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SLAPD-META(5)                 File Formats Manual                SLAPD-META(5)

       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 scenar-
       ios 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 configu-
       ration  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, 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 {forever|disabled|<&lt;ttl>&gt;}
              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 <&lt;protocol>&gt;://[<&lt;host>&gt;[:<&lt;port>&gt;]]/<&lt;naming context>&gt;
              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://x.foo.com/dc=x,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.   Multi-
       ple  URIs  may be defined in a single argument.  The URIs must be sepa-
       rated 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 [<&lt;target>&gt;]
              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 <&lt;administrative DN for access control purposes>&gt;
              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 <&lt;password for access control purposes>&gt;
              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 <&lt;substitute DN in case of rootdn bind>&gt;
              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 <&lt;substitute password in case of rootdn bind>&gt;
              This directive sets the credential that will be used in  case  a
              bind with the backend's "rootdn" succeeds, and the bind is prop-
              agated 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 <&lt;virtual naming context>&gt; <&lt;real naming context>&gt;
              All  the directives starting with "rewrite" refer to the rewrite
              engine that has been added to slapd.  The "suffixmassage" direc-
              tive  was introduced in the LDAP backend to allow suffix massag-
              ing 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.

       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} [<&lt;local name>&gt;|*] {<&lt;foreign name>&gt;|*}
              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 amaz-
       ingly 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://a.foo.com/dc=a,dc=foo,dc=com"
              uri      "ldap://b.foo.com/dc=b,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 mul-
       tiple 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://a.bar.com/dc=a,dc=foo,dc=com"
              suffixmassage "dc=a,dc=foo,dc=com" "dc=bar,dc=org"

              uri           "ldap://b.foo.com/dc=b,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  tar-
       get'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

       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://a.bar.com/dc=foo,dc=com"
              suffixmassage "dc=foo,dc=com" "dc=bar,dc=org"

              uri           "ldap://b.foo.com/dc=foo,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 configura-
       tions 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 consid-

       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 possi-
       ble 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:  <andoATopenldap.org>).
       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  inter-
       vention  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; extensions are planned to allow basic variable
       substitution and map resolution of substrings.  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 match pattern, a substitution pattern and a set of actions.  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.

Pattern Matching Flags
       `C'    honors case in matching (default is case insensitive)

       `R'    use POSIX Basic Regular Expressions (default is Extended)

Action Flags
       `:'    apply the rule once only (default is recursive)

       `@'    stop applying rules in case of match.

       `#'    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.

       The  ordering of the flags is 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 thwo 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:

       >&gt;      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.)

       &&amp;      variable  assignment;  <name>  defines a variable in the running
              operation structure which can be dereferenced later; operator  &&amp;
              assigns  a  variable  in  the rewrite context scope; operator &&amp;&&amp;
              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 param-
              eter; 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 conse-
       quence, 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  con-
       text  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
              compareDn      compare
              addDn          add
              modifyDn       modify
              modrDn         modrdn
              newSuperiorDn  modrdn
              deleteDn       delete

       server -> client:

              searchResult   search (only if defined; no default;
                             acts on DN and DN-syntax attributes
                             of search results)
              matchedDn      all ops (only if defined; no default;
                             NOT IMPL. except in search)

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 <&lt;context name>&gt; [ alias <&lt;aliased context name>&gt; ]
              <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 <&lt;regex pattern>&gt; <&lt;substitution pattern>&gt; [ <&lt;flags>&gt; ]
              Determines how a tring can be rewritten if a pattern is matched.
              Examples are reported below.

Additional configuration syntax:
       rewriteMap <&lt;map name>&gt; <&lt;map type>&gt; [ <&lt;map attrs>&gt; ]
              Allows to define a map that transforms substring rewriting  into
              something  else.   The map is referenced inside the substitution
              pattern of a rule.

       rewriteParam <&lt;param name>&gt; <&lt;param value>&gt;
              Sets a value with global scope, that can be dereferenced by  the
              command `%{$paramName}'.

       rewriteMaxPasses <&lt;number of passes>&gt;
              Sets  the  maximum  number of total rewriting passes that can be
              performed in a single rewrite operation (to avoid loops).

Configuration examples:
       # set to `off' to disable rewriting
       rewriteEngine on

       # 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. `mail=someoneATexample.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.
       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}" ":"

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://ldap1.my.org/%0' '@'
         rewriteRule '^cn=[m-z].*' 'ldap://ldap2.my.org/%0' '@'
         rewriteRule '.*'          'ldap://ldap3.my.org/%0' '@'

       (Rule 1 is simply there to illustrate the `G{n}' action; it could  have
       been written:

         rewriteRule '^cn=root,.*' 'ldap://ldap3.my.org/%0' '@'

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

              default slapd configuration file

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

OpenLDAP 2.1.22                   06-26-2003                     SLAPD-META(5)