Apache HTTP Server Version 2.4
Apache HTTP Server Version 2.4
| Description: | LDAP connection pooling and result caching services for use by other LDAP modules |
|---|---|
| Status: | Extension |
| Module Identifier: | ldap_module |
| Source File: | util_ldap.c |
This module was created to improve the performance of websites relying on backend connections to LDAP servers. In addition to the functions provided by the standard LDAP libraries, this module adds an LDAP connection pool and an LDAP shared memory cache.
To enable this module, LDAP support must be compiled into
apr-util. This is achieved by adding the --with-ldap
flag to the configure script when building
Apache.
SSL/TLS support is dependent on which LDAP toolkit has been linked to APR. As of this writing, APR-util supports: OpenLDAP SDK (2.x or later), Novell LDAP SDK, Mozilla LDAP SDK, native Solaris LDAP SDK (Mozilla based) or the native Microsoft LDAP SDK. See the APR website for details.
LDAPCacheEntries LDAPCacheTTL LDAPConnectionPoolTTL LDAPConnectionTimeout LDAPLibraryDebug LDAPOpCacheEntries LDAPOpCacheTTL LDAPReferralHopLimit LDAPReferrals LDAPRetries LDAPRetryDelay LDAPSharedCacheFile LDAPSharedCacheSize LDAPSSLProtocol LDAPTimeout LDAPTrustedClientCert LDAPTrustedGlobalCert LDAPTrustedMode LDAPVerifyServerCert
The following is an example configuration that uses
mod_ldap to increase the performance of HTTP Basic
authentication provided by mod_authnz_ldap.
# Enable the LDAP connection pool and shared
# memory cache. Enable the LDAP cache status
# handler. Requires that mod_ldap and mod_authnz_ldap
# be loaded. Change the "yourdomain.example.com" to
# match your domain.
LDAPSharedCacheSize 500000
LDAPCacheEntries 1024
LDAPCacheTTL 600
LDAPOpCacheEntries 1024
LDAPOpCacheTTL 600
<Location "/ldap-status">
SetHandler ldap-status
Require host yourdomain.example.com
Satisfy any
AuthType Basic
AuthName "LDAP Protected"
AuthBasicProvider ldap
AuthLDAPURL "ldap://127.0.0.1/dc=example,dc=com?uid?one"
Require valid-user
</Location>
LDAP connections are pooled from request to request. This allows the LDAP server to remain connected and bound ready for the next request, without the need to unbind/connect/rebind. The performance advantages are similar to the effect of HTTP keepalives.
On a busy server it is possible that many requests will try and access the same LDAP server connection simultaneously. Where an LDAP connection is in use, Apache will create a new connection alongside the original one. This ensures that the connection pool does not become a bottleneck.
There is no need to manually enable connection pooling in the Apache configuration. Any module using this module for access to LDAP services will share the connection pool.
LDAP connections can keep track of the ldap client
credentials used when binding to an LDAP server. These
credentials can be provided to LDAP servers that do not
allow anonymous binds during referral chasing. To control
this feature, see the
LDAPReferrals and
LDAPReferralHopLimit
directives. By default, this feature is enabled.
For improved performance, mod_ldap uses an aggressive
caching strategy to minimize the number of times that the LDAP
server must be contacted. Caching can easily double or triple
the throughput of Apache when it is serving pages protected
with mod_authnz_ldap. In addition, the load on the LDAP server
will be significantly decreased.
mod_ldap supports two types of LDAP caching during
the search/bind phase with a search/bind cache and
during the compare phase with two operation
caches. Each LDAP URL that is used by the server has
its own set of these three caches.
The process of doing a search and then a bind is the most time-consuming aspect of LDAP operation, especially if the directory is large. The search/bind cache is used to cache all searches that resulted in successful binds. Negative results (i.e., unsuccessful searches, or searches that did not result in a successful bind) are not cached. The rationale behind this decision is that connections with invalid credentials are only a tiny percentage of the total number of connections, so by not caching invalid credentials, the size of the cache is reduced.
mod_ldap stores the username, the DN
retrieved, the password used to bind, and the time of the bind
in the cache. Whenever a new connection is initiated with the
same username, mod_ldap compares the password
of the new connection with the password in the cache. If the
passwords match, and if the cached entry is not too old,
mod_ldap bypasses the search/bind phase.
