Provided by: ultrapossum-slapd_0.0.4+2.2.20sb3-1_i386 bug


       slapd-meta - metadirectory backend




       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
       scenarios will be discussed.


       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: as with the ldap backend, operational attributes related to entry
       creation/modification should not be used, as they would  be  passed  to
       the  target  servers,  generating  an error.  Moreover, it makes little
       sense to use such attributes in proxying, as the proxy  server  doesn’t
       actually store data, so it should have no knowledge of such attributes.
       While code to strip the modification attributes has been put  in  place
       (and  #ifdef’d),  it  implies  unmotivated overhead.  So it is strongly
       recommended to set
              lastmod  off
       for every ldap and meta backend.


       Target  configuration  starts  with  the  "uri"  directive.   All   the
       configuration  directives  that  are  not specific to targets should be
       defined first for clarity, including  those  that  are  common  to  all
       backends.  They are:

       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,
              modrdn; 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 {forever|disabled|<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 in seconds is required.


       Target specification starts with a "uri" directive:

       uri <protocol>://[<host>[:<port>]]/<naming context>
              The  "server"  directive  that  was  allowed in the LDAP backend
              (although deprecated) has been discarded in  the  Meta  backend.
              The  <protocol>  part can be anything ldap_initialize(3) accepts
              ({ldap|ldaps|ldapi} and variants);  <host>  and  <port>  may  be
              omitted,  defaulting  to whatever is set in /etc/ldap.conf.  The
              <naming context> part is mandatory.  It must end with one of the
              naming contexts defined for the backend, e.g.:

              suffix "dc=foo,dc=com"
              uri    "ldap://,dc=foo,dc=com"

       The <naming context> part doesn’t need to be unique across the targets;
       it may also  match  one  of  the  values  of  the  "suffix"  directive.
       Multiple  URIs  may  be defined in a single argument.  The URIs must be
       separated by TABs (e.g. ’\t’), and the additional  URIs  must  have  no
       <naming  context>  part.  This causes the underlying library to contact
       the first server of the list that responds.

       default-target [<target>]
              The "default-target" directive can also be  used  during  target
              specification.  With no arguments it marks the current target as
              the default.  The optional number marks target <target>  as  the
              default  one, starting from 1.  Target <target> must be defined.

       binddn <administrative DN for access control purposes>
              This directive, as in the LDAP backend, allows to define the  DN
              that  is  used  to  query the target server for acl checking; it
              should 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.

       bindpw <password for access control purposes>
              This directive sets the password for acl checking in conjunction
              with the above mentioned "binddn" directive.

              If  this  option  is  given,  the  client’s bind credentials are
              remembered for rebinds when chasing referrals.

       pseudorootdn <substitute DN in case of rootdn bind>
              This directive, if present, sets the DN that will be substituted
              to  the  bind DN if a bind with the backend’s "rootdn" succeeds.
              The true "rootdn" of the target server ought  not  be  used;  an
              arbitrary administrative DN should used instead.

       pseudorootpw <substitute password in case of rootdn bind>
              This  directive  sets the credential that will be used in case a
              bind with the backend’s  "rootdn"  succeeds,  and  the  bind  is
              propagated to the target using the "pseudorootdn" DN.

       Note:  cleartext  credentials  must be supplied here; as a consequence,
       using the pseudorootdn/pseudorootpw directives is inherently unsafe.

       rewrite* ...
              The rewrite options are described in the "REWRITING" section.

       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.

       Note: this also fixes a flaw in suffix  massaging,  which  operated  on
       (case  insensitive)  DNs instead of normalized DNs, so "dc=foo, dc=com"
       would not match "dc=foo,dc=com".

       See the "REWRITING" section.

       map {attribute|objectclass} [<local name>|*] {<foreign name>|*}
              This maps object classes and attributes as in the LDAP  backend.
              See slapd-ldap(5).


       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
       "one" search is honored, and  the  scope  is  derated,  only  when  the
       incoming  base  is at most one level lower of a target’s naming context
       (prior to massaging).

       Finally, if the scope is "sub" the incoming base is  replaced  by  each
       target’s unmassaged naming context, and the scope is not altered.

       2b)  Consider  the above reported scenario with the two servers sharing
       the same naming context:

              database      meta
              suffix        "dc=foo,dc=com"

              uri           "ldap://,dc=com"
              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   drop   me   a   note   if  you  can  find  other  exceptions:
       <>).  The rule

              access to dn="<dn>" attr=<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
       enforce additional restrictions to "foo".


