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
22 intended 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
60 attributes related to entry creation and modification should not be
61 proxied, as they could be mistakenly written to the target server(s),
62 generating an error. The current implementation automatically sets
63 lastmod 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
93 selection 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
101 error 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
135 directive.
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
149 instead 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
160 remembered for rebinds, when trying to re-establish a broken
161 connection, or when chasing a referral, if chase-referrals is
162 set 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"
201 directive. 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 client-pr {accept-unsolicited|DISABLE|<size>}
252 This feature allows one to use RFC 2696 Paged Results control
253 when performing search operations with a specific target, irre‐
254 spective of the client's request. When set to a numeric value,
255 Paged Results control is always used with size as the page size.
256 When set to accept-unsolicited, unsolicited Paged Results con‐
257 trol responses are accepted and honored for compatibility with
258 broken remote DSAs. The client is not exposed to paged results
259 handling between slapd-meta(5) and the remote servers. By
260 default (disabled), Paged Results control is not used and
261 responses are not accepted. If set before any target specifica‐
262 tion, it affects all targets, unless overridden by any per-tar‐
263 get directive.
264 default-target [<target>]
267 The "default-target" directive can also be used during target
268 specification. With no arguments it marks the current target as
269 the default. The optional number marks target <target> as the
270 default one, starting from 1. Target <target> must be defined.
271 filter <pattern>
274 This directive allows specifying a regex(5) pattern to indicate
275 what search filter terms are actually served by a target.
276 In a search request, if the search filter matches the pattern
278 the target is considered while fulfilling the request; otherwise
279 the target is ignored. There may be multiple occurrences of the
280 filter directive for each target.
281 idassert-authzFrom <authz-regexp>
284 if defined, selects what local identities are authorized to
285 exploit the identity assertion feature. The string <authz-reg‐
286 exp> follows the rules defined for the authzFrom attribute. See
287 slapd.conf(5), section related to authz-policy, for details on
288 the syntax of this field.
289 idassert-bind bindmethod=none|simple|sasl [binddn=<simple DN>]
292 [credentials=<simple password>] [saslmech=<SASL mech>]
293 [secprops=<properties>] [realm=<realm>] [authcId=<authentication
294 ID>] [authzId=<authorization ID>] [authz={native|proxyauthz}]
295 [mode=<mode>] [flags=<flags>] [starttls=no|yes|critical]
296 [tls_cert=<file>] [tls_key=<file>] [tls_cacert=<file>]
297 [tls_cacertdir=<path>] [tls_reqcert=never|allow|try|demand]
298 [tls_cipher_suite=<ciphers>]
299 [tls_protocol_min=<major>[.<minor>]]
300 [tls_crlcheck=none|peer|all]
301 Allows one to define the parameters of the authentication method
302 that is internally used by the proxy to authorize connections
303 that are authenticated by other databases. The identity defined
304 by this directive, according to the properties associated to the
305 authentication method, is supposed to have auth access on the
306 target server to attributes used on the proxy for authentication
307 and authorization, and to be allowed to authorize the users.
308 This requires to have proxyAuthz privileges on a wide set of
309 DNs, e.g. authzTo=dn.subtree:"", and the remote server to have
310 authz-policy set to to or both. See slapd.conf(5) for details
311 on these statements and for remarks and drawbacks about their
312 usage. The supported bindmethods are
313 none|simple|sasl
315 where none is the default, i.e. no identity assertion is
317 performed.
318 The authz parameter is used to instruct the SASL bind to exploit
320 native SASL authorization, if available; since connections are
321 cached, this should only be used when authorizing with a fixed
322 identity (e.g. by means of the authzDN or authzID parameters).
323 Otherwise, the default proxyauthz is used, i.e. the proxyAuthz
324 control (Proxied Authorization, RFC 4370) is added to all
325 operations.
