slapo-rwm(5) — Linux manual page

NAME | SYNOPSIS | DESCRIPTION | MAPPING | SUFFIX MASSAGING | REWRITING | Passes | Pattern Matching Flags | Action Flags | Pattern Matching | Substitution Pattern Syntax | Rewrite Context | Basic Configuration Syntax | Additional Configuration Syntax | MAPS | REWRITE CONFIGURATION EXAMPLES | MAPPING EXAMPLES | FILES | SEE ALSO | AUTHOR | COLOPHON

SLAPO-RWM(5)                 File Formats Manual                SLAPO-RWM(5)

NAME         top

       slapo-rwm - rewrite/remap overlay to slapd

SYNOPSIS         top


DESCRIPTION         top

       The rwm overlay to slapd(8) performs basic DN/data rewrite and
       objectClass/attributeType mapping.  Its usage is mostly intended to
       provide virtual views of existing data either remotely, in
       conjunction with the proxy backend described in slapd-ldap(5), or
       locally, in conjunction with the relay backend described in

       This overlay is experimental.

MAPPING         top

       An important feature of the rwm overlay is the capability to map
       objectClasses and attributeTypes from the local set (or a subset of
       it) to a foreign set, and vice versa.  This is accomplished by means
       of the rwm-map directive.

       rwm-map {attribute | objectclass} [<local name> | *] {<foreign name>
       | *}
              Map attributeTypes and objectClasses from the foreign server
              to different values on the local slapd.  The reason is that
              some attributes might not be part of the local slapd's schema,
              some attribute names might be different but serve the same
              purpose, etc.  If local or foreign name is `*', the name is
              preserved.  If local name is omitted, the foreign name is
              removed.  Unmapped names are preserved if both local and
              foreign name are `*', and removed if local name is omitted and
              foreign name is `*'.

       The local objectClasses and attributeTypes must be defined in the
       local schema; the foreign ones do not have to, but users are
       encouraged to explicitly define the remote attributeTypes and the
       objectClasses they intend to map.  All in all, when remapping a
       remote server via back-ldap (slapd-ldap(5)) or back-meta (‐
       slapd-meta(5)) their definition can be easily obtained by querying
       the subschemaSubentry of the remote server; the problem should not
       exist when remapping a local database.  Note, however, that the
       decision whether to rewrite or not attributeTypes with
       distinguishedName syntax, requires the knowledge of the attributeType
       syntax.  See the REWRITING section for details.

       Note that when mapping DN-valued attributes from local to remote,
       first the DN is rewritten, and then the attributeType is mapped;
       while mapping from remote to local, first the attributeType is
       mapped, and then the DN is rewritten.  As such, it is important that
       the local attributeType is appropriately defined as using the
       distinguishedName syntax.  Also, note that there are DN-related
       syntaxes (i.e. compound types with a portion that is DN-valued), like
       nameAndOptionalUID, whose values are currently not rewritten.

       If the foreign type of an attribute mapping is not defined on the
       local server, it might be desirable to have the attribute values
       normalized after the mapping process. Not normalizing the values can
       lead to wrong results, when the rwm overlay is used together with
       e.g. the pcache overlay. This normalization can be enabled by means
       of the rwm-normalize-mapped-attrs directive.

       rwm-normalize-mapped-attrs {yes|no}
              Set this to "yes", if the rwm overlay should try to normalize
              the values of attributes that are mapped from an attribute
              type that is unknown to the local server. The default value of
              this setting is "no".

       rwm-drop-unrequested-attrs {yes|no}
              Set this to "yes", if the rwm overlay should drop attributes
              that are not explicitly requested by a search operation.  When
              this is set to "no", the rwm overlay will leave all attributes
              in place, so that subsequent modules can further manipulate
              them.  In any case, unrequested attributes will be omitted
              from search results by the frontend, when the search entry
              response package is encoded.  The default value of this
              setting is "yes".


