slapo-chain — chain overlay to slapd
ETCDIR/slapd.conf
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−.
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.
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.]
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 prefixed 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:
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 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.