326 The supported modes are:
328 <mode> := {legacy|anonymous|none|self}
330 If <mode> is not present, and authzId is given, the proxy always
332 authorizes that identity. <authorization ID> can be
333 u:<user>
335 [dn:]<DN>
337 The former is supposed to be expanded by the remote server
339 according to the authz rules; see slapd.conf(5) for details. In
340 the latter case, whether or not the dn: prefix is present, the
341 string must pass DN validation and normalization.
342 The default mode is legacy, which implies that the proxy will
344 either perform a simple bind as the authcDN or a SASL bind as
345 the authcID and assert the client's identity when it is not
346 anonymous. Direct binds are always proxied. The other modes
347 imply that the proxy will always either perform a simple bind as
348 the authcDN or a SASL bind as the authcID, unless restricted by
349 idassert-authzFrom rules (see below), in which case the
350 operation will fail; eventually, it will assert some other
351 identity according to <mode>. Other identity assertion modes
352 are anonymous and self, which respectively mean that the empty
353 or the client's identity will be asserted; none, which means
354 that no proxyAuthz control will be used, so the authcDN or the
355 authcID identity will be asserted. For all modes that require
356 the use of the proxyAuthz control, on the remote server the
357 proxy identity must have appropriate authzTo permissions, or the
358 asserted identities must have appropriate authzFrom permissions.
359 Note, however, that the ID assertion feature is mostly useful
360 when the asserted identities do not exist on the remote server.
361 Flags can be
363 override,[non-]prescriptive,proxy-authz-[non-]critical
365 When the override flag is used, identity assertion takes place
367 even when the database is authorizing for the identity of the
368 client, i.e. after binding with the provided identity, and thus
369 authenticating it, the proxy performs the identity assertion
370 using the configured identity and authentication method.
371 When the prescriptive flag is used (the default), operations
373 fail with inappropriateAuthentication for those identities whose
374 assertion is not allowed by the idassert-authzFrom patterns. If
375 the non-prescriptive flag is used, operations are performed
376 anonymously for those identities whose assertion is not allowed
377 by the idassert-authzFrom patterns.
378 When the proxy-authz-non-critical flag is used (the default),
380 the proxyAuthz control is not marked as critical, in violation
381 of RFC 4370. Use of proxy-authz-critical is recommended.
382 The TLS settings default to the same as the main slapd TLS
384 settings, except for tls_reqcert which defaults to "demand".
385 The identity associated to this directive is also used for
387 privileged operations whenever idassert-bind is defined and
388 acl-bind is not. See acl-bind for details.
389 idle-timeout <time>
392 This directive causes a cached connection to be dropped an
393 recreated after it has been idle for the specified time. The
394 value can be specified as
395 [<d>d][<h>h][<m>m][<s>[s]]
397 where <d>, <h>, <m> and <s> are respectively treated as days,
399 hours, minutes and seconds. If set before any target
400 specification, it affects all targets, unless overridden by any
401 per-target directive.
402 keepalive <idle>:<probes>:<interval>
405 The keepalive parameter sets the values of idle, probes, and
406 interval used to check whether a socket is alive; idle is the
407 number of seconds a connection needs to remain idle before TCP
408 starts sending keepalive probes; probes is the maximum number of
409 keepalive probes TCP should send before dropping the connection;
410 interval is interval in seconds between individual keepalive
411 probes. Only some systems support the customization of these
412 values; the keepalive parameter is ignored otherwise, and
413 system-wide settings are used.
414 map {attribute|objectclass} [<local name>|*] {<foreign name>|*}
417 This maps object classes and attributes as in the LDAP backend.
418 See slapd-ldap(5).
419 network-timeout <time>
422 Sets the network timeout value after which poll(2)/select(2)
423 following a connect(2) returns in case of no activity. The
424 value is in seconds, and it can be specified as for
425 idle-timeout. If set before any target specification, it
426 affects all targets, unless overridden by any per-target
427 directive.
428 nretries {forever|never|<nretries>}
431 This directive defines how many times a bind should be retried
432 in case of temporary failure in contacting a target. If defined
433 before any target specification, it applies to all targets (by
434 default, 3 times); the global value can be overridden by
435 redefinitions inside each target specification.