       A basic feature of the rwm overlay is the capability to perform
       suffix massaging between a virtual and a real naming context by means
       of the rwm-suffixmassage directive.  This, in conjunction with proxy
       backends, slapd-ldap(5) and slapd-meta(5), or with the relay backend,
       slapd-relay(5), allows one to create virtual views of databases.  A
       distinguishing feature of this overlay is that, when instantiated
       before any database, it can modify the DN of requests before database
       selection.  For this reason, rules that rewrite the empty DN ("") or
       the subschemaSubentry DN (usually "cn=subschema"), would prevent
       clients from reading the root DSE or the DSA's schema.

       rwm-suffixmassage [<virtual naming context>] <real naming context>
              Shortcut to implement naming context rewriting; the trailing
              part of the DN is rewritten from the virtual to the real
              naming context in the bindDN, searchDN, searchFilterAttrDN,
              compareDN, compareAttrDN, addDN, addAttrDN, modifyDN,
              modifyAttrDN, modrDN, newSuperiorDN, deleteDN, exopPasswdDN,
              and from the real to the virtual naming context in the
              searchEntryDN, searchAttrDN and matchedDN rewrite contexts.
              By default no rewriting occurs for the searchFilter and for
              the referralAttrDN and referralDN rewrite contexts.  If no
              <virtual naming context> is given, the first suffix of the
              database is used; this requires the rwm-suffixmassage
              directive be defined after the database suffix directive.  The
              rwm-suffixmassage directive automatically sets the
              rwm-rewriteEngine to ON.

       See the REWRITING section for details.

REWRITING         top

       A string is rewritten according to a set of rules, called a `rewrite
       context'.  The rules are based on POSIX (''extended'') regular
       expressions with substring matching; basic variable substitution and
       map resolution of substrings is allowed by specific mechanisms
       detailed in the following.  The behavior of pattern
       matching/substitution can be altered by a set of flags.

              <rewrite context> ::= <rewrite rule> [...]
              <rewrite rule> ::= <pattern> <action> [<flags>]

       The underlying concept is to build a lightweight rewrite module for
       the slapd server (initially dedicated to the LDAP backend):

Passes         top

       An incoming string is matched against a set of rewriteRules.  Rules
       are made of a regex match pattern, a substitution pattern and a set
       of actions, described by a set of optional flags.  In case of match,
       string rewriting is performed according to the substitution pattern
       that allows one to refer to substrings matched in the incoming
       string.  The actions, if any, are finally performed.  Each rule is
       executed recursively, unless altered by specific action flags; see
       "Action Flags" for details.  A default limit on the recursion level
       is set, and can be altered by the rwm-rewriteMaxPasses directive, as
       detailed in the "Additional Configuration Syntax" section.  The
       substitution pattern allows map resolution of substrings.  A map is a
       generic object that maps a substitution pattern to a value.  The
       flags are divided in "Pattern Matching Flags" and "Action Flags"; the
       former alter the regex match pattern behavior, while the latter alter
       the actions that are taken after substitution.

Pattern Matching Flags         top

       `C'    honors case in matching (default is case insensitive)

       `R'    use POSIX ''basic'' regular expressions (default is

       `M{n}' allow no more than n recursive passes for a specific rule;
              does not alter the max total count of passes, so it can only
              enforce a stricter limit for a specific rule.

Action Flags         top

       `:'    apply the rule once only (default is recursive)

       `@'    stop applying rules in case of match; the current rule is
              still applied recursively; combine with `:' to apply the
              current rule only once and then stop.

       `#'    stop current operation if the rule matches, and issue an
              `unwilling to perform' error.

       `G{n}' jump n rules back and forth (watch for loops!).  Note that
              `G{1}' is implicit in every rule.

       `I'    ignores errors in rule; this means, in case of error, e.g.
              issued by a map, the error is treated as a missed match.  The
              `unwilling to perform' is not overridden.

       `U{n}' uses n as return code if the rule matches; the flag does not
              alter the recursive behavior of the rule, so, to have it
              performed only once, it must be used in combination with `:',
              e.g.  `:U{32}' returns the value `32' (indicating
              noSuchObject) after exactly one execution of the rule, if the
              pattern matches.  As a consequence, its behavior is equivalent
              to `@', with the return code set to n; or, in other words, `@'
              is equivalent to `U{0}'.  Positive errors are allowed,
              indicating the related LDAP error codes as specified in draft-

       The ordering of the flags can be significant.  For instance: `IG{2}'
       means ignore errors and jump two lines ahead both in case of match
       and in case of error, while `G{2}I' means ignore errors, but jump two
       lines ahead only in case of match.

       More flags (mainly Action Flags) will be added as needed.

Pattern Matching         top

       See regex(7) and/or re_format(7).

Substitution Pattern Syntax         top

       Everything starting with `$' requires substitution;

       the only obvious exception is `$$', which is turned into a single

       the basic substitution is `$<d>', where `<d>' is a digit; 0 means the
       whole string, while 1-9 is a submatch, as discussed in regex(7)
       and/or re_format(7).

       a `$' followed by a `{' invokes an advanced substitution.  The
       pattern is:

              `$' `{' [ <operator> ] <name> `(' <substitution> `)' `}'

       where <name> must be a legal name for the map, i.e.

