1SLAPO-RWM(5) File Formats Manual SLAPO-RWM(5)
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6 slapo-rwm - rewrite/remap overlay to slapd
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9 /etc/openldap/slapd.conf
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12 The rwm overlay to slapd(8) performs basic DN/data rewrite and object‐
13 Class/attributeType mapping. Its usage is mostly intended to provide
14 virtual views of existing data either remotely, in conjunction with the
15 proxy backend described in slapd-ldap(5), or locally, in conjunction
16 with the relay backend described in slapd-relay(5).
17 This overlay is experimental.
19
21 An important feature of the rwm overlay is the capability to map
22 objectClasses and attributeTypes from the local set (or a subset of it)
23 to a foreign set, and vice versa. This is accomplished by means of the
24 rwm-map directive.
25 rwm-map {attribute | objectclass} [<local name> | *] {<foreign name> |
27 *}
28 Map attributeTypes and objectClasses from the foreign server to
29 different values on the local slapd. The reason is that some
30 attributes might not be part of the local slapd's schema, some
31 attribute names might be different but serve the same purpose,
32 etc. If local or foreign name is `*', the name is preserved.
33 If local name is omitted, the foreign name is removed. Unmapped
34 names are preserved if both local and foreign name are `*', and
35 removed if local name is omitted and foreign name is `*'.
36 The local objectClasses and attributeTypes must be defined in the local
38 schema; the foreign ones do not have to, but users are encouraged to
39 explicitly define the remote attributeTypes and the objectClasses they
40 intend to map. All in all, when remapping a remote server via back-
41 ldap (slapd-ldap(5)) or back-meta (slapd-meta(5)) their definition can
42 be easily obtained by querying the subschemaSubentry of the remote
43 server; the problem should not exist when remapping a local database.
44 Note, however, that the decision whether to rewrite or not attribute‐
45 Types with distinguishedName syntax, requires the knowledge of the
46 attributeType syntax. See the REWRITING section for details.
47 Note that when mapping DN-valued attributes from local to remote, first
49 the DN is rewritten, and then the attributeType is mapped; while map‐
50 ping from remote to local, first the attributeType is mapped, and then
51 the DN is rewritten. As such, it is important that the local
52 attributeType is appropriately defined as using the distinguishedName
53 syntax. Also, note that there are DN-related syntaxes (i.e. compound
54 types with a portion that is DN-valued), like nameAndOptionalUID, whose
55 values are currently not rewritten.
56 If the foreign type of an attribute mapping is not defined on the local
58 server, it might be desirable to have the attribute values normalized
59 after the mapping process. Not normalizing the values can lead to wrong
60 results, when the rwm overlay is used together with e.g. the pcache
61 overlay. This normalization can be enabled by means of the rwm-normal‐
62 ize-mapped-attrs directive.
63 rwm-normalize-mapped-attrs {yes|no}
65 Set this to "yes", if the rwm overlay should try to normalize
66 the values of attributes that are mapped from an attribute type
67 that is unknown to the local server. The default value of this
68 setting is "no".
69 rwm-drop-unrequested-attrs {yes|no}
71 Set this to "yes", if the rwm overlay should drop attributes
72 that are not explicitly requested by a search operation. When
73 this is set to "no", the rwm overlay will leave all attributes
74 in place, so that subsequent modules can further manipulate
75 them. In any case, unrequested attributes will be omitted from
76 search results by the frontend, when the search entry response
77 package is encoded. The default value of this setting is "yes".
78
80 A basic feature of the rwm overlay is the capability to perform suffix
81 massaging between a virtual and a real naming context by means of the
82 rwm-suffixmassage directive. This, in conjunction with proxy backends,
83 slapd-ldap(5) and slapd-meta(5), or with the relay backend,
84 slapd-relay(5), allows one to create virtual views of databases. A
85 distinguishing feature of this overlay is that, when instantiated
86 before any database, it can modify the DN of requests before database
87 selection. For this reason, rules that rewrite the empty DN ("") or
88 the subschemaSubentry DN (usually "cn=subschema"), would prevent
89 clients from reading the root DSE or the DSA's schema.
