slapd−ldap — LDAP backend to slapd
ETCDIR/slapd.conf
The LDAP backend to slapd(8) is not an actual database; instead it acts as a proxy to forward incoming requests to another LDAP server. While processing requests it will also chase referrals, so that referrals are fully processed instead of being returned to the slapd client.
Sessions that explicitly Bind to the back-ldap database always create their own private connection to the remote LDAP server. Anonymous sessions will share a single anonymous connection to the remote server. For sessions bound through other mechanisms, all sessions with the same DN will share the same connection. This connection pooling strategy can enhance the proxy's efficiency by reducing the overhead of repeatedly making/breaking multiple connections.
The ldap database can also act as an information service,
i.e. the identity of locally authenticated clients is
asserted to the remote server, possibly in some modified
form. For this purpose, the proxy binds to the remote server
with some administrative identity, and, if required,
authorizes the asserted identity. See the idassert−
* rules below.
The administrative identity of the proxy, on the remote
server, must be allowed to authorize by means of appropriate
authzTo
rules; see
slapd.conf(5) for
details.
The proxy instance of slapd(8) must contain schema information for the attributes and objectClasses used in filters, request DNs and request-related data in general. It should also contain schema information for the data returned by the proxied server. It is the responsibility of the proxy administrator to keep the schema of the proxy lined up with that of the proxied server.
Note | |
---|---|
When looping back to the same instance of
slapd(8), each
connection requires a new thread; as a consequence,
the slapd(8) |
These slapd.conf
options apply to the LDAP backend database. That is, they
must follow a "database ldap" line and come before any
subsequent "backend" or "database" lines. Other database
options are described in the slapd.conf(5) manual
page.
Note | |
---|---|
In early versions of back-ldap it was recommended to always set |
lastmod off
for ldap and meta
databases. This was
required because operational attributes related to entry
creation and modification should not be proxied, as they
could be mistakenly written to the target server(s),
generating an error. The current implementation automatically
sets lastmod to off
, so its use is redundant
and should be omitted.
LDAP server to use. Multiple URIs can be set in a
single ldapurl
argument,
resulting in the underlying library automatically
calling the first server of the list that responds,
e.g.
uri "ldap://host/ ldap://backup−host/"
The URI list is space- or comma-separated. Whenever the server that responds is not the first one in the list, the list is rearranged and the responsive server is moved to the head, so that it will be first contacted the next time a connection needs to be created.
acl−bind
bindmethod=simple|sasl
[binddn=<simple DN>] [credentials=<simple
password>] [saslmech=<SASL mech>]
[secprops=<properties>]
[realm=<realm>] [authcId=<authentication ID>]
[authzId=<authorization ID>]
[starttls=no|yes|critical]
[tls_cert=<file>]
[tls_key=<file>]
[tls_cacert=<file>]
[tls_cacertdir=<path>]
[tls_reqcert=never|allow|try|demand]
[tls_reqsan=never|allow|try|demand]
[tls_cipher_suite=<ciphers>]
[tls_ecname=<names>]
[tls_protocol_min=<major>[.<minor>]]
[tls_crlcheck=none|peer|all]
Allows one to define the parameters of the authentication method that is internally used by the proxy to collect info related to access control, and whenever an operation occurs with the identity of the rootdn of the LDAP proxy database. The identity defined by this directive, according to the properties associated to the authentication method, is supposed to have read access on the target server to attributes used on the proxy for ACL checking.
There is no risk of giving away such values; they are only used to check permissions. The default is to use
simple
bind, with emptybinddn
andcredentials
, which means that the related operations will be performed anonymously. If not set, and ifidassert−bind
is defined, this latter identity is used instead. Seeidassert−bind
for details.The connection between the proxy database and the remote server associated to this identity is cached regardless of the lifespan of the client-proxy connection that first established it.
This identity is not implicitly used by the proxy when the client connects anonymously. The
idassert−bind
feature, instead, in some cases can be crafted to implement that behavior, which is intrinsically unsafe and should be used with extreme care.The TLS settings default to the same as the main slapd TLS settings, except for
tls_reqcert
which defaults to "demand", andtls_reqsan
which defaults to "allow".