              <name> ::= [a-z][a-z0-9]* (case insensitive)
              <operator> ::= `>' `|' `&' `&&' `*' `**' `$'

       and <substitution> must be a legal substitution pattern, with no
       limits on the nesting level.

       The operators are:

       >      sub-context invocation; <name> must be a legal, already
              defined rewrite context name

       |      external command invocation; <name> must refer to a legal,
              already defined command name (NOT IMPLEMENTED YET)

       &      variable assignment; <name> defines a variable in the running
              operation structure which can be dereferenced later; operator
              & assigns a variable in the rewrite context scope; operator &&
              assigns a variable that scopes the entire session, e.g. its
              value can be dereferenced later by other rewrite contexts

       *      variable dereferencing; <name> must refer to a variable that
              is defined and assigned for the running operation; operator *
              dereferences a variable scoping the rewrite context; operator
              ** dereferences a variable scoping the whole session, e.g. the
              value is passed across rewrite contexts

       $      parameter dereferencing; <name> must refer to an existing
              parameter; the idea is to make some run-time parameters set by
              the system available to the rewrite engine, as the client host
              name, the bind DN if any, constant parameters initialized at
              config time, and so on; no parameter is currently set by
              either back-ldap or back-meta, but constant parameters can be
              defined in the configuration file by using the rewriteParam

       Substitution escaping has been delegated to the `$' symbol, which is
       used instead of `\' in string substitution patterns because `\' is
       already escaped by slapd's low level parsing routines; as a
       consequence, regex escaping requires two `\' symbols, e.g.
       `.*\.foo\.bar' must be written as `.*\\.foo\\.bar'.

Rewrite Context         top

       A rewrite context is a set of rules which are applied in sequence.
       The basic idea is to have an application initialize a rewrite engine
       (think of Apache's mod_rewrite ...) with a set of rewrite contexts;
       when string rewriting is required, one invokes the appropriate
       rewrite context with the input string and obtains the newly rewritten
       one if no errors occur.

       Each basic server operation is associated to a rewrite context; they
       are divided in two main groups: client -> server and server -> client

       client -> server:

              (default)            if defined and no specific context
                                   is available
              bindDN               bind
              searchDN             search
              searchFilter         search
              searchFilterAttrDN   search
              compareDN            compare
              compareAttrDN        compare AVA
              addDN                add
              addAttrDN            add AVA (DN portion of "ref" excluded)
              modifyDN             modify
              modifyAttrDN         modify AVA (DN portion of "ref" excluded)
              referralAttrDN       add/modify DN portion of referrals
                                   (default to none)
              renameDN             modrdn (the old DN)
              newSuperiorDN        modrdn (the new parent DN, if any)
              newRDN               modrdn (the new relative DN)
              deleteDN             delete
              exopPasswdDN         password modify extended operation DN

       server -> client:

              searchEntryDN        search (only if defined; no default;
                                   acts on DN of search entries)
              searchAttrDN         search AVA (only if defined; defaults
                                   to searchEntryDN; acts on DN-syntax
                                   attributes of search results)
              matchedDN            all ops (only if applicable; defaults
                                   to searchEntryDN)
              referralDN           all ops (only if applicable; defaults
                                   to none)

Basic Configuration Syntax         top

       All rewrite/remap directives start with the prefix rwm-; for
       backwards compatibility with the historical slapd-ldap(5) and
       slapd-meta(5) builtin rewrite/remap capabilities, the prefix may be
       omitted, but this practice is strongly discouraged.

       rwm-rewriteEngine { on | off }
              If `on', the requested rewriting is performed; if `off', no
              rewriting takes place (an easy way to stop rewriting without
              altering too much the configuration file).

       rwm-rewriteContext <context name> [ alias <aliased context name> ]
              <Context name> is the name that identifies the context, i.e.
              the name used by the application to refer to the set of rules
              it contains.  It is used also to reference sub contexts in
              string rewriting.  A context may alias another one.  In this
              case the alias context contains no rule, and any reference to
              it will result in accessing the aliased one.

       rwm-rewriteRule <regex match pattern> <substitution pattern> [
       <flags> ]
              Determines how a string can be rewritten if a pattern is
              matched.  Examples are reported below.