90 rwm-suffixmassage [<virtual naming context>] <real naming context>
92 Shortcut to implement naming context rewriting; the trailing
93 part of the DN is rewritten from the virtual to the real naming
94 context in the bindDN, searchDN, searchFilterAttrDN, compareDN,
95 compareAttrDN, addDN, addAttrDN, modifyDN, modifyAttrDN, modrDN,
96 newSuperiorDN, deleteDN, exopPasswdDN, and from the real to the
97 virtual naming context in the searchEntryDN, searchAttrDN and
98 matchedDN rewrite contexts. By default no rewriting occurs for
99 the searchFilter and for the referralAttrDN and referralDN re‐
100 write contexts. If no <virtual naming context> is given, the
101 first suffix of the database is used; this requires the rwm-suf‐
102 fixmassage directive be defined after the database suffix direc‐
103 tive. The rwm-suffixmassage directive automatically sets the
104 rwm-rewriteEngine to ON.
105 See the REWRITING section for details.
107
109 A string is rewritten according to a set of rules, called a `rewrite
110 context'. The rules are based on POSIX (''extended'') regular expres‐
111 sions with substring matching; basic variable substitution and map res‐
112 olution of substrings is allowed by specific mechanisms detailed in the
113 following. The behavior of pattern matching/substitution can be
114 altered by a set of flags.
115 <rewrite context> ::= <rewrite rule> [...]
117 <rewrite rule> ::= <pattern> <action> [<flags>]
118 The underlying concept is to build a lightweight rewrite module for the
120 slapd server (initially dedicated to the LDAP backend):
121
123 An incoming string is matched against a set of rewriteRules. Rules are
124 made of a regex match pattern, a substitution pattern and a set of
125 actions, described by a set of optional flags. In case of match,
126 string rewriting is performed according to the substitution pattern
127 that allows one to refer to substrings matched in the incoming string.
128 The actions, if any, are finally performed. Each rule is executed
129 recursively, unless altered by specific action flags; see "Action
130 Flags" for details. A default limit on the recursion level is set, and
131 can be altered by the rwm-rewriteMaxPasses directive, as detailed in
132 the "Additional Configuration Syntax" section. The substitution pat‐
133 tern allows map resolution of substrings. A map is a generic object
134 that maps a substitution pattern to a value. The flags are divided in
135 "Pattern Matching Flags" and "Action Flags"; the former alter the regex
136 match pattern behavior, while the latter alter the actions that are
137 taken after substitution.
138
140 `C' honors case in matching (default is case insensitive)
141 `R' use POSIX ''basic'' regular expressions (default is
143 ''extended'')
144 `M{n}' allow no more than n recursive passes for a specific rule; does
146 not alter the max total count of passes, so it can only enforce
147 a stricter limit for a specific rule.
148
150 `:' apply the rule once only (default is recursive)
151 `@' stop applying rules in case of match; the current rule is still
153 applied recursively; combine with `:' to apply the current rule
154 only once and then stop.
155 `#' stop current operation if the rule matches, and issue an
157 `unwilling to perform' error.
158 `G{n}' jump n rules back and forth (watch for loops!). Note that
160 `G{1}' is implicit in every rule.
161 `I' ignores errors in rule; this means, in case of error, e.g.
163 issued by a map, the error is treated as a missed match. The
164 `unwilling to perform' is not overridden.
165 `U{n}' uses n as return code if the rule matches; the flag does not
167 alter the recursive behavior of the rule, so, to have it per‐
168 formed only once, it must be used in combination with `:', e.g.
169 `:U{32}' returns the value `32' (indicating noSuchObject) after
170 exactly one execution of the rule, if the pattern matches. As a
171 consequence, its behavior is equivalent to `@', with the return
172 code set to n; or, in other words, `@' is equivalent to `U{0}'.
173 Positive errors are allowed, indicating the related LDAP error
174 codes as specified in draft-ietf-ldapbis-protocol.
175 The ordering of the flags can be significant. For instance: `IG{2}'
177 means ignore errors and jump two lines ahead both in case of match and
178 in case of error, while `G{2}I' means ignore errors, but jump two lines
179 ahead only in case of match.
180 More flags (mainly Action Flags) will be added as needed.
182
184 See regex(7) and/or re_format(7).
185
187 Everything starting with `$' requires substitution;
188 the only obvious exception is `$$', which is turned into a single `$';
190 the basic substitution is `$<d>', where `<d>' is a digit; 0 means the
192 whole string, while 1-9 is a submatch, as discussed in regex(7) and/or
193 re_format(7).
194 a `$' followed by a `{' invokes an advanced substitution. The pattern
196 is:
197 `$' `{' [ <operator> ] <name> `(' <substitution> `)' `}'
199 where <name> must be a legal name for the map, i.e.