436 rewrite* ...
439 The rewrite options are described in the "REWRITING" section.
440 subtree-{exclude|include} <rule>
443 This directive allows one to indicate what subtrees are actually
444 served by a target. The syntax of the supported rules is
445 <rule>: [dn[.<style>]:]<pattern>
447 <style>: subtree|children|regex
449 When <style> is either subtree or children the <pattern> is a DN
451 that must be within the naming context served by the target.
452 When <style> is regex the <pattern> is a regex(5) pattern. If
453 the dn.<style>: prefix is omitted, dn.subtree: is implicitly
454 assumed for backward compatibility.
455 In the subtree-exclude form if the request DN matches at least
457 one rule, the target is not considered while fulfilling the
458 request; otherwise, the target is considered based on the value
459 of the request DN. When the request is a search, also the scope
460 is considered.
461 In the subtree-include form if the request DN matches at least
463 one rule, the target is considered while fulfilling the request;
464 otherwise the target is ignored.
465 | match | exclude |
468 +---------+---------+-------------------+
469 | T | T | not candidate |
470 | F | T | continue checking |
471 +---------+---------+-------------------+
472 | T | F | candidate |
473 | F | F | not candidate |
474 +---------+---------+-------------------+
475 There may be multiple occurrences of the subtree-exclude or
477 subtree-include directive for each of the targets, but they are
478 mutually exclusive.
479 suffixmassage <virtual naming context> <real naming context>
482 All the directives starting with "rewrite" refer to the rewrite
483 engine that has been added to slapd. The "suffixmassage"
484 directive was introduced in the LDAP backend to allow suffix
485 massaging while proxying. It has been obsoleted by the
486 rewriting tools. However, both for backward compatibility and
487 for ease of configuration when simple suffix massage is
488 required, it has been preserved. It wraps the basic rewriting
489 instructions that perform suffix massaging. See the "REWRITING"
490 section for a detailed list of the rewrite rules it implies.
491 t-f-support {NO|yes|discover}
494 enable if the remote server supports absolute filters (see RFC
495 4526 for details). If set to discover, support is detected by
496 reading the remote server's root DSE. If set before any target
497 specification, it affects all targets, unless overridden by any
498 per-target directive.
499 timeout [<op>=]<val> [...]
502 This directive allows one to set per-operation timeouts.
503 Operations can be
504 <op> ::= bind, add, delete, modrdn, modify, compare, search
506 The overall duration of the search operation is controlled
508 either by the timelimit parameter or by server-side enforced
509 time limits (see timelimit and limits in slapd.conf(5) for
510 details). This timeout parameter controls how long the target
511 can be irresponsive before the operation is aborted. Timeout is
512 meaningless for the remaining operations, unbind and abandon,
513 which do not imply any response, while it is not yet implemented
514 in currently supported extended operations. If no operation is
515 specified, the timeout val affects all supported operations. If
516 specified before any target definition, it affects all targets
517 unless overridden by per-target directives.
518 Note: if the timeout is exceeded, the operation is cancelled
520 (according to the cancel directive); the protocol does not
521 provide any means to rollback operations, so the client will not
522 be notified about the result of the operation, which may
523 eventually succeeded or not. In case the timeout is exceeded
524 during a bind operation, the connection is destroyed, according
525 to RFC4511.
526 tls {[try-]start|[try-]propagate}
529 execute the StartTLS extended operation when the connection is
530 initialized; only works if the URI directive protocol scheme is
531 not ldaps://. propagate issues the StartTLS operation only if
532 the original connection did. The try- prefix instructs the
533 proxy to continue operations if the StartTLS operation failed;
534 its use is highly deprecated. If set before any target
535 specification, it affects all targets, unless overridden by any
536 per-target directive.
537
540 A powerful (and in some sense dangerous) rewrite engine has been added
541 to both the LDAP and Meta backends. While the former can gain limited
542 beneficial effects from rewriting stuff, the latter can become an
543 amazingly powerful tool.
