559 suffixmassage "dc=a,dc=foo,dc=com" "dc=bar,dc=org"
560 uri "ldap://b.foo.com/dc=b,dc=foo,dc=com"
562 suffixmassage "dc=b,dc=foo,dc=com" "o=Foo,c=US"
563 Again, operations can be resolved without ambiguity, although some
565 rewriting is required. Notice that the virtual naming context of each
566 target is a branch of the database's naming context; it is rewritten
567 back and forth when operations are performed towards the target
568 servers. What "back and forth" means will be clarified later.
569 When a search with base "dc=foo,dc=com" is attempted, if the scope is
571 "base" it fails with "no such object"; in fact, the common root of the
572 two targets (prior to massaging) does not exist. If the scope is
573 "one", both targets are contacted with the base replaced by each
574 target's base; the scope is derated to "base". In general, a scope
575 "one" search is honored, and the scope is derated, only when the
576 incoming base is at most one level lower of a target's naming context
577 (prior to massaging).
578 Finally, if the scope is "sub" the incoming base is replaced by each
580 target's unmassaged naming context, and the scope is not altered.
581 2b) Consider the above reported scenario with the two servers sharing
583 the same naming context:
584 database meta
586 suffix "dc=foo,dc=com"
587 uri "ldap://a.bar.com/dc=foo,dc=com"
589 suffixmassage "dc=foo,dc=com" "dc=bar,dc=org"
590 uri "ldap://b.foo.com/dc=foo,dc=com"
592 suffixmassage "dc=foo,dc=com" "o=Foo,c=US"
593 All the previous considerations hold, except that now there is no way
595 to unambiguously resolve a DN. In this case, all the operations that
596 require an unambiguous target selection will fail unless the DN is
597 already cached or a default target has been set. Practical
598 configurations may result as a combination of all the above scenarios.
599
601 Note on ACLs: at present you may add whatever ACL rule you desire to
602 the Meta (and LDAP) backends. However, the meaning of an ACL on a
603 proxy may require some considerations. Two philosophies may be
604 considered:
605 a) the remote server dictates the permissions; the proxy simply passes
607 back what it gets from the remote server.
608 b) the remote server unveils "everything"; the proxy is responsible for
610 protecting data from unauthorized access.
611 Of course the latter sounds unreasonable, but it is not. It is
613 possible to imagine scenarios in which a remote host discloses data
614 that can be considered "public" inside an intranet, and a proxy that
615 connects it to the internet may impose additional constraints. To this
616 purpose, the proxy should be able to comply with all the ACL matching
617 criteria that the server supports. This has been achieved with regard
618 to all the criteria supported by slapd except a special subtle case
619 (please file an ITS if you can find other exceptions:
620 <http://www.openldap.org/its/>). The rule
621 access to dn="<dn>" attrs=<attr>
623 by dnattr=<dnattr> read
624 by * none
625 cannot be matched iff the attribute that is being requested, <attr>, is
627 NOT <dnattr>, and the attribute that determines membership, <dnattr>,
628 has not been requested (e.g. in a search)
629 In fact this ACL is resolved by slapd using the portion of entry it
631 retrieved from the remote server without requiring any further
632 intervention of the backend, so, if the <dnattr> attribute has not been
633 fetched, the match cannot be assessed because the attribute is not
634 present, not because no value matches the requirement!
635 Note on ACLs and attribute mapping: ACLs are applied to the mapped
637 attributes; for instance, if the attribute locally known as "foo" is
638 mapped to "bar" on a remote server, then local ACLs apply to attribute
639 "foo" and are totally unaware of its remote name. The remote server
640 will check permissions for "bar", and the local server will possibly
641 enforce additional restrictions to "foo".
642
644 A string is rewritten according to a set of rules, called a `rewrite
645 context'. The rules are based on POSIX (''extended'') regular
646 expressions (regex) with substring matching; basic variable
647 substitution and map resolution of substrings is allowed by specific
648 mechanisms detailed in the following. The behavior of pattern
649 matching/substitution can be altered by a set of flags.
650 The underlying concept is to build a lightweight rewrite module for the
652 slapd server (initially dedicated to the LDAP backend).
653
655 An incoming string is matched against a set of rules. Rules are made
656 of a regex match pattern, a substitution pattern and a set of actions,
657 described by a set of flags. In case of match a string rewriting is
658 performed according to the substitution pattern that allows one to
659 refer to substrings matched in the incoming string. The actions, if
660 any, are finally performed. The substitution pattern allows map
661 resolution of substrings. A map is a generic object that maps a
662 substitution pattern to a value. The flags are divided in "Pattern
663 matching Flags" and "Action Flags"; the former alter the regex match
664 pattern behavior while the latter alter the action that is taken after
665 substitution.
