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       slapo-chain - chain overlay to slapd




       The  chain  overlay to slapd(8) allows automatic referral chasing.  Any
       time a referral is returned (except for bind operations), it is  chased
       by  using an instance of the ldap backend.  If operations are performed
       with an identity (i.e. after a bind), that  identity  can  be  asserted
       while  chasing the referrals by means of the identity assertion feature
       of back-ldap (see slapd-ldap(5)  for  details),  which  is  essentially
       based  on  the  proxied  authorization  control  [RFC  4370].  Referral
       chasing can be controlled by the client by issuing the chaining control
       (see draft-sermersheim-ldap-chaining for details.)

       The  config  directives  that  are  specific  to  the chain overlay are
       prefixed by  chain-,  to  avoid  potential  conflicts  with  directives
       specific to the underlying database or to other stacked overlays.

       There   are  very  few  chain  overlay  specific  directives;  however,
       directives related to the instances of the ldap  backend  that  may  be
       implicitly  instantiated  by  the  overlay may assume a special meaning
       when used in conjunction with this  overlay.   They  are  described  in
       slapd-ldap(5), and they also need to be prefixed by chain-.

       Note: this overlay is built into the ldap backend; it is not a separate

       overlay chain
              This directive adds the chain overlay to  the  current  backend.
              The chain overlay may be used with any backend, but it is mainly
              intended for use with local storage  backends  that  may  return
              referrals.  It is useless in conjunction with the slapd-ldap and
              slapd-meta backends because they  already  exploit  the  libldap
              specific  referral chase feature.  [Note: this may change in the
              future, as the ldap(5) and  meta(5)  backends  might  no  longer
              chase referrals on their own.]

       chain-cache-uri {FALSE|true}
              This  directive instructs the chain overlay to cache connections
              to URIs parsed out of referrals that are not predefined,  to  be
              reused  for  later  chaining.  These URIs inherit the properties
              configured  for  the   underlying   slapd-ldap(5)   before   any
              occurrence  of  the  chain-uri  directive;  basically,  they are
              chained anonymously.

       chain-chaining [resolve=<r>] [continuation=<c>] [critical]
              This  directive  enables  the  chaining  control   (see   draft-
              sermersheim-ldap-chaining  for details) with the desired resolve
              and  continuation  behaviors  and  criticality.    The   resolve
              parameter  refers  to the behavior while discovering a resource,
              namely when accessing the object indicated by  the  request  DN;
              the continuation parameter refers to the behavior while handling
              intermediate responses, which  is  mostly  significant  for  the
              search operation, but may affect extended operations that return
              intermediate responses.  The values  r  and  c  can  be  any  of
              chainingPreferred,     chainingRequired,     referralsPreferred,
              referralsRequired.  If the critical  flag  affects  the  control
              criticality  if provided.  [This control is experimental and its
              support may change in the future.]

       chain-max-depth <n>
              In case a referral is returned during referral chasing,  further
              chasing  occurs at most <n> levels deep.  Set to 1 (the default)
              to disable further referral chasing.

       chain-return-error {FALSE|true}
              In case referral chasing  fails,  the  real  error  is  returned
              instead  of  the  original  referral.  In case multiple referral
              URIs are present,  only  the  first  error  is  returned.   This
              behavior  may  not  be  always  appropriate nor desirable, since
              failures in referral chasing might be  better  resolved  by  the
              client  (e.g. when caused by distributed authentication issues).

       chain-uri <ldapuri>
              This directive instantiates a new underlying ldap  database  and
              instructs  it about which URI to contact to chase referrals.  As
              opposed to what stated in slapd-ldap(5), only one URI can appear
              after  this  directive;  all subsequent slapd-ldap(5) directives
              prefixed by chain- refer to this specific instance of  a  remote

       Directives  for  configuring  the  underlying ldap database may also be
       required, as shown in this example:

              overlay                 chain
              chain-rebind-as-user    FALSE

              chain-uri               "ldap://"
              chain-rebind-as-user    TRUE
              chain-idassert-bind     bindmethod="simple"

              chain-uri               "ldap://"
              chain-idassert-bind     bindmethod="simple"

       Any  valid  directives  for  the  ldap  database  may  be   used;   see
       slapd-ldap(5)  for  details.   Multiple  occurrences  of  the chain-uri
       directive  may  appear,  to  define  multiple  "trusted"   URIs   where
       operations with identity assertion are chained.  All URIs not listed in
       the  configuration  are   chained   anonymously.    All   slapd-ldap(5)
       directives  appearing  before  the  first  occurrence  of chain-uri are
       inherited by all URIs, unless specifically overridden inside  each  URI


              default slapd configuration file


       slapd.conf(5), slapd-config(5), slapd-ldap(5), slapd(8).


       Originally  implemented by Howard Chu; extended by Pierangelo Masarati.