544 Consider a couple of scenarios first.
546 1) Two directory servers share two levels of naming context; say
548 "dc=a,dc=foo,dc=com" and "dc=b,dc=foo,dc=com". Then, an unambiguous
549 Meta database can be configured as:
550 database meta
552 suffix "dc=foo,dc=com"
553 uri "ldap://a.foo.com/dc=a,dc=foo,dc=com"
554 uri "ldap://b.foo.com/dc=b,dc=foo,dc=com"
555 Operations directed to a specific target can be easily resolved because
557 there are no ambiguities. The only operation that may resolve to
558 multiple targets is a search with base "dc=foo,dc=com" and scope at
559 least "one", which results in spawning two searches to the targets.
560 2a) Two directory servers don't share any portion of naming context,
562 but they'd present as a single DIT [Caveat: uniqueness of (massaged)
563 entries among the two servers is assumed; integrity checks risk to
564 incur in excessive overhead and have not been implemented]. Say we
565 have "dc=bar,dc=org" and "o=Foo,c=US", and we'd like them to appear as
566 branches of "dc=foo,dc=com", say "dc=a,dc=foo,dc=com" and
567 "dc=b,dc=foo,dc=com". Then we need to configure our Meta backend as:
568 database meta
570 suffix "dc=foo,dc=com"
571 uri "ldap://a.bar.com/dc=a,dc=foo,dc=com"
573 suffixmassage "dc=a,dc=foo,dc=com" "dc=bar,dc=org"
574 uri "ldap://b.foo.com/dc=b,dc=foo,dc=com"
576 suffixmassage "dc=b,dc=foo,dc=com" "o=Foo,c=US"
577 Again, operations can be resolved without ambiguity, although some
579 rewriting is required. Notice that the virtual naming context of each
580 target is a branch of the database's naming context; it is rewritten
581 back and forth when operations are performed towards the target
582 servers. What "back and forth" means will be clarified later.
583 When a search with base "dc=foo,dc=com" is attempted, if the scope is
585 "base" it fails with "no such object"; in fact, the common root of the
586 two targets (prior to massaging) does not exist. If the scope is
587 "one", both targets are contacted with the base replaced by each
588 target's base; the scope is derated to "base". In general, a scope
589 "one" search is honored, and the scope is derated, only when the
590 incoming base is at most one level lower of a target's naming context
591 (prior to massaging).
592 Finally, if the scope is "sub" the incoming base is replaced by each
594 target's unmassaged naming context, and the scope is not altered.
595 2b) Consider the above reported scenario with the two servers sharing
597 the same naming context:
598 database meta
600 suffix "dc=foo,dc=com"
601 uri "ldap://a.bar.com/dc=foo,dc=com"
603 suffixmassage "dc=foo,dc=com" "dc=bar,dc=org"
604 uri "ldap://b.foo.com/dc=foo,dc=com"
606 suffixmassage "dc=foo,dc=com" "o=Foo,c=US"
607 All the previous considerations hold, except that now there is no way
609 to unambiguously resolve a DN. In this case, all the operations that
610 require an unambiguous target selection will fail unless the DN is
611 already cached or a default target has been set. Practical
612 configurations may result as a combination of all the above scenarios.
613
615 Note on ACLs: at present you may add whatever ACL rule you desire to
616 the Meta (and LDAP) backends. However, the meaning of an ACL on a
617 proxy may require some considerations. Two philosophies may be
618 considered:
619 a) the remote server dictates the permissions; the proxy simply passes
621 back what it gets from the remote server.
622 b) the remote server unveils "everything"; the proxy is responsible for
624 protecting data from unauthorized access.