666
668 `C' honors case in matching (default is case insensitive)
669 `R' use POSIX ''basic'' regular expressions (default is
671 ''extended'')
672 `M{n}' allow no more than n recursive passes for a specific rule; does
674 not alter the max total count of passes, so it can only enforce
675 a stricter limit for a specific rule.
676
678 `:' apply the rule once only (default is recursive)
679 `@' stop applying rules in case of match; the current rule is still
681 applied recursively; combine with `:' to apply the current rule
682 only once and then stop.
683 `#' stop current operation if the rule matches, and issue an
685 `unwilling to perform' error.
686 `G{n}' jump n rules back and forth (watch for loops!). Note that
688 `G{1}' is implicit in every rule.
689 `I' ignores errors in rule; this means, in case of error, e.g.
691 issued by a map, the error is treated as a missed match. The
692 `unwilling to perform' is not overridden.
693 `U{n}' uses n as return code if the rule matches; the flag does not
695 alter the recursive behavior of the rule, so, to have it
696 performed only once, it must be used in combination with `:',
697 e.g. `:U{16}' returns the value `16' after exactly one
698 execution of the rule, if the pattern matches. As a
699 consequence, its behavior is equivalent to `@', with the return
700 code set to n; or, in other words, `@' is equivalent to `U{0}'.
701 By convention, the freely available codes are above 16 included;
702 the others are reserved.
703 The ordering of the flags can be significant. For instance: `IG{2}'
705 means ignore errors and jump two lines ahead both in case of match and
706 in case of error, while `G{2}I' means ignore errors, but jump two lines
707 ahead only in case of match.
708 More flags (mainly Action Flags) will be added as needed.
710
712 See regex(7) and/or re_format(7).
713
715 Everything starting with `%' requires substitution;
716 the only obvious exception is `%%', which is left as is;
718 the basic substitution is `%d', where `d' is a digit; 0 means the whole
720 string, while 1-9 is a submatch;
721 a `%' followed by a `{' invokes an advanced substitution. The pattern
723 is:
724 `%' `{' [ <op> ] <name> `(' <substitution> `)' `}'
726 where <name> must be a legal name for the map, i.e.
728 <name> ::= [a-z][a-z0-9]* (case insensitive)
730 <op> ::= `>' `|' `&' `&&' `*' `**' `$'
731 and <substitution> must be a legal substitution pattern, with no limits
733 on the nesting level.
734 The operators are:
736 > sub context invocation; <name> must be a legal, already defined
738 rewrite context name
739 | external command invocation; <name> must refer to a legal,
741 already defined command name (NOT IMPL.)
742 & variable assignment; <name> defines a variable in the running
744 operation structure which can be dereferenced later; operator &
745 assigns a variable in the rewrite context scope; operator &&
746 assigns a variable that scopes the entire session, e.g. its
747 value can be dereferenced later by other rewrite contexts
748 * variable dereferencing; <name> must refer to a variable that is
750 defined and assigned for the running operation; operator *
751 dereferences a variable scoping the rewrite context; operator **
752 dereferences a variable scoping the whole session, e.g. the
753 value is passed across rewrite contexts
754 $ parameter dereferencing; <name> must refer to an existing
756 parameter; the idea is to make some run-time parameters set by
757 the system available to the rewrite engine, as the client host
758 name, the bind DN if any, constant parameters initialized at
759 config time, and so on; no parameter is currently set by either
760 back-ldap or back-meta, but constant parameters can be defined
761 in the configuration file by using the rewriteParam directive.
762 Substitution escaping has been delegated to the `%' symbol, which is
764 used instead of `\' in string substitution patterns because `\' is
765 already escaped by slapd's low level parsing routines; as a
766 consequence, regex escaping requires two `\' symbols, e.g.
767 `.*\.foo\.bar' must be written as `.*\\.foo\\.bar'.
768
770 A rewrite context is a set of rules which are applied in sequence. The
771 basic idea is to have an application initialize a rewrite engine (think
772 of Apache's mod_rewrite ...) with a set of rewrite contexts; when
773 string rewriting is required, one invokes the appropriate rewrite
774 context with the input string and obtains the newly rewritten one if no
775 errors occur.
776 Each basic server operation is associated to a rewrite context; they
778 are divided in two main groups: client -> server and server -> client
779 rewriting.
