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           The  meta backend to slapd(8) performs basic LDAP proxying with respect
           to a set of remote LDAP servers,  called  "targets".   The  information
           contained  in  these  servers can be presented as belonging to a single
           Directory Information Tree (DIT).
           A basic knowledge of the functionality of the slapd-ldap(5) backend  is
           recommended.   This  backend has been designed as an enhancement of the
           ldap backend.  The two backends share many features (actually they also
           share  portions  of code).  While the ldap backend is intended to proxy
           operations directed to a single server,  the  meta  backend  is  mainly
           intended  for  proxying of multiple servers and possibly naming context
           masquerading.  These features, although useful in many  scenarios,  may
           result  in  excessive overhead for some applications, so its use should
           be carefully considered.  In the examples section, some typical scenar-
           ios will be discussed.
           The  proxy instance of slapd(8) must contain schema information for the
           attributes and objectClasses used in filters, request DN  and  request-
           related data in general.  It should also contain schema information for
           the data returned by the proxied server.  It is the  responsibility  of
           the  proxy  administrator to keep the schema of the proxy lined up with
           that of the proxied server.
           Note: When looping back to the same instance of slapd(8), each  connec-
           tion requires a new thread; as a consequence, slapd(8) must be compiled
           with thread support, and the threads parameter may need some tuning; in
           those  cases,  unless  the multiple target feature is required, one may
           consider using slapd-relay(5) instead, which performs the relayed oper-
           ation internally and thus reuses the same connection.


           There  are  examples  in various places in this document, as well as in
           the slapd/back-meta/data/ directory in the OpenLDAP source tree.


           These slapd.conf options apply to the META backend database.  That  is,
           they  must follow a "database meta" line and come before any subsequent
           "backend" or "database" lines.  Other database options are described in
           the slapd.conf(5) manual page.
           Note:  In  early versions of back-ldap and back-meta it was recommended
           to always set
                  lastmod  off
           for ldap and meta databases.  This  was  required  because  operational
                  This  directive  causes  a  cached  connection  to be dropped an
                  recreated after a given ttl, regardless of being idle or not.
           default-target none
                  This directive forces the backend to reject all those operations
                  that  must  resolve  to a single target in case none or multiple
                  targets are selected.  They include: add, delete,  modify,  mod-
                  rdn;  compare  is  not  included, as well as bind since, as they
                  don't alter entries, in case of multiple matches an  attempt  is
                  made  to perform the operation on any candidate target, with the
                  constraint that at most one must succeed.   This  directive  can
                  also  be  used when processing targets to mark a specific target
                  as default.
           dncache-ttl {DISABLED|forever|<ttl>}
                  This directive sets the time-to-live  of  the  DN  cache.   This
                  caches  the  target  that  holds  a  given DN to speed up target
                  selection in case multiple targets would result from an uncached
                  search;  forever means cache never expires; disabled means no DN
                  caching; otherwise a valid ( > 0 ) ttl is required, in the  for-
                  mat illustrated for the idle-timeout directive.
           onerr {CONTINUE|report|stop}
                  This directive allows to select the behavior in case an error is
                  returned by one target during a search.  The default,  continue,
                  consists  in  continuing the operation, trying to return as much
                  data as possible.  If the value is set to stop,  the  search  is
                  terminated  as  soon  as an error is returned by one target, and
                  the error is immediately propagated to the client.  If the value
                  is  set  to report, the search is continuated to the end but, in
                  case at least one target returned an error code, the first  non-
                  success error code is returned.
           norefs <NO|yes>
                  If  yes,  do not return search reference responses.  By default,
                  they are returned unless request is LDAPv2.  If set  before  any
                  target  specification, it affects all targets, unless overridden
                  by any per-target directive.
           noundeffilter <NO|yes>
                  If yes, return success instead of searching if a filter is unde-
                  fined or contains undefined portions.  By default, the search is
                  propagated after replacing undefined  portions  with  (!(object-
                  Class=*)),  which  corresponds  to the empty result set.  If set
                  before any target specification, it affects all targets,  unless
                  overridden by any per-target directive.
                  the  remote  servers with the pseudo-root identity (the identity
                  defined in each idassert-bind directive) to  be  deferred  until
                  actually  needed by subsequent operations.  Otherwise, all binds
                  as the rootdn are propagated to the targets.
           quarantine <interval>,<num>[;<interval>,<num>[...]]
                  Turns on quarantine of URIs that returned  LDAP_UNAVAILABLE,  so
                  that  an  attempt  to  reconnect  only occurs at given intervals
                  instead of any time a client requests an operation.  The pattern
                  is:  retry  only  after  at least interval seconds elapsed since
                  last attempt, for exactly num times; then use the next  pattern.
                  If  num  for the last pattern is "+", it retries forever; other-
                  wise, no more retries occur.  This directive must appear  before
                  any  target  specification; it affects all targets with the same
           rebind-as-user {NO|yes}
                  If this option is  given,  the  client's  bind  credentials  are
                  remembered  for  rebinds,  when  trying to re-establish a broken
                  connection, or when chasing a referral,  if  chase-referrals  is
                  set to yes.
           session-tracking-request {NO|yes}
                  Adds session tracking control for all requests.  The client's IP
                  and hostname, and the identity associated to  each  request,  if
                  known, are sent to the remote server for informational purposes.
                  This directive is incompatible with setting protocol-version  to
                  2.   If set before any target specification, it affects all tar-
                  gets, unless overridden by any per-target directive.
           single-conn {NO|yes}
                  Discards current cached connection when the client rebinds.
           use-temporary-conn {NO|yes}
                  when set to yes, create a temporary connection whenever  compet-
                  ing  with  other threads for a shared one; otherwise, wait until
                  the shared connection is available.


