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SLAPO-RWM(5)                                                                                    SLAPO-RWM(5)



NAME
       slapo-rwm - rewrite/remap overlay to slapd

SYNOPSIS
       /etc/openldap/slapd.conf

DESCRIPTION
       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  conjunc-tion conjunction
       tion  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.

MAPPING
       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  object-Classes objectClasses
       Classes 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  subschemaSuben-try subschemaSubentry
       try  of  the remote server; the problem should not exist when remapping a local database.  Note, how-ever, however,
       ever, 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  nor-malization normalization
       malization 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".

SUFFIX MASSAGING
       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 to
       create virtual views of databases.  A distinguishing feature of this overlay is that, when  instanti-ated instantiated
       ated  before any database, it can modify the DN of requests before database selection.  For this rea-son, reason,
       son, 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,  searchAt-trDN searchAttrDN
              trDN  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
       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 behav-ior behavior
       ior 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 dedi-cated dedicated
       cated to the LDAP backend):


Passes
       An  incoming  string  is matched against a set of rewriteRules.  Rules are made of a regex match pat-tern, pattern,
       tern, 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 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  direc-tive, directive,
       tive,  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
       `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.

Action Flags
       `:'    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.

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

Substitution Pattern Syntax
       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 param-eter parameter
              eter 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 con-sequence, consequence,
       sequence,  regex  escaping  requires  two  `\'  symbols,  e.g.  `.*\.foo\.bar'  must  be  written  as
       `.*\\.foo\\.bar'.

Rewrite Context
       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)


Basic Configuration Syntax
       All rewrite/remap directives start with the prefix rwm-; for backwards compatibility with the histor-ical historical
       ical  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
       rwm-rewriteMap <map type> <map name> [ <map attrs> ]
              Allows  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
       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 con-sidered. considered.
              sidered.

              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 per-form perform
              form 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.


REWRITE CONFIGURATION EXAMPLES
       # 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 ".*" "" "#"

MAPPING EXAMPLES
       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
       /etc/openldap/slapd.conf
              default slapd configuration file

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

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



OpenLDAP 2.4.28                                  2011/11/24                                     SLAPO-RWM(5)