Defines how to handle operation cancellation. By
default, abandon
is invoked, so
the operation is abandoned immediately. If set to
ignore
, no
action is taken and any further response is ignored;
this may result in further response messages to be
queued for that connection, so it is recommended that
long lasting connections are timed out either by
idle−timeout
or
conn−ttl
, so that
resources eventually get released. If set to exop
, a cancel
operation (RFC
3909) is issued, resulting in the cancellation of the
current operation; the cancel
operation waits
for remote server response, so its use may not be
recommended. If set to exop−discover
,
support of the cancel
extended
operation is detected by reading the remote server's
root DSE.
enable/disable automatic referral chasing, which is
delegated to the underlying libldap, with rebinding
eventually performed if the rebind−as−user
directive is used. The default is to chase
referrals.
This directive defines the maximum size of the privileged connections pool.
This directive causes a cached connection to be dropped and recreated after a given ttl, regardless of being idle or not.
if defined, selects what local
identities are
authorized to exploit the identity assertion feature.
The string <authz-regexp>
mostly follows the rules defined for the authzFrom
attribute.
See slapd.conf(5),
section related to authz−policy
, for
details on the syntax of this field. This parameter
differs from the documented behavior in relation to the
meaning of *, which in this case allows anonymous
rather than denies.
idassert−bind
bindmethod=none|simple|sasl
[binddn=<simple DN>] [credentials=<simple
password>] [saslmech=<SASL mech>]
[secprops=<properties>]
[realm=<realm>] [authcId=<authentication ID>]
[authzId=<authorization ID>]
[authz={native|proxyauthz}]
[mode=<mode>] [flags=<flags>]
[starttls=no|yes|critical]
[tls_cert=<file>]
[tls_key=<file>]
[tls_cacert=<file>]
[tls_cacertdir=<path>]
[tls_reqcert=never|allow|try|demand]
[tls_reqsan=never|allow|try|demand]
[tls_cipher_suite=<ciphers>]
[tls_ecname=<names>]
[tls_protocol_min=<version>]
[tls_crlcheck=none|peer|all]
Allows one to define the parameters of the authentication method that is internally used by the proxy to authorize connections that are authenticated by other databases. Direct binds are always proxied without any idassert handling.
The identity defined by this directive, according to the properties associated to the authentication method, is supposed to have auth access on the target server to attributes used on the proxy for authentication and authorization, and to be allowed to authorize the users. This requires to have
proxyAuthz
privileges on a wide set of DNs, e.g.authzTo=dn.subtree:""
, and the remote server to haveauthz−policy
set toto
orboth
. See slapd.conf(5) for details on these statements and for remarks and drawbacks about their usage. The supported bindmethods are
none|simple|sasl
where
none
is the default, i.e. no identity assertion is performed.The authz parameter is used to instruct the SASL bind to exploit
native
SASL authorization, if available; since connections are cached, this should only be used when authorizing with a fixed identity (e.g. by means of theauthzDN
orauthzID
parameters). Otherwise, the defaultproxyauthz
is used, i.e. the proxyAuthz control (Proxied Authorization, RFC 4370) is added to all operations.The supported modes are:
<mode> := {legacy|anonymous|none|self}
If
<mode>
is not present, andauthzId
is given, the proxy always authorizes that identity. <authorization ID> can be
u:<user>
[dn:]<DN>
The former is supposed to be expanded by the remote server according to the authz rules; see slapd.conf(5) for details. In the latter case, whether or not the
dn:
prefix is present, the string must pass DN validation and normalization.The default mode is
legacy
, which implies that the proxy will either perform a simple bind as theauthcDN
or a SASL bind as theauthcID
and assert the client's identity when it is not anonymous. The other modes imply that the proxy will always either perform a simple bind as theauthcDN
or a SASL bind as theauthcID
, unless restricted byidassert−authzFrom
rules (see below), in which case the operation will fail; eventually, it will assert some other identity according to<mode>
. Other identity assertion modes areanonymous
andself
, which respectively mean that theempty
or theclient
's identity will be asserted;none
, which means that no proxyAuthz control will be used, so theauthcDN
or theauthcID
identity will be asserted. For all modes that require the use of theproxyAuthz
control, on the remote server the proxy identity must have appropriateauthzTo