           Target specification starts with a "uri" directive:
           uri <protocol>://[<host>]/<naming context> [...]
                  The <protocol> part can be anything  ldap_initialize(3)  accepts
                  ({ldap|ldaps|ldapi}  and  variants);  the <host> may be omitted,
                  defaulting to whatever is set in ldap.conf(5).  The <naming con-
                  same server, the directive
                  suffix "dc=foo,dc=com"
                  uri    "ldap://,dc=com" "ldap://"
                  causes to be contacted whenever  does  not
                  respond.   In  that case, the URI list is internally rearranged,
                  by moving unavailable URIs to the end, so that  further  connec-
                  tion attempts occur with respect to the last URI that succeeded.
           acl-authcDN <administrative DN for access control purposes>
                  DN which is used to query the target server for acl checking, as
                  in  the  LDAP backend; it is supposed to have read access on the
                  target server to attributes used on the proxy for acl  checking.
                  There  is no risk of giving away such values; they are only used
                  to check permissions.  The acl-authcDN identity is by  no  means
                  implicitly  used  by  the  proxy when the client connects anony-
           acl-passwd <password>
                  Password used with the acl-authcDN above.
           bind-timeout <microseconds>
                  This directive defines the timeout, in microseconds,  used  when
                  polling for response after an asynchronous bind connection.  The
                  initial call to ldap_result(3) is  performed  with  a  trade-off
                  timeout  of  100000  us;  if that results in a timeout exceeded,
                  subsequent calls use the value provided with bind-timeout.   The
                  default  value is used also for subsequent calls if bind-timeout
                  is not specified.  If set before any  target  specification,  it
                  affects  all targets, unless overridden by any per-target direc-
           chase-referrals {YES|no}
                  enable/disable automatic referral chasing, which is delegated to
                  the  underlying  libldap, with rebinding eventually performed if
                  the rebind-as-user directive is used.  The default is  to  chase
                  referrals.   If  set before any target specification, it affects
                  all targets, unless overridden by any per-target directive.
           client-pr {accept-unsolicited|DISABLE|<size>}
                  This feature allows to use RFC 2696 Paged Results  control  when
                  performing  search  operations with a specific target, irrespec-
                  tive of the client's request.  When  set  to  a  numeric  value,
                  Paged Results control is always used with size as the page size.
                  When set to accept-unsolicited, unsolicited Paged  Results  con-
                  trol  responses  are accepted and honored for compatibility with
           filter <pattern>
                  This  directive allows specifying a regex(5) pattern to indicate
                  what search filter terms are actually served by a target.
                  In a search request, if the search filter  matches  the  pattern
                  the target is considered while fulfilling the request; otherwise
                  the target is ignored. There may be multiple occurrences of  the
                  filter directive for each target.
           idassert-authzFrom <authz-regexp>
                  if  defined,  selects  what  local  identities are authorized to
                  exploit the identity assertion feature.  The string  <authz-reg-
                  exp> follows the rules defined for the authzFrom attribute.  See
                  slapd.conf(5), section related to authz-policy, for  details  on
                  the syntax of this field.
           idassert-bind    bindmethod=none|simple|sasl    [binddn=<simple    DN>]
                  [credentials=<simple    password>]    [saslmech=<SASL     mech>]
                  [secprops=<properties>] [realm=<realm>] [authcId=<authentication
                  ID>]  [authzId=<authorization  ID>]  [authz={native|proxyauthz}]
                  [mode=<mode>]     [flags=<flags>]     [starttls=no|yes|critical]
                  [tls_cert=<file>]      [tls_key=<file>]      [tls_cacert=<file>]
                  [tls_cacertdir=<path>]      [tls_reqcert=never|allow|try|demand]
                  [tls_ciphersuite=<ciphers>] [tls_protocol_min=<major>[.<minor>]]
                  Allows  to  define  the  parameters of the authentication method
                  that is internally used by the proxy  to  authorize  connections
                  that are authenticated by other databases.  The identity defined
                  by this directive, according to the properties associated to the