625 Of course the latter sounds unreasonable, but it is not. It is
627 possible to imagine scenarios in which a remote host discloses data
628 that can be considered "public" inside an intranet, and a proxy that
629 connects it to the internet may impose additional constraints. To this
630 purpose, the proxy should be able to comply with all the ACL matching
631 criteria that the server supports. This has been achieved with regard
632 to all the criteria supported by slapd except a special subtle case
633 (please file an ITS if you can find other exceptions:
634 <http://www.openldap.org/its/>). The rule
635 access to dn="<dn>" attrs=<attr>
637 by dnattr=<dnattr> read
638 by * none
639 cannot be matched iff the attribute that is being requested, <attr>, is
641 NOT <dnattr>, and the attribute that determines membership, <dnattr>,
642 has not been requested (e.g. in a search)
643 In fact this ACL is resolved by slapd using the portion of entry it
645 retrieved from the remote server without requiring any further
646 intervention of the backend, so, if the <dnattr> attribute has not been
647 fetched, the match cannot be assessed because the attribute is not
648 present, not because no value matches the requirement!
649 Note on ACLs and attribute mapping: ACLs are applied to the mapped
651 attributes; for instance, if the attribute locally known as "foo" is
652 mapped to "bar" on a remote server, then local ACLs apply to attribute
653 "foo" and are totally unaware of its remote name. The remote server
654 will check permissions for "bar", and the local server will possibly
655 enforce additional restrictions to "foo".
656
658 A string is rewritten according to a set of rules, called a `rewrite
659 context'. The rules are based on POSIX (''extended'') regular
660 expressions (regex) with substring matching; basic variable
661 substitution and map resolution of substrings is allowed by specific
662 mechanisms detailed in the following. The behavior of pattern
663 matching/substitution can be altered by a set of flags.
664 The underlying concept is to build a lightweight rewrite module for the
666 slapd server (initially dedicated to the LDAP backend).
667
669 An incoming string is matched against a set of rules. Rules are made
670 of a regex match pattern, a substitution pattern and a set of actions,
671 described by a set of flags. In case of match a string rewriting is
672 performed according to the substitution pattern that allows one to
673 refer to substrings matched in the incoming string. The actions, if
674 any, are finally performed. The substitution pattern allows map
675 resolution of substrings. A map is a generic object that maps a
676 substitution pattern to a value. The flags are divided in "Pattern
677 matching Flags" and "Action Flags"; the former alter the regex match
678 pattern behavior while the latter alter the action that is taken after
679 substitution.
680
682 `C' honors case in matching (default is case insensitive)
683 `R' use POSIX ''basic'' regular expressions (default is
685 ''extended'')
686 `M{n}' allow no more than n recursive passes for a specific rule; does
688 not alter the max total count of passes, so it can only enforce
689 a stricter limit for a specific rule.
690
692 `:' apply the rule once only (default is recursive)
693 `@' stop applying rules in case of match; the current rule is still
695 applied recursively; combine with `:' to apply the current rule
696 only once and then stop.
697 `#' stop current operation if the rule matches, and issue an
699 `unwilling to perform' error.
700 `G{n}' jump n rules back and forth (watch for loops!). Note that
702 `G{1}' is implicit in every rule.
703 `I' ignores errors in rule; this means, in case of error, e.g.
705 issued by a map, the error is treated as a missed match. The
706 `unwilling to perform' is not overridden.
707 `U{n}' uses n as return code if the rule matches; the flag does not
709 alter the recursive behavior of the rule, so, to have it
710 performed only once, it must be used in combination with `:',
711 e.g. `:U{16}' returns the value `16' after exactly one
712 execution of the rule, if the pattern matches. As a
713 consequence, its behavior is equivalent to `@', with the return
714 code set to n; or, in other words, `@' is equivalent to `U{0}'.
715 By convention, the freely available codes are above 16 included;
716 the others are reserved.
717 The ordering of the flags can be significant. For instance: `IG{2}'
719 means ignore errors and jump two lines ahead both in case of match and
720 in case of error, while `G{2}I' means ignore errors, but jump two lines
721 ahead only in case of match.