780 client -> server:
782 (default) if defined and no specific context
784 is available
785 bindDN bind
786 searchBase search
787 searchFilter search
788 searchFilterAttrDN search
789 compareDN compare
790 compareAttrDN compare AVA
791 addDN add
792 addAttrDN add AVA
793 modifyDN modify
794 modifyAttrDN modify AVA
795 modrDN modrdn
796 newSuperiorDN modrdn
797 deleteDN delete
798 exopPasswdDN password modify extended operation DN if proxy
799 server -> client:
801 searchResult search (only if defined; no default;
803 acts on DN and DN-syntax attributes
804 of search results)
805 searchAttrDN search AVA
806 matchedDN all ops (only if applicable)
807
809 rewriteEngine { on | off }
810 If `on', the requested rewriting is performed; if `off', no
811 rewriting takes place (an easy way to stop rewriting without
812 altering too much the configuration file).
813 rewriteContext <context name> [ alias <aliased context name> ]
815 <Context name> is the name that identifies the context, i.e. the
816 name used by the application to refer to the set of rules it
817 contains. It is used also to reference sub contexts in string
818 rewriting. A context may alias another one. In this case the
819 alias context contains no rule, and any reference to it will
820 result in accessing the aliased one.
821 rewriteRule <regex match pattern> <substitution pattern> [ <flags> ]
823 Determines how a string can be rewritten if a pattern is
824 matched. Examples are reported below.
825
827 rewriteMap <map type> <map name> [ <map attrs> ]
828 Allows one to define a map that transforms substring rewriting
829 into something else. The map is referenced inside the
830 substitution pattern of a rule.
831 rewriteParam <param name> <param value>
833 Sets a value with global scope, that can be dereferenced by the
834 command `%{$paramName}'.
835 rewriteMaxPasses <number of passes> [<number of passes per rule>]
837 Sets the maximum number of total rewriting passes that can be
838 performed in a single rewrite operation (to avoid loops). A
839 safe default is set to 100; note that reaching this limit is
840 still treated as a success; recursive invocation of rules is
841 simply interrupted. The count applies to the rewriting
842 operation as a whole, not to any single rule; an optional per-
843 rule limit can be set. This limit is overridden by setting
844 specific per-rule limits with the `M{n}' flag.
845
847 # set to `off' to disable rewriting
848 rewriteEngine on
849 # the rules the "suffixmassage" directive implies
851 rewriteEngine on
852 # all dataflow from client to server referring to DNs
853 rewriteContext default
854 rewriteRule "(.*)<virtualnamingcontext>$" "%1<realnamingcontext>" ":"
855 # empty filter rule
856 rewriteContext searchFilter
857 # all dataflow from server to client
858 rewriteContext searchResult
859 rewriteRule "(.*)<realnamingcontext>$" "%1<virtualnamingcontext>" ":"
860 rewriteContext searchAttrDN alias searchResult
861 rewriteContext matchedDN alias searchResult
862 # Everything defined here goes into the `default' context.
864 # This rule changes the naming context of anything sent
865 # to `dc=home,dc=net' to `dc=OpenLDAP, dc=org'
866 rewriteRule "(.*)dc=home,[ ]?dc=net"
868 "%1dc=OpenLDAP, dc=org" ":"
869 # since a pretty/normalized DN does not include spaces
871 # after rdn separators, e.g. `,', this rule suffices:
872 rewriteRule "(.*)dc=home,dc=net"
874 "%1dc=OpenLDAP,dc=org" ":"
875 # Start a new context (ends input of the previous one).
877 # This rule adds blanks between DN parts if not present.
878 rewriteContext addBlanks
879 rewriteRule "(.*),([^ ].*)" "%1, %2"
880 # This one eats blanks
882 rewriteContext eatBlanks
883 rewriteRule "(.*),[ ](.*)" "%1,%2"
884 # Here control goes back to the default rewrite
886 # context; rules are appended to the existing ones.
887 # anything that gets here is piped into rule `addBlanks'
888 rewriteContext default
889 rewriteRule ".*" "%{>addBlanks(%0)}" ":"
890 # Rewrite the search base according to `default' rules.
892 rewriteContext searchBase alias default
893 # Search results with OpenLDAP DN are rewritten back with
895 # `dc=home,dc=net' naming context, with spaces eaten.
896 rewriteContext searchResult
897 rewriteRule "(.*[^ ]?)[ ]?dc=OpenLDAP,[ ]?dc=org"
898 "%{>eatBlanks(%1)}dc=home,dc=net" ":"
899 # Bind with email instead of full DN: we first need
901 # an ldap map that turns attributes into a DN (the
902 # argument used when invoking the map is appended to
903 # the URI and acts as the filter portion)
904 rewriteMap ldap attr2dn "ldap://host/dc=my,dc=org?dn?sub"
905 # Then we need to detect DN made up of a single email,
907 # e.g. `mail=someone@example.com'; note that the rule
908 # in case of match stops rewriting; in case of error,
909 # it is ignored. In case we are mapping virtual
910 # to real naming contexts, we also need to rewrite
911 # regular DNs, because the definition of a bindDn
912 # rewrite context overrides the default definition.