                  authentication  method,  is  supposed to have auth access on the
                  target server to attributes used on the proxy for authentication
                  and  authorization,  and  to  be allowed to authorize the users.
                  This requires to have proxyAuthz privileges on  a  wide  set  of
                  DNs,  e.g.  authzTo=dn.subtree:"", and the remote server to have
                  authz-policy set to to or both.  See slapd.conf(5)  for  details
                  on  these  statements  and for remarks and drawbacks about their
                  usage.  The supported bindmethods are
                  where none  is  the  default,  i.e.  no  identity  assertion  is
                  The authz parameter is used to instruct the SASL bind to exploit
                  native SASL authorization, if available; since  connections  are
                  cached,  this  should only be used when authorizing with a fixed
                  identity (e.g. by means of the authzDN or  authzID  parameters).
                  Otherwise,  the  default proxyauthz is used, i.e. the proxyAuthz
                  control (Proxied  Authorization,  RFC  4370)  is  added  to  all
                  according to the authz rules; see slapd.conf(5) for details.  In
                  the latter case, whether or not the dn: prefix is  present,  the
                  string must pass DN validation and normalization.
                  The  default  mode  is legacy, which implies that the proxy will
                  either perform a simple bind as the authcDN or a  SASL  bind  as
                  the  authcID  and  assert  the  client's identity when it is not
                  anonymous.  Direct binds are always proxied.   The  other  modes
                  imply that the proxy will always either perform a simple bind as
                  the authcDN or a SASL bind as the authcID, unless restricted  by
                  idassert-authzFrom   rules   (see  below),  in  which  case  the
                  operation will fail;  eventually,  it  will  assert  some  other
                  identity  according  to  <mode>.  Other identity assertion modes
                  are anonymous and self, which respectively mean that  the  empty
                  or  the  client's  identity  will be asserted; none, which means
                  that no proxyAuthz control will be used, so the authcDN  or  the
                  authcID  identity  will be asserted.  For all modes that require
                  the use of the proxyAuthz control,  on  the  remote  server  the
                  proxy identity must have appropriate authzTo permissions, or the
                  asserted identities must have appropriate authzFrom permissions.
                  Note,  however,  that  the ID assertion feature is mostly useful
                  when the asserted identities do not exist on the remote  server.
                  Flags can be
                  When  the  override flag is used, identity assertion takes place
                  even when the database is authorizing for the  identity  of  the
                  client,  i.e. after binding with the provided identity, and thus
                  authenticating it, the proxy  performs  the  identity  assertion
                  using the configured identity and authentication method.
                  When  the  prescriptive  flag  is used (the default), operations
                  fail with inappropriateAuthentication for those identities whose
                  assertion is not allowed by the idassert-authzFrom patterns.  If
                  the non-prescriptive flag  is  used,  operations  are  performed
                  anonymously  for those identities whose assertion is not allowed
                  by the idassert-authzFrom patterns.
                  When the proxy-authz-non-critical flag is  used  (the  default),
                  the  proxyAuthz  control is not marked as critical, in violation
                  of RFC 4370.  Use of proxy-authz-critical is recommended.
                  The TLS settings default to the  same  as  the  main  slapd  TLS
                  settings, except for tls_reqcert which defaults to "demand".
                  The  identity  associated  to  this  directive  is also used for
                  privileged operations  whenever  idassert-bind  is  defined  and
                  acl-bind is not.  See acl-bind for details.
                  The keepalive parameter sets the values  of  idle,  probes,  and
                  interval  used  to  check whether a socket is alive; idle is the
                  number of seconds a connection needs to remain idle  before  TCP
                  starts sending keepalive probes; probes is the maximum number of
                  keepalive probes TCP should send before dropping the connection;
                  interval  is  interval  in  seconds between individual keepalive
                  probes.  Only some systems support the  customization  of  these
