SLAPO-RWM(5) File Formats Manual SLAPO-RWM(5)
slapo-rwm - rewrite/remap overlay to slapd
ETCDIR/slapd.conf
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
slapd-relay(5).
This overlay is experimental.
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.
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):
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.
`C' honors case in matching (default is case insensitive)
`R' use POSIX ''basic'' regular expressions (default is
''extended'')
`M{n}' allow no more than n recursive passes for a specific rule;
does not alter the max total count of passes, so it can only
enforce a stricter limit for a specific rule.
`:' 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-
ietf-ldapbis-protocol.
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.
See regex(7) and/or re_format(7).
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
directive.
Substitution escaping has been delegated to the `$' symbol, which is
used instead of `\' in string substitution patterns because `\' is
already escaped by slapd's low level parsing routines; as a
consequence, regex escaping requires two `\' symbols, e.g.
`.*\.foo\.bar' must be written as `.*\\.foo\\.bar'.
A rewrite context is a set of rules which are applied in sequence.
The basic idea is to have an application initialize a rewrite engine
(think of Apache's mod_rewrite ...) with a set of rewrite contexts;
when string rewriting is required, one invokes the appropriate
rewrite context with the input string and obtains the newly rewritten
one if no errors occur.
Each basic server operation is associated to a rewrite context; they
are divided in two main groups: client -> server and server -> client
rewriting.
client -> server:
(default) if defined and no specific context
is available
bindDN bind
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)
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.
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.
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>]
[credentials=<cred>]
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
default.
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($1)}dc=home,dc=net" ":"
# Bind with email instead of full DN: we first need
# an ldap map that turns attributes into a DN (the
# argument used when invoking the map is appended to
# the URI and acts as the filter portion)
rwm-rewriteMap ldap attr2dn "ldap://host/dc=my,dc=org?dn?sub"
# Then we need to detect DN made up of a single email,
# e.g. `mail=someone@example.com'; note that the rule
# in case of match stops rewriting; in case of error,
# it is ignored. In case we are mapping virtual
# to real naming contexts, we also need to rewrite
# regular DNs, because the definition of a bindDN
# rewrite context overrides the default definition.
rwm-rewriteContext bindDN
rwm-rewriteRule "^mail=[^,]+@[^,]+$" "${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)}$0" ":"
# A search filter containing `uid=' is rewritten only
# if an appropriate DN is bound.
# To do this, in the first rule the bound DN is
# dereferenced, while the filter is decomposed in a
# prefix, in the value of the `uid=<arg>' AVA, and
# in a suffix. A tag `<>' is appended to the DN.
# If the DN refers to an entry in the `ou=admin' subtree,
# the filter is rewritten OR-ing the `uid=<arg>' with
# `cn=<arg>'; otherwise it is left as is. This could be
# useful, for instance, to allow apache's auth_ldap-1.4
# module to authenticate users with both `uid' and
# `cn', but only if the request comes from a possible
# `cn=Web auth,ou=admin,dc=home,dc=net' user.
rwm-rewriteContext searchFilter
rwm-rewriteRule "(.*\\()uid=([a-z0-9_]+)(\\).*)"
"${**binddn}<>${&prefix($1)}${&arg($2)}${&suffix($3)}"
":I"
rwm-rewriteRule "^[^,]+,ou=admin,dc=home,dc=net$"
"${*prefix}|(uid=${*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.
ETCDIR/slapd.conf
default slapd configuration file
slapd.conf(5), slapd-config(5), slapd-ldap(5), slapd-meta(5),
slapd-relay(5), slapd(8), regex(7), re_format(7).
Pierangelo Masarati; based on back-ldap rewrite/remap features by
Howard Chu, Pierangelo Masarati.
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 ⟨http://www.openldap.org/⟩. If you
have a bug report for this manual page, see
⟨http://www.openldap.org/its/⟩. This page was obtained from the
project's upstream Git repository
⟨git://git.openldap.org/openldap.git⟩ on 2017-07-05. If you discover
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you have corrections or improvements to the information in this
COLOPHON (which is not part of the original manual page), send a mail
to man-pages@man7.org
OpenLDAP LDVERSION RELEASEDATE SLAPO-RWM(5)
Pages that refer to this page: slapd.backends(5), slapd.conf(5), slapd-config(5), slapd-ldap(5), slapd.overlays(5), slapd-relay(5)