       A  string  is  rewritten according to a set of rules, called a ‘rewrite
       context’.  The rules are based on  Regular  Expressions  (POSIX  regex)
       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.

       The underlying concept is to build a lightweight rewrite module for the
       slapd server (initially dedicated to the LDAP backend).


       An incoming string is matched agains 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 behaviorm
       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 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{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.

       More flags (mainly Action Flags) will be added as needed.

Pattern matching:

       See regex(7).

Substitution Pattern Syntax:

       Everything starting with ‘%’ requires substitution;

       the only obvious exception is ‘%%’, which is left as is;

       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);

       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 derefenced 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(7)   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

       client -> server:

              (default)            if defined and no specific context
                                   is available
              bindDN               bind
              searchBase           search
              searchFilter         search
              searchFilterAttrDN   search
              compareDN            compare
              compareAttrDN        compare AVA
              addDN                add
              addAttrDN            add AVA
              modifyDN             modify
              modifyAttrDN         modify AVA
              modrDN               modrdn
              newSuperiorDN        modrdn
              deleteDN             delete
              exopPasswdDN         passwd exop 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 aliase 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
              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.

Configuration examples:

       # set to ‘off’ to disable rewriting
       rewriteEngine on

       # the rules the "suffixmassage" directive implies
       rewriteEngine on
       # all dataflow from client to server referring to DNs
       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"

       # Then we need to detect DN made up of a single email,
       # e.g. ‘’; 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.
       rewriteContext bindDN
       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:
       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://’ ’:@’

       with the advantage of saving one rewrite pass ...)


       The  proxy  cache  overlay  allows  caching  of  LDAP  search  requests
       (queries)  in a local database.  For an incoming query, the proxy cache
       determines its corresponding template. If the template was specified as
       cacheable   using  the  proxytemplate  directive  and  the  request  is
       contained in a cached request, it is answered  from  the  proxy  cache.
       Otherwise,  the  search  is  performed  as  usual  and cacheable search
       results are saved in the cache for use in future queries.

       A template is defined by a filter string and an index identifying a set
       of  attributes.  The  template  string  for  a query can be obtained by
       removing assertion values from  the  RFC  2254  representation  of  its
       search filter. A query belongs to a template if its template string and
       set  of  projected  attributes  correspond  to  a  cacheable  template.
       Examples    of    template    strings   are   (mail=),   (|(sn=)(cn=)),

       The following cache specific directives can be used  to  configure  the
       proxy cache:

       overlay proxycache
              This  directive  adds  the  proxycache  overlay  to  the current
              backend. The proxycache overlay may be used with any backend but
              is intended for use with the ldap and meta backends.

       proxycache   <database>   <max_entries>   <numattrsets>   <entry_limit>
              The  directive  enables proxy caching in the current backend and
              sets general cache parameters. A <database> backend will be used
              internally  to  maintain the cached entries. The chosen database
              will need to be  configured  as  well,  as  shown  below.  Cache
              replacement   is   invoked   when   the   cache  size  grows  to
              <max_entries> entries and continues till the  cache  size  drops
              below this size.  <numattrsets> should be equal to the number of
              following proxyattrset directives. Queries are  cached  only  if
              they  correspond  to  a  cacheable  template  (specified  by the
              proxytemplate directive) and the number of entries  returned  is
              less  than  <entry_limit>.  Consistency check is performed every
              <cc_period> duration (specified in secs). In each cycle  queries
              with  expired  "time  to  live(TTL)" are removed. A sample cache
              configuration is:

              proxycache bdb 10000 1 50 100

       proxyattrset <index> <attrs...>
              Used to associate a set of attributes <attrs..> with an <index>.
              Each  attribute  set  is  associated  with  an integer from 0 to
              <numattrsets>-1. These indices are  used  by  the  proxytemplate
              directive to define cacheable templates.

       proxytemplate <template_string> <attrset_index> <ttl>
              Specifies a cacheable template and "time to live" (in sec) <ttl>
              of queries belonging to the template.

       The following adds a template with  filter  string  (&sn=)(givenName=))
       and  attributes  mail,  postaladdress,  telephonenumber  and a TTL of 1

              proxyattrset 0 mail postaladdress telephonenumber
              proxytemplate (&(sn=)(givenName=)) 0 3600

       Directives for configuring the underlying database must also be  given,
       as shown here:

              directory /var/tmp/cache
              cachesize 100

       Any valid directives for the chosen database type may be used.


              default slapd configuration file


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


       Pierangelo Masarati, based on back-ldap by Howard Chu