                  values;  the  keepalive  parameter  is  ignored  otherwise,  and
                  system-wide settings are used.
           map {attribute|objectclass} [<local name>|*] {<foreign name>|*}
                  This maps object classes and attributes as in the LDAP  backend.
                  See slapd-ldap(5).
           network-timeout <time>
                  Sets  the  network  timeout  value after which poll(2)/select(2)
                  following a connect(2) returns in  case  of  no  activity.   The
                  value   is   in   seconds,  and  it  can  be  specified  as  for
                  idle-timeout.   If  set  before  any  target  specification,  it
                  affects   all  targets,  unless  overridden  by  any  per-target
           nretries {forever|never|<nretries>}
                  This directive defines how many times a bind should  be  retried
                  in case of temporary failure in contacting a target.  If defined
                  before any target specification, it applies to all  targets  (by
                  default,  3  times);  the  global  value  can  be  overridden by
                  redefinitions inside each target specification.
           rewrite* ...
                  The rewrite options are described in the "REWRITING" section.
           subtree-{exclude|include} <rule>
                  This directive allows to indicate  what  subtrees  are  actually
                  served by a target.  The syntax of the supported rules is
                  <rule>: [dn[.<style>]:]<pattern>
                  <style>: subtree|children|regex
                  When <style> is either subtree or children the <pattern> is a DN
                  that must be within the naming context  served  by  the  target.
                  When  <style>  is regex the <pattern> is a regex(5) pattern.  If
                  the dn.<style>: prefix is  omitted,  dn.subtree:  is  implicitly
                  assumed for backward compatibility.
                  In  the  subtree-exclude form if the request DN matches at least
                      |    T    |    F    | candidate         |
                      |    F    |    F    | not candidate     |
                  There  may  be  multiple  occurrences  of the subtree-exclude or
                  subtree-include directive for each of the targets, but they  are
                  mutually exclusive.
           suffixmassage <virtual naming context> <real naming context>
                  All  the directives starting with "rewrite" refer to the rewrite
                  engine that  has  been  added  to  slapd.   The  "suffixmassage"
                  directive  was  introduced  in  the LDAP backend to allow suffix
                  massaging  while  proxying.   It  has  been  obsoleted  by   the
                  rewriting  tools.   However, both for backward compatibility and
                  for  ease  of  configuration  when  simple  suffix  massage   is
                  required,  it  has been preserved.  It wraps the basic rewriting
                  instructions that perform suffix massaging.  See the "REWRITING"
                  section for a detailed list of the rewrite rules it implies.
           t-f-support {NO|yes|discover}
                  enable  if  the remote server supports absolute filters (see RFC
                  4526 for details).  If set to discover, support is  detected  by
                  reading  the remote server's root DSE.  If set before any target
                  specification, it affects all targets, unless overridden by  any
                  per-target directive.
           timeout [<op>=]<val> [...]
                  This directive allows to set per-operation timeouts.  Operations
                  can be
                  <op> ::= bind, add, delete, modrdn, modify, compare, search
                  The overall duration  of  the  search  operation  is  controlled
                  either  by  the  timelimit  parameter or by server-side enforced
                  time limits (see  timelimit  and  limits  in  slapd.conf(5)  for
                  details).   This  timeout parameter controls how long the target
                  can be irresponsive before the operation is aborted.  Timeout is
                  meaningless  for  the  remaining operations, unbind and abandon,
                  which do not imply any response, while it is not yet implemented
                  in  currently supported extended operations.  If no operation is
                  specified, the timeout val affects all supported operations.  If
                  specified  before  any target definition, it affects all targets
                  unless overridden by per-target directives.
                  Note: if the timeout is exceeded,  the  operation  is  cancelled
                  (according  to  the  cancel  directive);  the  protocol does not
                  provide any means to rollback operations, so the client will not
                  be  notified  about  the  result  of  the  operation,  which may