permissions, or the asserted identities must have appropriateauthzFrom
permissions. Note, however, that the ID assertion feature is mostly useful when the asserted identities do not exist on the remote server.Flags can be
override,[non−]prescriptive,proxy−authz−[non−]critical,dn−{authzid|whoami}
When the
override
flag is used, identity assertion takes place even when the database is authorizing for the identity of the client, i.e. after binding with the provided identity, and thus authenticating it, the proxy performs the identity assertion using the configured identity and authentication method.When the
prescriptive
flag is used (the default), operations fail withinappropriateAuthentication
for those identities whose assertion is not allowed by theidassert−authzFrom
patterns. If thenon−prescriptive
flag is used, operations are performed anonymously for those identities whose assertion is not allowed by theidassert−authzFrom
patterns.When the
proxy−authz−non−critical
flag is used (the default), the proxyAuthz control is not marked as critical, in violation of RFC 4370. Use ofproxy−authz−critical
is recommended.When the
dn−authzid
flag is used, RFC 3829 LDAP Authorization Identity Controls is used to retrieve the identity associated to the SASL identity; when thedn−whoami
flag is used, RFC 4532 LDAP Who am I? Operation is performed after the bind for the same purpose.The TLS settings default to the same as the main slapd TLS settings, except for
tls_reqcert
which defaults to "demand", andtls_reqsan
which defaults to "allow".The identity associated to this directive is also used for privileged operations whenever
idassert−bind
is defined andacl−bind
is not. Seeacl−bind
for details.
- idassert-passthru <authz-regexp>
if defined, selects what
local
identities bypass the identity assertion feature. Those identities need to be known by the remote host. The string<authz-regexp>
follows the rules defined for theauthzFrom
attribute. See slapd.conf(5), section related toauthz−policy
, for details on the syntax of this field.- idle−timeout <time>
This directive causes a cached connection to be dropped an recreated after it has been idle for the specified time.
- keepalive <idle>:<probes>:<interval>
The
keepalive
parameter sets the values ofidle
,probes
, andinterval
used to check whether a socket is alive;idle
is the number of seconds a connection needs to remain idle before TCP starts sending keepalive probes;probes
is the maximum number of keepalive probes TCP should send before dropping the connection;interval
is interval in seconds between individual keepalive probes. Only some systems support the customization of these values; thekeepalive
parameter is ignored otherwise, and system-wide settings are used.- network−timeout <time>
Sets the network timeout value after which poll(2)/select(2) following a connect(2) returns in case of no activity. The value is in seconds, and it can be specified as for
idle−timeout
.- norefs <NO|yes>
If
yes
, do not return search reference responses. By default, they are returned unless request is LDAPv2.- mit-unknown-schema <NO|yes>
If
yes
, do not return objectClasses or attributes that are not known to the local server. The default is to return all schema elements.- noundeffilter <NO|yes>
If
yes
, return success instead of searching if a filter is undefined or contains undefined portions. By default, the search is propagated after replacing undefined portions with(!(objectClass=*))
, which corresponds to the empty result set.- nerr {CONTINUE|stop}
This directive allows one to select the behavior in case an error is returned by the remote server during a search. The default,
continue
, consists in returning success. If the value is set tostop
, the error is returned to the client.- protocol−version {0,2,3}
This directive indicates what protocol version must be used to contact the remote server. If set to 0 (the default), the proxy uses the same protocol version used by the client, otherwise the requested protocol is used. The proxy returns
unwillingToPerform
if an operation that is incompatible with the requested protocol is attempted.- proxy−whoami {NO|yes}
Turns on proxying of the WhoAmI extended operation. If this option is given, back-ldap will replace slapd's original WhoAmI routine with its own. On slapd sessions that were authenticated by back-ldap, the WhoAmI request will be forwarded to the remote LDAP server. Other sessions will be handled by the local slapd, as before. This option is mainly useful in conjunction with Proxy Authorization.
- quarantine <interval>,<num>[;<interval>,<num>[...]]
