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SLAPO-CHAIN(5)		       File Formats Manual		  SLAPO-CHAIN(5)

NAME
     slapo-chain - chain overlay to slapd

SYNOPSIS
     /usr/local/etc/openldap/slapd.conf

DESCRIPTION
     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 iden-
     tity  (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 au-
     thorization 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 un-
     derlying 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 instan-
     tiated 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
     module.

     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 in-
	    tended for use with local storage backends that  may  return  refer-
	    rals.   It	is  useless  in  conjunction  with  the  slapd-ldap  and
	    slapd-meta backends because they already exploit  the  libldap  spe-
	    cific 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 be-
	    havior while discovering a resource, namely when accessing	the  ob-
	    ject  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,  referralsPre-
	    ferred, referralsRequired.	If the critical flag affects the control
	    criticality if provided.  [This control is experimental and its sup-
	    port 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 distrib-
	    uted authentication issues).

     chain-uri <ldapuri>
	    This  directive  instantiates a new underlying ldap database and in-
	    structs it about which URI to contact to chase  referrals.	 As  op-
	    posed 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 server.

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

	    overlay		    chain
	    chain-rebind-as-user    FALSE

	    chain-uri		    "ldap://ldap1.example.com"
	    chain-rebind-as-user    TRUE
	    chain-idassert-bind     bindmethod="simple"
				    binddn="cn=Auth,dc=example,dc=com"
				    credentials="secret"
				    mode="self"

	    chain-uri		    "ldap://ldap2.example.com"
	    chain-idassert-bind     bindmethod="simple"
				    binddn="cn=Auth,dc=example,dc=com"
				    credentials="secret"
				    mode="none"

     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  anony-
     mously.  All slapd-ldap(5) directives appearing before the first occurrence
     of  chain-uri are inherited by all URIs, unless specifically overridden in-
     side each URI configuration.

FILES
     /usr/local/etc/openldap/slapd.conf
	    default slapd configuration file

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

AUTHOR
     Originally implemented by Howard Chu; extended by Pierangelo Masarati.

OpenLDAP 2.6.13 		   2026/03/09			  SLAPO-CHAIN(5)

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