Additional Configuration Syntax         top

       rwm-rewriteMap <map type> <map name> [ <map attrs> ]
              Allows one to define a map that transforms substring rewriting
              into something else.  The map is referenced inside the
              substitution pattern of a rule.

       rwm-rewriteParam <param name> <param value>
              Sets a value with global scope, that can be dereferenced by
              the command `${$paramName}'.

       rwm-rewriteMaxPasses <number of passes> [<number of passes per rule>]
              Sets the maximum number of total rewriting passes that can be
              performed in a single rewrite operation (to avoid loops).  A
              safe default is set to 100; note that reaching this limit is
              still treated as a success; recursive invocation of rules is
              simply interrupted.  The count applies to the rewriting
              operation as a whole, not to any single rule; an optional per-
              rule limit can be set.  This limit is overridden by setting
              specific per-rule limits with the `M{n}' flag.

MAPS         top

       Currently, few maps are builtin but additional map types may be
       registered at runtime.

       Supported maps are:

       LDAP <URI> [bindwhen=<when>] [version=<version>] [binddn=<DN>]
              The LDAP map expands a value by performing a simple LDAP
              search.  Its configuration is based on a mandatory URI, whose
              attrs portion must contain exactly one attribute (use entryDN
              to fetch the DN of an entry).  If a multi-valued attribute is
              used, only the first value is considered.

              The parameter bindwhen determines when the connection is
              established.  It can take the values now, later, and
              everytime, respectively indicating that the connection should
              be created at startup, when required, or any time it is used.
              In the former two cases, the connection is cached, while in
              the latter a fresh new one is used all times.  This is the

              The parameters binddn and credentials represent the DN and the
              password that is used to perform an authenticated simple bind
              before performing the search operation; if not given, an
              anonymous connection is used.

              The parameter version can be 2 or 3 to indicate the protocol
              version that must be used.  The default is 3.

       slapd <URI>
              The slapd map expands a value by performing an internal LDAP
              search.  Its configuration is based on a mandatory URI, which
              must begin with ldap:/// (i.e., it must be an LDAP URI and it
              must not specify a host).  As with the LDAP map, the attrs
              portion must contain exactly one attribute, and if a multi-
              valued attribute is used, only the first value is considered.


       # set to `off' to disable rewriting
       rwm-rewriteEngine on

       # the rules the "suffixmassage" directive implies
       rwm-rewriteEngine on
       # all dataflow from client to server referring to DNs
       rwm-rewriteContext default
       rwm-rewriteRule "(.+,)?<virtualnamingcontext>$" "$1<realnamingcontext>" ":"
       # empty filter rule
       rwm-rewriteContext searchFilter
       # all dataflow from server to client
       rwm-rewriteContext searchEntryDN
       rwm-rewriteRule "(.+,)?<realnamingcontext>$" "$1<virtualnamingcontext>" ":"
       rwm-rewriteContext searchAttrDN alias searchEntryDN
       rwm-rewriteContext matchedDN alias searchEntryDN
       # misc empty rules
       rwm-rewriteContext referralAttrDN
       rwm-rewriteContext referralDN

       # Everything defined here goes into the `default' context.
       # This rule changes the naming context of anything sent
       # to `dc=home,dc=net' to `dc=OpenLDAP, dc=org'

       rwm-rewriteRule "(.+,)?dc=home,[ ]?dc=net$"
                   "$1dc=OpenLDAP, dc=org"  ":"

       # since a pretty/normalized DN does not include spaces
       # after rdn separators, e.g. `,', this rule suffices:

       rwm-rewriteRule "(.+,)?dc=home,dc=net$"
                   "$1dc=OpenLDAP,dc=org"  ":"

       # Start a new context (ends input of the previous one).
       # This rule adds blanks between DN parts if not present.
       rwm-rewriteContext  addBlanks
       rwm-rewriteRule     "(.*),([^ ].*)" "$1, $2"

       # This one eats blanks
       rwm-rewriteContext  eatBlanks
       rwm-rewriteRule     "(.*), (.*)" "$1,$2"

       # Here control goes back to the default rewrite
       # context; rules are appended to the existing ones.
       # anything that gets here is piped into rule `addBlanks'
       rwm-rewriteContext  default
       rwm-rewriteRule     ".*" "${>addBlanks($0)}" ":"

       # Rewrite the search base according to `default' rules.
       rwm-rewriteContext  searchDN alias default

       # Search results with OpenLDAP DN are rewritten back with
       # `dc=home,dc=net' naming context, with spaces eaten.
       rwm-rewriteContext  searchEntryDN
       rwm-rewriteRule     "(.*[^ ],)?[ ]?dc=OpenLDAP,[ ]?dc=org$"
                       "${>eatBlanks($1)}dc=home,dc=net"    ":"