722 More flags (mainly Action Flags) will be added as needed.
724
726 See regex(7) and/or re_format(7).
727
729 Everything starting with `%' requires substitution;
730 the only obvious exception is `%%', which is left as is;
732 the basic substitution is `%d', where `d' is a digit; 0 means the whole
734 string, while 1-9 is a submatch;
735 a `%' followed by a `{' invokes an advanced substitution. The pattern
737 is:
738 `%' `{' [ <op> ] <name> `(' <substitution> `)' `}'
740 where <name> must be a legal name for the map, i.e.
742 <name> ::= [a-z][a-z0-9]* (case insensitive)
744 <op> ::= `>' `|' `&' `&&' `*' `**' `$'
745 and <substitution> must be a legal substitution pattern, with no limits
747 on the nesting level.
748 The operators are:
750 > sub context invocation; <name> must be a legal, already defined
752 rewrite context name
753 | external command invocation; <name> must refer to a legal,
755 already defined command name (NOT IMPL.)
756 & variable assignment; <name> defines a variable in the running
758 operation structure which can be dereferenced later; operator &
759 assigns a variable in the rewrite context scope; operator &&
760 assigns a variable that scopes the entire session, e.g. its
761 value can be dereferenced later by other rewrite contexts
762 * variable dereferencing; <name> must refer to a variable that is
764 defined and assigned for the running operation; operator *
765 dereferences a variable scoping the rewrite context; operator **
766 dereferences a variable scoping the whole session, e.g. the
767 value is passed across rewrite contexts
768 $ parameter dereferencing; <name> must refer to an existing
770 parameter; the idea is to make some run-time parameters set by
771 the system available to the rewrite engine, as the client host
772 name, the bind DN if any, constant parameters initialized at
773 config time, and so on; no parameter is currently set by either
774 back-ldap or back-meta, but constant parameters can be defined
775 in the configuration file by using the rewriteParam directive.
776 Substitution escaping has been delegated to the `%' symbol, which is
778 used instead of `\' in string substitution patterns because `\' is
779 already escaped by slapd's low level parsing routines; as a
780 consequence, regex escaping requires two `\' symbols, e.g.
781 `.*\.foo\.bar' must be written as `.*\\.foo\\.bar'.
782
784 A rewrite context is a set of rules which are applied in sequence. The
785 basic idea is to have an application initialize a rewrite engine (think
786 of Apache's mod_rewrite ...) with a set of rewrite contexts; when
787 string rewriting is required, one invokes the appropriate rewrite
788 context with the input string and obtains the newly rewritten one if no
789 errors occur.
790 Each basic server operation is associated to a rewrite context; they
792 are divided in two main groups: client -> server and server -> client
793 rewriting.
794 client -> server:
796 (default) if defined and no specific context
798 is available
799 bindDN bind
800 searchBase search
801 searchFilter search
802 searchFilterAttrDN search
803 compareDN compare
804 compareAttrDN compare AVA
805 addDN add
806 addAttrDN add AVA
807 modifyDN modify
808 modifyAttrDN modify AVA
809 modrDN modrdn
810 newSuperiorDN modrdn
811 deleteDN delete
812 exopPasswdDN password modify extended operation DN if proxy
813 server -> client:
815 searchResult search (only if defined; no default;
817 acts on DN and DN-syntax attributes
818 of search results)
819 searchAttrDN search AVA
820 matchedDN all ops (only if applicable)
821
823 rewriteEngine { on | off }
824 If `on', the requested rewriting is performed; if `off', no
825 rewriting takes place (an easy way to stop rewriting without
826 altering too much the configuration file).
827 rewriteContext <context name> [ alias <aliased context name> ]
829 <Context name> is the name that identifies the context, i.e. the
830 name used by the application to refer to the set of rules it
831 contains. It is used also to reference sub contexts in string
832 rewriting. A context may alias another one. In this case the
833 alias context contains no rule, and any reference to it will
834 result in accessing the aliased one.
835 rewriteRule <regex match pattern> <substitution pattern> [ <flags> ]
837 Determines how a string can be rewritten if a pattern is
838 matched. Examples are reported below.