           A  powerful (and in some sense dangerous) rewrite engine has been added
           to both the LDAP and Meta backends.  While the former can gain  limited
           beneficial  effects  from  rewriting  stuff,  the  latter can become an
           amazingly powerful tool.
           Consider a couple of scenarios first.
           1) Two directory servers  share  two  levels  of  naming  context;  say
           "dc=a,dc=foo,dc=com"  and  "dc=b,dc=foo,dc=com".   Then, an unambiguous
           Meta database can be configured as:
                  database meta
                  suffix   "dc=foo,dc=com"
                  uri      "ldap://,dc=foo,dc=com"
                  uri      "ldap://,dc=foo,dc=com"
           Operations directed to a specific target can be easily resolved because
           there  are  no  ambiguities.   The  only  operation that may resolve to
           multiple targets is a search with base  "dc=foo,dc=com"  and  scope  at
           least "one", which results in spawning two searches to the targets.
           2a)  Two  directory  servers don't share any portion of naming context,
           but they'd present as a single DIT [Caveat:  uniqueness  of  (massaged)
           entries  among  the  two  servers  is assumed; integrity checks risk to
           incur in excessive overhead and have not  been  implemented].   Say  we
           have  "dc=bar,dc=org" and "o=Foo,c=US", and we'd like them to appear as
           branches   of    "dc=foo,dc=com",    say    "dc=a,dc=foo,dc=com"    and
           "dc=b,dc=foo,dc=com".  Then we need to configure our Meta backend as:
                  database      meta
                  suffix        "dc=foo,dc=com"
                  uri           "ldap://,dc=foo,dc=com"
                  suffixmassage "dc=a,dc=foo,dc=com" "dc=bar,dc=org"
                  uri           "ldap://,dc=foo,dc=com"
                  suffixmassage "dc=b,dc=foo,dc=com" "o=Foo,c=US"
           Again,  operations  can  be  resolved  without ambiguity, although some
           rewriting is required.  Notice that the virtual naming context of  each
           target  is  a  branch of the database's naming context; it is rewritten
           back and  forth  when  operations  are  performed  towards  the  target
           servers.  What "back and forth" means will be clarified later.
           When  a  search with base "dc=foo,dc=com" is attempted, if the scope is
           "base" it fails with "no such object"; in fact, the common root of  the
           two  targets  (prior  to  massaging)  does  not exist.  If the scope is
           "one", both targets are  contacted  with  the  base  replaced  by  each
           target's  base;  the  scope  is derated to "base".  In general, a scope
                  suffixmassage "dc=foo,dc=com" "dc=bar,dc=org"
                  uri           "ldap://,dc=com"
                  suffixmassage "dc=foo,dc=com" "o=Foo,c=US"
           All the previous considerations hold, except that now there is  no  way
           to  unambiguously  resolve a DN.  In this case, all the operations that
           require an unambiguous target selection will  fail  unless  the  DN  is
           already   cached   or   a  default  target  has  been  set.   Practical
           configurations may result as a combination of all the above  scenarios.