201 <name> ::= [a-z][a-z0-9]* (case insensitive)
203 <operator> ::= `>' `|' `&' `&&' `*' `**' `$'
204 and <substitution> must be a legal substitution pattern, with no limits
206 on the nesting level.
207 The operators are:
209 > sub-context invocation; <name> must be a legal, already defined
211 rewrite context name
212 | external command invocation; <name> must refer to a legal,
214 already defined command name (NOT IMPLEMENTED YET)
215 & variable assignment; <name> defines a variable in the running
217 operation structure which can be dereferenced later; operator &
218 assigns a variable in the rewrite context scope; operator &&
219 assigns a variable that scopes the entire session, e.g. its
220 value can be dereferenced later by other rewrite contexts
221 * variable dereferencing; <name> must refer to a variable that is
223 defined and assigned for the running operation; operator *
224 dereferences a variable scoping the rewrite context; operator **
225 dereferences a variable scoping the whole session, e.g. the
226 value is passed across rewrite contexts
227 $ parameter dereferencing; <name> must refer to an existing param‐
229 eter; the idea is to make some run-time parameters set by the
230 system available to the rewrite engine, as the client host name,
231 the bind DN if any, constant parameters initialized at config
232 time, and so on; no parameter is currently set by either
233 back-ldap or back-meta, but constant parameters can be defined
234 in the configuration file by using the rewriteParam directive.
235 Substitution escaping has been delegated to the `$' symbol, which is
237 used instead of `\' in string substitution patterns because `\' is
238 already escaped by slapd's low level parsing routines; as a conse‐
239 quence, regex escaping requires two `\' symbols, e.g. `.*\.foo\.bar'
240 must be written as `.*\\.foo\\.bar'.
241
243 A rewrite context is a set of rules which are applied in sequence. The
244 basic idea is to have an application initialize a rewrite engine (think
245 of Apache's mod_rewrite ...) with a set of rewrite contexts; when
246 string rewriting is required, one invokes the appropriate rewrite con‐
247 text with the input string and obtains the newly rewritten one if no
248 errors occur.
249 Each basic server operation is associated to a rewrite context; they
251 are divided in two main groups: client -> server and server -> client
252 rewriting.
253 client -> server:
255 (default) if defined and no specific context
257 is available
258 bindDN bind
259 searchDN search
260 searchFilter search
261 searchFilterAttrDN search
262 compareDN compare
263 compareAttrDN compare AVA
264 addDN add
265 addAttrDN add AVA (DN portion of "ref" excluded)
266 modifyDN modify
267 modifyAttrDN modify AVA (DN portion of "ref" excluded)
268 referralAttrDN add/modify DN portion of referrals
269 (default to none)
270 renameDN modrdn (the old DN)
271 newSuperiorDN modrdn (the new parent DN, if any)
272 newRDN modrdn (the new relative DN)
273 deleteDN delete
274 exopPasswdDN password modify extended operation DN
275 server -> client:
277 searchEntryDN search (only if defined; no default;
279 acts on DN of search entries)
280 searchAttrDN search AVA (only if defined; defaults
281 to searchEntryDN; acts on DN-syntax
282 attributes of search results)
283 matchedDN all ops (only if applicable; defaults
284 to searchEntryDN)
285 referralDN all ops (only if applicable; defaults
286 to none)
287
289 All rewrite/remap directives start with the prefix rwm-; for backwards
290 compatibility with the historical slapd-ldap(5) and slapd-meta(5)
291 builtin rewrite/remap capabilities, the prefix may be omitted, but this
292 practice is strongly discouraged.
293 rwm-rewriteEngine { on | off }
295 If `on', the requested rewriting is performed; if `off', no
296 rewriting takes place (an easy way to stop rewriting without
297 altering too much the configuration file).
298 rwm-rewriteContext <context name> [ alias <aliased context name> ]
300 <Context name> is the name that identifies the context, i.e. the
301 name used by the application to refer to the set of rules it
302 contains. It is used also to reference sub contexts in string
303 rewriting. A context may alias another one. In this case the
304 alias context contains no rule, and any reference to it will
305 result in accessing the aliased one.
306 rwm-rewriteRule <regex match pattern> <substitution pattern> [ <flags>
308 ]
309 Determines how a string can be rewritten if a pattern is
310 matched. Examples are reported below.
311
313 rwm-rewriteMap <map type> <map name> [ <map attrs> ]
314 Allows one to define a map that transforms substring rewriting
315 into something else. The map is referenced inside the substitu‐
316 tion pattern of a rule.
