SLAPO-CHAIN(5) File Formats Manual SLAPO-CHAIN(5)
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 chain-
ing 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 implic-
itly 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 module.
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.]
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 continua-
tion 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.]
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.
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).
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 pre-
fixed by chain- refer to this specific instance of a remote server.
Directives for configuring the underlying ldap database may also be required, as shown in this example:
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 configuration.
default slapd configuration file
slapd.conf(5), slapd-config(5), slapd-ldap(5), slapd(8).
Originally implemented by Howard Chu; extended by Pierangelo Masarati.
OpenLDAP 2.4.28 2011/11/24 SLAPO-CHAIN(5)