839
841 rewriteMap <map type> <map name> [ <map attrs> ]
842 Allows one to define a map that transforms substring rewriting
843 into something else. The map is referenced inside the
844 substitution pattern of a rule.
845 rewriteParam <param name> <param value>
847 Sets a value with global scope, that can be dereferenced by the
848 command `%{$paramName}'.
849 rewriteMaxPasses <number of passes> [<number of passes per rule>]
851 Sets the maximum number of total rewriting passes that can be
852 performed in a single rewrite operation (to avoid loops). A
853 safe default is set to 100; note that reaching this limit is
854 still treated as a success; recursive invocation of rules is
855 simply interrupted. The count applies to the rewriting
856 operation as a whole, not to any single rule; an optional per-
857 rule limit can be set. This limit is overridden by setting
858 specific per-rule limits with the `M{n}' flag.
859
861 # set to `off' to disable rewriting
862 rewriteEngine on
863 # the rules the "suffixmassage" directive implies
865 rewriteEngine on
866 # all dataflow from client to server referring to DNs
867 rewriteContext default
868 rewriteRule "(.*)<virtualnamingcontext>$" "%1<realnamingcontext>" ":"
869 # empty filter rule
870 rewriteContext searchFilter
871 # all dataflow from server to client
872 rewriteContext searchResult
873 rewriteRule "(.*)<realnamingcontext>$" "%1<virtualnamingcontext>" ":"
874 rewriteContext searchAttrDN alias searchResult
875 rewriteContext matchedDN alias searchResult
876 # Everything defined here goes into the `default' context.
878 # This rule changes the naming context of anything sent
879 # to `dc=home,dc=net' to `dc=OpenLDAP, dc=org'
880 rewriteRule "(.*)dc=home,[ ]?dc=net"
882 "%1dc=OpenLDAP, dc=org" ":"
883 # since a pretty/normalized DN does not include spaces
885 # after rdn separators, e.g. `,', this rule suffices:
886 rewriteRule "(.*)dc=home,dc=net"
888 "%1dc=OpenLDAP,dc=org" ":"
889 # Start a new context (ends input of the previous one).
891 # This rule adds blanks between DN parts if not present.
892 rewriteContext addBlanks
893 rewriteRule "(.*),([^ ].*)" "%1, %2"
894 # This one eats blanks
896 rewriteContext eatBlanks
897 rewriteRule "(.*),[ ](.*)" "%1,%2"
898 # Here control goes back to the default rewrite
900 # context; rules are appended to the existing ones.
901 # anything that gets here is piped into rule `addBlanks'
902 rewriteContext default
903 rewriteRule ".*" "%{>addBlanks(%0)}" ":"
904 # Rewrite the search base according to `default' rules.
906 rewriteContext searchBase alias default
907 # Search results with OpenLDAP DN are rewritten back with
909 # `dc=home,dc=net' naming context, with spaces eaten.
910 rewriteContext searchResult
911 rewriteRule "(.*[^ ]?)[ ]?dc=OpenLDAP,[ ]?dc=org"
912 "%{>eatBlanks(%1)}dc=home,dc=net" ":"
913 # Bind with email instead of full DN: we first need
915 # an ldap map that turns attributes into a DN (the
916 # argument used when invoking the map is appended to
917 # the URI and acts as the filter portion)
918 rewriteMap ldap attr2dn "ldap://host/dc=my,dc=org?dn?sub"
919 # Then we need to detect DN made up of a single email,
921 # e.g. `mail=someone@example.com'; note that the rule
922 # in case of match stops rewriting; in case of error,
923 # it is ignored. In case we are mapping virtual
924 # to real naming contexts, we also need to rewrite
925 # regular DNs, because the definition of a bindDn
926 # rewrite context overrides the default definition.
