# slapo-rwm

## NAME



           slapo-rwm - rewrite/remap overlay to slapd
    


## SYNOPSIS



           ETCDIR/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
           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.
    


## 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
           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".
    


## 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 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



           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



           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



           **`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 _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.
    


## 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 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** '.
    


## 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-**
    
           **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 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



           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.
    


## 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"    ":"
    
           # 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 ".*" "" "#"
    


## 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



           ETCDIR/slapd.conf
                  default slapd configuration file
    


* * *