913 rewriteContext bindDN
914 rewriteRule "^mail=[^,]+@[^,]+$" "%{attr2dn(%0)}" ":@I"
915 # This is a rather sophisticated example. It massages a
917 # search filter in case who performs the search has
918 # administrative privileges. First we need to keep
919 # track of the bind DN of the incoming request, which is
920 # stored in a variable called `binddn' with session scope,
921 # and left in place to allow regular binding:
922 rewriteContext bindDN
923 rewriteRule ".+" "%{&&binddn(%0)}%0" ":"
924 # A search filter containing `uid=' is rewritten only
926 # if an appropriate DN is bound.
927 # To do this, in the first rule the bound DN is
928 # dereferenced, while the filter is decomposed in a
929 # prefix, in the value of the `uid=<arg>' AVA, and
930 # in a suffix. A tag `<>' is appended to the DN.
931 # If the DN refers to an entry in the `ou=admin' subtree,
932 # the filter is rewritten OR-ing the `uid=<arg>' with
933 # `cn=<arg>'; otherwise it is left as is. This could be
934 # useful, for instance, to allow apache's auth_ldap-1.4
935 # module to authenticate users with both `uid' and
936 # `cn', but only if the request comes from a possible
937 # `cn=Web auth,ou=admin,dc=home,dc=net' user.
938 rewriteContext searchFilter
939 rewriteRule "(.*\\()uid=([a-z0-9_]+)(\\).*)"
940 "%{**binddn}<>%{&prefix(%1)}%{&arg(%2)}%{&suffix(%3)}"
941 ":I"
942 rewriteRule "[^,]+,ou=admin,dc=home,dc=net"
943 "%{*prefix}|(uid=%{*arg})(cn=%{*arg})%{*suffix}" ":@I"
944 rewriteRule ".*<>" "%{*prefix}uid=%{*arg}%{*suffix}" ":"
945 # This example shows how to strip unwanted DN-valued
947 # attribute values from a search result; the first rule
948 # matches DN values below "ou=People,dc=example,dc=com";
949 # in case of match the rewriting exits successfully.
950 # The second rule matches everything else and causes
951 # the value to be rejected.
952 rewriteContext searchResult
953 rewriteRule ".*,ou=People,dc=example,dc=com" "%0" ":@"
954 rewriteRule ".*" "" "#"
955
957 In case the rewritten DN is an LDAP URI, the operation is initiated
958 towards the host[:port] indicated in the uri, if it does not refer to
959 the local server. E.g.:
960 rewriteRule '^cn=root,.*' '%0' 'G{3}'
962 rewriteRule '^cn=[a-l].*' 'ldap://ldap1.my.org/%0' ':@'
963 rewriteRule '^cn=[m-z].*' 'ldap://ldap2.my.org/%0' ':@'
964 rewriteRule '.*' 'ldap://ldap3.my.org/%0' ':@'
965 (Rule 1 is simply there to illustrate the `G{n}' action; it could have
967 been written:
968 rewriteRule '^cn=root,.*' 'ldap://ldap3.my.org/%0' ':@'
970 with the advantage of saving one rewrite pass ...)
972
975 The meta backend does not honor all ACL semantics as described in
976 slapd.access(5). In general, access checking is delegated to the
977 remote server(s). Only read (=r) access to the entry pseudo-attribute
978 and to the other attribute values of the entries returned by the search
979 operation is honored, which is performed by the frontend.
980
983 The proxy cache overlay allows caching of LDAP search requests
984 (queries) in a local database. See slapo-pcache(5) for details.
985
988 The following statements have been deprecated and should no longer be
989 used.
990 pseudorootdn <substitute DN in case of rootdn bind>
993 Use idassert-bind instead.
994 pseudorootpw <substitute password in case of rootdn bind>
997 Use idassert-bind instead.
998
1003 /etc/openldap/slapd.conf
1004 default slapd configuration file
1005
1007 slapd.conf(5), slapd-ldap(5), slapo-pcache(5), slapd(8), regex(7),
1008 re_format(7).
1009
1011 Pierangelo Masarati, based on back-ldap by Howard Chu
1012OpenLDAP 2.4.57 2021/01/18 SLAPD-META(5)