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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 RFC4511.
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-
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.
escape [escape2dn|escape2filter|unescapedn|unescapefilter]...
The escape map makes it possible use DNs or their parts in
filter strings and vice versa. It processes a value
according to the operations listed in order. Supported
operations include:
escape2dn
takes a string and escapes it so it can safely be
pasted in a DN
escape2filter
takes a string and escapes it so it can safely be
pasted in a filter
unescapedn
takes a string and undoes DN escaping
unescapefilter
takes a string and undoes filter escaping
It is advised that each escape map ends with an escape
operation as that is the only safe way to handle arbitrary
strings.
# 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($1)}dc=home,dc=net" ":"
# Transform a DN value such that it can be used in a filter
rwm-rewriteMap escape dn2filter unescapedn escape2filter
# Bind with email instead of full DN: we first need
# an ldap map that turns attributes into a DN (the
# argument used when invoking the map is appended to
# the URI and acts as the filter portion)
rwm-rewriteMap ldap attr2dn "ldap://host/dc=my,dc=org?dn?sub"
# Then we need to detect DN made up of a single email,
# e.g. `mail=someone@example.com'; note that the rule
# in case of match stops rewriting; in case of error,
# it is ignored. In case we are mapping virtual
# to real naming contexts, we also need to rewrite
# regular DNs, because the definition of a bindDN
# rewrite context overrides the default definition.
#
# While actual email addresses tend not to contain filter
# special characters, the provided Bind DN has no such
# restrictions.
rwm-rewriteContext bindDN
rwm-rewriteRule "^(mail=)([^,]+@[^,]+)$"
"${attr2dn($1${dn2filter($2)})}" ":@I"
# This is a rather sophisticated example. It massages a
# search filter in case who performs the search has
# administrative privileges. First we need to keep
# track of the bind DN of the incoming request, which is
# stored in a variable called `binddn' with session scope,
# and left in place to allow regular binding:
rwm-rewriteContext bindDN
rwm-rewriteRule ".+" "${&&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
⟨https://git.openldap.org/openldap/openldap.git⟩ on 2024-06-14.
(At that time, the date of the most recent commit that was found
in the repository was 2024-06-13.) If you discover any rendering
problems in this HTML version of the page, or you believe there
is a better or more up-to-date source for the page, or 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)
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HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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