           Note on ACLs: at present you may add whatever ACL rule you desire to to
           the Meta (and LDAP) backends.  However, the meaning  of  an  ACL  on  a
           proxy  may  require  some  considerations.   Two  philosophies  may  be
           a) the remote server dictates the permissions; the proxy simply  passes
           back what it gets from the remote server.
           b) the remote server unveils "everything"; the proxy is responsible for
           protecting data from unauthorized access.
           Of course the latter  sounds  unreasonable,  but  it  is  not.   It  is
           possible  to  imagine  scenarios  in which a remote host discloses data
           that can be considered "public" inside an intranet, and  a  proxy  that
           connects it to the internet may impose additional constraints.  To this
           purpose, the proxy should be able to comply with all the  ACL  matching
           criteria  that the server supports.  This has been achieved with regard
           to all the criteria supported by slapd except  a  special  subtle  case
           (please   file   an   ITS   if   you   can   find   other   exceptions:
           <>).  The rule
                  access to dn="<dn>" attrs=<attr>
                         by dnattr=<dnattr> read
                         by * none
           cannot be matched iff the attribute that is being requested, <attr>, is
           NOT  <dnattr>,  and the attribute that determines membership, <dnattr>,
           has not been requested (e.g. in a search)
           In fact this ACL is resolved by slapd using the  portion  of  entry  it
           retrieved   from  the  remote  server  without  requiring  any  further
           intervention of the backend, so, if the <dnattr> attribute has not been
           fetched,  the  match  cannot  be  assessed because the attribute is not
           present, not because no value matches the requirement!
           Note on ACLs and attribute mapping: ACLs  are  applied  to  the  mapped
           attributes;  for  instance,  if the attribute locally known as "foo" is
           mapped to "bar" on a remote server, then local ACLs apply to  attribute
           "foo"  and  are  totally unaware of its remote name.  The remote server
           will check permissions for "bar", and the local  server  will  possibly
           An  incoming  string is matched against a set of rules.  Rules are made
           of a regex match pattern, a substitution pattern and a set of  actions,
           described  by  a  set of flags.  In case of match a 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.  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 action that is taken after substitution.