Turns on quarantine of URIs that returned LDAP_UNAVAILABLE, so that an attempt to reconnect only occurs at given intervals instead of any time a client requests an operation. The pattern is: retry only after at least
interval
seconds elapsed since last attempt, for exactlynum
times; then use the next pattern. Ifnum
for the last pattern is "+
", it retries forever; otherwise, no more retries occur. The process can be restarted by resetting theolcDbQuarantine
attribute of the database entry in the configuration backend.- rebind−as−user {NO|yes}
If this option is given, the client's bind credentials are remembered for rebinds, when trying to re-establish a broken connection, or when chasing a referral, if
chase−referrals
is set toyes
.- session−tracking−request {NO|yes}
Adds session tracking control for all requests. The client's IP and hostname, and the identity associated to each request, if known, are sent to the remote server for informational purposes. This directive is incompatible with setting
protocol−version
to 2.- single−conn {NO|yes}
Discards current cached connection when the client rebinds.
- t−f−support {NO|yes|discover}
enable if the remote server supports absolute filters (see RFC 4526 for details). If set to
discover
, support is detected by reading the remote server's root DSE.- timeout [<op>=]<val> [...]
This directive allows one to set per-operation timeouts. Operations can be
<op> ::= bind, add, delete, modrdn, modify, compare, search
The overall duration of the
search
operation is controlled either by thetimelimit
parameter or by server-side enforced time limits (seetimelimit
andlimits
in slapd.conf(5) for details). Thistimeout
parameter controls how long the target can be irresponsive before the operation is aborted. Timeout is meaningless for the remaining operations,unbind
andabandon
, which do not imply any response, while it is not yet implemented in currently supportedextended
operations. If no operation is specified, the timeoutval
affects all supported operations.
Note If the timelimit is exceeded, the operation is cancelled (according to the
cancel
directive); the protocol does not provide any means to rollback operations, so the client will not be notified about the result of the operation, which may eventually succeeded or not. In case the timeout is exceeded during a bind operation, the connection is destroyed, according to RFC4511.
Note In some cases, this backend may issue binds prior to other operations (e.g. to bind anonymously or with some prescribed identity according to the
idassert−bind
directive). In this case, the timeout of the operation that resulted in the bind is used.tls {none|[try−]start|[try−]propagate|ldaps}
[starttls=no]
[tls_cert=<file>]
[tls_key=<file>]
[tls_cacert=<file>]
[tls_cacertdir=<path>]
[tls_reqcert=never|allow|try|demand]
[tls_reqsan=never|allow|try|demand]
[tls_cipher_suite=<ciphers>]
[tls_ecname=<names>]
[tls_crlcheck=none|peer|all]
Specify TLS settings for regular connections.
If the first parameter is not "none" then this configures the TLS settings to be used for regular connections. The StartTLS extended operation will be used when establishing the connection unless the URI directive protocol scheme is
ldaps://
. In that case this keyword may only be set to "ldaps" and the StartTLS operation will not be used.With
propagate
, the proxy issues StartTLS operation only if the original connection has a TLS layer set up. Thetry−
prefix instructs the proxy to continue operations if the StartTLS operation failed; its use isnot
recommended.The TLS settings default to the same as the main slapd TLS settings, except for
tls_reqcert
which defaults to "demand",tls_reqsan
which defaults to "allow", andstarttls
which is overshadowed by the first keyword and thus ignored.- use−temporary−conn {NO|yes}
when set to
yes
, create a temporary connection whenever competing with other threads for a shared one; otherwise, wait until the shared connection is available.
The ldap backend does not honor
all ACL semantics as described in slapd.access(5). In
general, access checking is delegated to the remote
server(s). Only read
(=r) access to the entry
pseudo-attribute and to
the other attribute values of the entries returned by the
search
operation is
honored, which is performed by the frontend.
The LDAP backend provides basic proxying functionalities
to many overlays. The chain
overlay, described in
slapo-chain(5), and the
translucent
overlay, described in slapo-translucent(5),
deserve a special mention.
Conversely, there are many overlays that are best used in
conjunction with the LDAP backend. The proxycache
overlay allows
caching of LDAP search requests (queries) in a local
database. See slapo-pcache(5) for
details. The rwm
overlay provides DN rewrite and attribute/objectClass mapping
capabilities to the underlying database. See slapo-rwm(5) for
details.