927 rewriteContext bindDN
928 rewriteRule "^mail=[^,]+@[^,]+$" "%{attr2dn(%0)}" ":@I"
929 # This is a rather sophisticated example. It massages a
931 # search filter in case who performs the search has
932 # administrative privileges. First we need to keep
933 # track of the bind DN of the incoming request, which is
934 # stored in a variable called `binddn' with session scope,
935 # and left in place to allow regular binding:
936 rewriteContext bindDN
937 rewriteRule ".+" "%{&&binddn(%0)}%0" ":"
938 # A search filter containing `uid=' is rewritten only
940 # if an appropriate DN is bound.
941 # To do this, in the first rule the bound DN is
942 # dereferenced, while the filter is decomposed in a
943 # prefix, in the value of the `uid=<arg>' AVA, and
944 # in a suffix. A tag `<>' is appended to the DN.
945 # If the DN refers to an entry in the `ou=admin' subtree,
946 # the filter is rewritten OR-ing the `uid=<arg>' with
947 # `cn=<arg>'; otherwise it is left as is. This could be
948 # useful, for instance, to allow apache's auth_ldap-1.4
949 # module to authenticate users with both `uid' and
950 # `cn', but only if the request comes from a possible
951 # `cn=Web auth,ou=admin,dc=home,dc=net' user.
952 rewriteContext searchFilter
953 rewriteRule "(.*\\()uid=([a-z0-9_]+)(\\).*)"
954 "%{**binddn}<>%{&prefix(%1)}%{&arg(%2)}%{&suffix(%3)}"
955 ":I"
956 rewriteRule "[^,]+,ou=admin,dc=home,dc=net"
957 "%{*prefix}|(uid=%{*arg})(cn=%{*arg})%{*suffix}" ":@I"
958 rewriteRule ".*<>" "%{*prefix}uid=%{*arg}%{*suffix}" ":"
959 # This example shows how to strip unwanted DN-valued
961 # attribute values from a search result; the first rule
962 # matches DN values below "ou=People,dc=example,dc=com";
963 # in case of match the rewriting exits successfully.
964 # The second rule matches everything else and causes
965 # the value to be rejected.
966 rewriteContext searchResult
967 rewriteRule ".*,ou=People,dc=example,dc=com" "%0" ":@"
968 rewriteRule ".*" "" "#"
969
971 In case the rewritten DN is an LDAP URI, the operation is initiated
972 towards the host[:port] indicated in the uri, if it does not refer to
973 the local server. E.g.:
974 rewriteRule '^cn=root,.*' '%0' 'G{3}'
976 rewriteRule '^cn=[a-l].*' 'ldap://ldap1.my.org/%0' ':@'
977 rewriteRule '^cn=[m-z].*' 'ldap://ldap2.my.org/%0' ':@'
978 rewriteRule '.*' 'ldap://ldap3.my.org/%0' ':@'
979 (Rule 1 is simply there to illustrate the `G{n}' action; it could have
981 been written:
982 rewriteRule '^cn=root,.*' 'ldap://ldap3.my.org/%0' ':@'
984 with the advantage of saving one rewrite pass ...)
986
989 The meta backend does not honor all ACL semantics as described in
990 slapd.access(5). In general, access checking is delegated to the
991 remote server(s). Only read (=r) access to the entry pseudo-attribute
992 and to the other attribute values of the entries returned by the search
993 operation is honored, which is performed by the frontend.
994
997 The proxy cache overlay allows caching of LDAP search requests
998 (queries) in a local database. See slapo-pcache(5) for details.
999
1002 The following statements have been deprecated and should no longer be
1003 used.
1004 pseudorootdn <substitute DN in case of rootdn bind>
1007 Use idassert-bind instead.
1008 pseudorootpw <substitute password in case of rootdn bind>
1011 Use idassert-bind instead.
1012
1017 /etc/openldap/slapd.conf
1018 default slapd configuration file
1019
1021 slapd.conf(5), slapd-ldap(5), slapo-pcache(5), slapd(8), regex(7),
1022 re_format(7).
1023
1025 Pierangelo Masarati, based on back-ldap by Howard Chu
1026OpenLDAP 2.4.46 2018/03/22 SLAPD-META(5)