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 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 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 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.
- /etc/ldap/slapd.conf
- default slapd configuration file
Originally implemented by Howard Chu; extended by Pierangelo
Masarati.