    Pattern Matching Flags

           'C'    honors case in matching (default is case insensitive)
           'R'    use   POSIX   ''basic''   regular   expressions   (default    is
           'M{n}' allow  no more than n recursive passes for a specific rule; does
                  not alter the max total count of passes, so it can only  enforce
                  a stricter limit for a specific rule.

    Action Flags

           ':'    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{16}'  returns  the  value  '16'  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}'.
                  By convention, the freely available codes are above 16 included;
                  the others are reserved.
           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.
           a  '%' followed by a '{' invokes an advanced substitution.  The pattern
                  '%' '{' [ <op> ] <name> '(' <substitution> ')' '}'
           where <name> must be a legal name for the map, i.e.
                  <name> ::= [a-z][a-z0-9]* (case insensitive)
                  <op> ::= '>' '|' '&' '&&' '*' '**' '$'
           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 IMPL.)
           &      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
                  searchFilterAttrDN   search
                  compareDN            compare
                  compareAttrDN        compare AVA
                  addDN                add
                  addAttrDN            add AVA
                  modifyDN             modify
                  modifyAttrDN         modify AVA
                  modrDN               modrdn
                  newSuperiorDN        modrdn
                  deleteDN             delete
                  exopPasswdDN         password modify extended operation DN if proxy
           server -> client:
                  searchResult         search (only if defined; no default;
                                       acts on DN and DN-syntax attributes
                                       of search results)
                  searchAttrDN         search AVA
                  matchedDN            all ops (only if applicable)

    Basic configuration syntax

           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).
           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.
           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:

           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.
           rewriteParam <param name> <param value>
                  Sets a value with global scope, that can be dereferenced by  the
                  command '%{$paramName}'.
           rewriteMaxPasses <number of passes> [<number of passes per rule>]
                  Sets  the  maximum  number of total rewriting passes that can be
                  performed in a single rewrite operation  (to  avoid  loops).   A
           rewriteContext default
           rewriteRule "(.*)<virtualnamingcontext>$" "%1<realnamingcontext>" ":"
           # empty filter rule
           rewriteContext searchFilter
           # all dataflow from server to client
           rewriteContext searchResult
           rewriteRule "(.*)<realnamingcontext>$" "%1<virtualnamingcontext>" ":"
           rewriteContext searchAttrDN alias searchResult
           rewriteContext matchedDN alias searchResult
           # 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'
           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:
           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.
           rewriteContext  addBlanks
           rewriteRule     "(.*),([^ ].*)" "%1, %2"
           # This one eats blanks
           rewriteContext  eatBlanks
           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'
           rewriteContext  default
           rewriteRule     ".*" "%{>addBlanks(%0)}" ":"
           # Rewrite the search base according to 'default' rules.
           rewriteContext  searchBase alias default
           # Search results with OpenLDAP DN are rewritten back with
           # 'dc=home,dc=net' naming context, with spaces eaten.
           rewriteContext  searchResult
           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)
           rewriteMap ldap attr2dn "ldap://host/dc=my,dc=org?dn?sub"
           # 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:
           rewriteContext  bindDN
           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.
           rewriteContext searchFilter
           rewriteRule "(.*\\()uid=([a-z0-9_]+)(\\).*)"
           rewriteRule "[^,]+,ou=admin,dc=home,dc=net"
             "%{*prefix}|(uid=%{*arg})(cn=%{*arg})%{*suffix}" ":@I"
           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.
           rewriteContext searchResult
           rewriteRule ".*,ou=People,dc=example,dc=com" "%0" ":@"
           rewriteRule ".*" "" "#"

    LDAP Proxy resolution (a possible evolution of slapd-ldap(5)):

           In case the rewritten DN is an LDAP URI,  the  operation  is  initiated
           towards  the  host[:port] indicated in the uri, if it does not refer to
           the local server.  E.g.:
             rewriteRule '^cn=root,.*' '%0'                     'G{3}'
             rewriteRule '^cn=[a-l].*' 'ldap://' ':@'
             rewriteRule '^cn=[m-z].*' 'ldap://' ':@'
             rewriteRule '.*'          'ldap://' ':@'
           (Rule 1 is simply there to illustrate the 'G{n}' action; it could  have
           been written:
             rewriteRule '^cn=root,.*' 'ldap://' ':@'


           The following statements have been deprecated and should no  longer  be
           pseudorootdn <substitute DN in case of rootdn bind>
                  Use idassert-bind instead.
           pseudorootpw <substitute password in case of rootdn bind>
                  Use idassert-bind instead.


                  default slapd configuration file


           slapd.conf(5),   slapd-ldap(5),  slapo-pcache(5),  slapd(8),  regex(7),


           Pierangelo Masarati, based on back-ldap by Howard Chu

    OpenLDAP 2.4.40 2014/09/20 SLAPD-META(5)


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