317 rwm-rewriteParam <param name> <param value>
319 Sets a value with global scope, that can be dereferenced by the
320 command `${$paramName}'.
321 rwm-rewriteMaxPasses <number of passes> [<number of passes per rule>]
323 Sets the maximum number of total rewriting passes that can be
324 performed in a single rewrite operation (to avoid loops). A
325 safe default is set to 100; note that reaching this limit is
326 still treated as a success; recursive invocation of rules is
327 simply interrupted. The count applies to the rewriting opera‐
328 tion as a whole, not to any single rule; an optional per-rule
329 limit can be set. This limit is overridden by setting specific
330 per-rule limits with the `M{n}' flag.
331
334 Currently, few maps are builtin but additional map types may be regis‐
335 tered at runtime.
336 Supported maps are:
338 LDAP <URI> [bindwhen=<when>] [version=<version>] [binddn=<DN>] [creden‐
340 tials=<cred>]
341 The LDAP map expands a value by performing a simple LDAP search.
342 Its configuration is based on a mandatory URI, whose attrs por‐
343 tion must contain exactly one attribute (use entryDN to fetch
344 the DN of an entry). If a multi-valued attribute is used, only
345 the first value is considered.
346 The parameter bindwhen determines when the connection is estab‐
348 lished. It can take the values now, later, and everytime,
349 respectively indicating that the connection should be created at
350 startup, when required, or any time it is used. In the former
351 two cases, the connection is cached, while in the latter a fresh
352 new one is used all times. This is the default.
353 The parameters binddn and credentials represent the DN and the
355 password that is used to perform an authenticated simple bind
356 before performing the search operation; if not given, an anony‐
357 mous connection is used.
358 The parameter version can be 2 or 3 to indicate the protocol
360 version that must be used. The default is 3.
361 slapd <URI>
364 The slapd map expands a value by performing an internal LDAP
365 search. Its configuration is based on a mandatory URI, which
366 must begin with ldap:/// (i.e., it must be an LDAP URI and it
367 must not specify a host). As with the LDAP map, the attrs por‐
368 tion must contain exactly one attribute, and if a multi-valued
369 attribute is used, only the first value is considered.
370
373 # set to `off' to disable rewriting
374 rwm-rewriteEngine on
375 # the rules the "suffixmassage" directive implies
377 rwm-rewriteEngine on
378 # all dataflow from client to server referring to DNs
379 rwm-rewriteContext default
380 rwm-rewriteRule "(.+,)?<virtualnamingcontext>$" "$1<realnamingcontext>" ":"
381 # empty filter rule
382 rwm-rewriteContext searchFilter
383 # all dataflow from server to client
384 rwm-rewriteContext searchEntryDN
385 rwm-rewriteRule "(.+,)?<realnamingcontext>$" "$1<virtualnamingcontext>" ":"
386 rwm-rewriteContext searchAttrDN alias searchEntryDN
387 rwm-rewriteContext matchedDN alias searchEntryDN
388 # misc empty rules
389 rwm-rewriteContext referralAttrDN
390 rwm-rewriteContext referralDN
391 # Everything defined here goes into the `default' context.
393 # This rule changes the naming context of anything sent
394 # to `dc=home,dc=net' to `dc=OpenLDAP, dc=org'
395 rwm-rewriteRule "(.+,)?dc=home,[ ]?dc=net$"
397 "$1dc=OpenLDAP, dc=org" ":"
398 # since a pretty/normalized DN does not include spaces
400 # after rdn separators, e.g. `,', this rule suffices:
401 rwm-rewriteRule "(.+,)?dc=home,dc=net$"
403 "$1dc=OpenLDAP,dc=org" ":"
404 # Start a new context (ends input of the previous one).
406 # This rule adds blanks between DN parts if not present.
407 rwm-rewriteContext addBlanks
408 rwm-rewriteRule "(.*),([^ ].*)" "$1, $2"
409 # This one eats blanks
411 rwm-rewriteContext eatBlanks
412 rwm-rewriteRule "(.*), (.*)" "$1,$2"
413 # Here control goes back to the default rewrite
415 # context; rules are appended to the existing ones.
416 # anything that gets here is piped into rule `addBlanks'
417 rwm-rewriteContext default
418 rwm-rewriteRule ".*" "${>addBlanks($0)}" ":"
419 # Rewrite the search base according to `default' rules.
421 rwm-rewriteContext searchDN alias default
422 # Search results with OpenLDAP DN are rewritten back with
424 # `dc=home,dc=net' naming context, with spaces eaten.