       # Bind with email instead of full DN: we first need
       # an ldap map that turns attributes into a DN (the
       # argument used when invoking the map is appended to
       # the URI and acts as the filter portion)
       rwm-rewriteMap ldap attr2dn "ldap://host/dc=my,dc=org?dn?sub"

       # Then we need to detect DN made up of a single email,
       # e.g. `'; note that the rule
       # in case of match stops rewriting; in case of error,
       # it is ignored.  In case we are mapping virtual
       # to real naming contexts, we also need to rewrite
       # regular DNs, because the definition of a bindDN
       # rewrite context overrides the default definition.
       rwm-rewriteContext bindDN
       rwm-rewriteRule "^mail=[^,]+@[^,]+$" "${attr2dn($0)}" ":@I"

       # This is a rather sophisticated example. It massages a
       # search filter in case who performs the search has
       # administrative privileges.  First we need to keep
       # track of the bind DN of the incoming request, which is
       # stored in a variable called `binddn' with session scope,
       # and left in place to allow regular binding:
       rwm-rewriteContext  bindDN
       rwm-rewriteRule     ".+" "${&&binddn($0)}$0" ":"

       # A search filter containing `uid=' is rewritten only
       # if an appropriate DN is bound.
       # To do this, in the first rule the bound DN is
       # dereferenced, while the filter is decomposed in a
       # prefix, in the value of the `uid=<arg>' AVA, and
       # in a suffix. A tag `<>' is appended to the DN.
       # If the DN refers to an entry in the `ou=admin' subtree,
       # the filter is rewritten OR-ing the `uid=<arg>' with
       # `cn=<arg>'; otherwise it is left as is. This could be
       # useful, for instance, to allow apache's auth_ldap-1.4
       # module to authenticate users with both `uid' and
       # `cn', but only if the request comes from a possible
       # `cn=Web auth,ou=admin,dc=home,dc=net' user.
       rwm-rewriteContext searchFilter
       rwm-rewriteRule "(.*\\()uid=([a-z0-9_]+)(\\).*)"
       rwm-rewriteRule "^[^,]+,ou=admin,dc=home,dc=net$"
         "${*prefix}|(uid=${*arg})(cn=${*arg})${*suffix}" ":@I"
       rwm-rewriteRule ".*<>$" "${*prefix}uid=${*arg}${*suffix}" ":"

       # This example shows how to strip unwanted DN-valued
       # attribute values from a search result; the first rule
       # matches DN values below "ou=People,dc=example,dc=com";
       # in case of match the rewriting exits successfully.
       # The second rule matches everything else and causes
       # the value to be rejected.
       rwm-rewriteContext searchEntryDN
       rwm-rewriteRule ".+,ou=People,dc=example,dc=com$" "$0" ":@"
       rwm-rewriteRule ".*" "" "#"


       The following directives map the object class `groupOfNames' to the
       object class `groupOfUniqueNames' and the attribute type `member' to
       the attribute type `uniqueMember':

              map objectclass groupOfNames groupOfUniqueNames
              map attribute uniqueMember member

       This presents a limited attribute set from the foreign server:

              map attribute cn *
              map attribute sn *
              map attribute manager *
              map attribute description *
              map attribute *

       These lines map cn, sn, manager, and description to themselves, and
       any other attribute gets "removed" from the object before it is sent
       to the client (or sent up to the LDAP server).  This is obviously a
       simplistic example, but you get the point.

FILES         top

              default slapd configuration file

SEE ALSO         top

       slapd.conf(5), slapd-config(5), slapd-ldap(5), slapd-meta(5),
       slapd-relay(5), slapd(8), regex(7), re_format(7).

AUTHOR         top

       Pierangelo Masarati; based on back-ldap rewrite/remap features by
       Howard Chu, Pierangelo Masarati.

COLOPHON         top

       This page is part of the OpenLDAP (an open source implementation of
       the Lightweight Directory Access Protocol) project.  Information
       about the project can be found at ⟨⟩.  If you
       have a bug report for this manual page, see
       ⟨⟩.  This page was obtained from the
       project's upstream Git repository
       ⟨⟩ on 2020-11-01.  (At
       that time, the date of the most recent commit that was found in the
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Pages that refer to this page: slapd.backends(5)slapd.conf(5)slapd-config(5)slapd-ldap(5)slapd.overlays(5)slapd-relay(5)