425 rwm-rewriteContext searchEntryDN
426 rwm-rewriteRule "(.*[^ ],)?[ ]?dc=OpenLDAP,[ ]?dc=org$"
427 "${>eatBlanks($1)}dc=home,dc=net" ":"
428 # Bind with email instead of full DN: we first need
430 # an ldap map that turns attributes into a DN (the
431 # argument used when invoking the map is appended to
432 # the URI and acts as the filter portion)
433 rwm-rewriteMap ldap attr2dn "ldap://host/dc=my,dc=org?dn?sub"
434 # Then we need to detect DN made up of a single email,
436 # e.g. `mail=someone@example.com'; note that the rule
437 # in case of match stops rewriting; in case of error,
438 # it is ignored. In case we are mapping virtual
439 # to real naming contexts, we also need to rewrite
440 # regular DNs, because the definition of a bindDN
441 # rewrite context overrides the default definition.
442 rwm-rewriteContext bindDN
443 rwm-rewriteRule "^mail=[^,]+@[^,]+$" "${attr2dn($0)}" ":@I"
444 # This is a rather sophisticated example. It massages a
446 # search filter in case who performs the search has
447 # administrative privileges. First we need to keep
448 # track of the bind DN of the incoming request, which is
449 # stored in a variable called `binddn' with session scope,
450 # and left in place to allow regular binding:
451 rwm-rewriteContext bindDN
452 rwm-rewriteRule ".+" "${&&binddn($0)}$0" ":"
453 # A search filter containing `uid=' is rewritten only
455 # if an appropriate DN is bound.
456 # To do this, in the first rule the bound DN is
457 # dereferenced, while the filter is decomposed in a
458 # prefix, in the value of the `uid=<arg>' AVA, and
459 # in a suffix. A tag `<>' is appended to the DN.
460 # If the DN refers to an entry in the `ou=admin' subtree,
461 # the filter is rewritten OR-ing the `uid=<arg>' with
462 # `cn=<arg>'; otherwise it is left as is. This could be
463 # useful, for instance, to allow apache's auth_ldap-1.4
464 # module to authenticate users with both `uid' and
465 # `cn', but only if the request comes from a possible
466 # `cn=Web auth,ou=admin,dc=home,dc=net' user.
467 rwm-rewriteContext searchFilter
468 rwm-rewriteRule "(.*\\()uid=([a-z0-9_]+)(\\).*)"
469 "${**binddn}<>${&prefix($1)}${&arg($2)}${&suffix($3)}"
470 ":I"
471 rwm-rewriteRule "^[^,]+,ou=admin,dc=home,dc=net$"
472 "${*prefix}|(uid=${*arg})(cn=${*arg})${*suffix}" ":@I"
473 rwm-rewriteRule ".*<>$" "${*prefix}uid=${*arg}${*suffix}" ":"
474 # This example shows how to strip unwanted DN-valued
476 # attribute values from a search result; the first rule
477 # matches DN values below "ou=People,dc=example,dc=com";
478 # in case of match the rewriting exits successfully.
479 # The second rule matches everything else and causes
480 # the value to be rejected.
481 rwm-rewriteContext searchEntryDN
482 rwm-rewriteRule ".+,ou=People,dc=example,dc=com$" "$0" ":@"
483 rwm-rewriteRule ".*" "" "#"
484
486 The following directives map the object class `groupOfNames' to the
487 object class `groupOfUniqueNames' and the attribute type `member' to
488 the attribute type `uniqueMember':
489 map objectclass groupOfNames groupOfUniqueNames
491 map attribute uniqueMember member
492 This presents a limited attribute set from the foreign server:
494 map attribute cn *
496 map attribute sn *
497 map attribute manager *
498 map attribute description *
499 map attribute *
500 These lines map cn, sn, manager, and description to themselves, and any
502 other attribute gets "removed" from the object before it is sent to the
503 client (or sent up to the LDAP server). This is obviously a simplistic
504 example, but you get the point.
505
507 /etc/openldap/slapd.conf
508 default slapd configuration file
509
511 slapd.conf(5), slapd-config(5), slapd-ldap(5), slapd-meta(5),
512 slapd-relay(5), slapd(8), regex(7), re_format(7).
513
515 Pierangelo Masarati; based on back-ldap rewrite/remap features by
516 Howard Chu, Pierangelo Masarati.
517OpenLDAP 2.4.47 2018/12/19 SLAPO-RWM(5)