The search and bind cache is controlled with the LDAPCacheEntries and LDAPCacheTTL directives.
During attribute and distinguished name comparison
functions, mod_ldap uses two operation caches
to cache the compare operations. The first compare cache is
used to cache the results of compares done to test for LDAP
group membership. The second compare cache is used to cache
the results of comparisons done between distinguished
names.
Note that, when group membership is being checked, any sub-group comparison results are cached to speed future sub-group comparisons.
The behavior of both of these caches is controlled with
the LDAPOpCacheEntries
and LDAPOpCacheTTL
directives.
mod_ldap has a content handler that allows
administrators to monitor the cache performance. The name of
the content handler is ldap-status, so the
following directives could be used to access the
mod_ldap cache information:
<Location "/server/cache-info">
SetHandler ldap-status
</Location>
By fetching the URL http://servername/cache-info,
the administrator can get a status report of every cache that is used
by mod_ldap cache. Note that if Apache does not
support shared memory, then each httpd instance has its
own cache, so reloading the URL will result in different
information each time, depending on which httpd
instance processes the request.
The ability to create an SSL and TLS connections to an LDAP server
is defined by the directives
LDAPTrustedGlobalCert,
LDAPTrustedClientCert
and LDAPTrustedMode.
These directives specify the key database and optionally specify the client
certificate(s) to be used, as well as the type of encryption to be used on the
connection (none, or SSL).
# Establish an SSL LDAP connection on port 636. Requires that
# mod_ldap and mod_authnz_ldap be loaded. Change the
# "yourdomain.example.com" to match your domain.
LDAPTrustedGlobalCert CMS_KEYFILE /certs/certfile.kdb
<Location "/ldap-status">
SetHandler ldap-status
Require host yourdomain.example.com
Satisfy any
AuthType Basic
AuthName "LDAP Protected"
AuthBasicProvider ldap
AuthLDAPURL "ldaps://127.0.0.1/dc=example,dc=com?uid?one"
Require valid-user
</Location>
Different LDAP SDKs provide support for certificates in different ways. This has required that the LDAP configuration directives be flexible, and potentially confusing, since they must offer more options than any single SDK can use.
The IBM HTTP Server uses an LDAP SDK that provides certificate support via CMS based key database files and SAF keyrings (on z/OS) that can contain multiple client and CA signer certificates. This key storage will be referred to as key databases throughout the remainder of this documentation.
The LDAPTrustedGlobalCert
directive specifies the key database to be used globally across all LDAP
controlled resources. This key database contains certificates for trusted
issuers and zero or more personal certificates (also called private keys
or client certificates).
The LDAPTrustedClientCert
directive is used to specify the label of the client certificate that
IBM HTTP Server will provide to the LDAP server, if the LDAP sever requests
a certificate. Each protected resource can specify its own
LDAPTrustedClientCert label value.
If the key database designates a default certificate which you wish to
use, or your LDAP server does not request a client certificate, you don't need
to specify LDAPTrustedClientCert.
# Establish an SSL LDAP connection on port 636 using a specific
# certificate and requiring a specific group memership to protect
# a directory. Requires that mod_ldap and mod_authnz_ldap be
# loaded. Change the "yourdomain.example.com", certfile info,
# Directory information, and LDAPURL to match your information.
LDAPTrustedGlobalCert CMS_KEYFILE /certs/certfile.kdb
LDAPTrustedMode SSL
<Directory "/special/protected/info">
AuthLDAPURL ldaps://127.0.0.1:636/dc=example,dc=com?uid?one
# LDAPTrustedClientCert is only required if you want to use a
# non-default cert label.
LDAPTrustedClientCert CMS_LABEL alternate_cert
AuthBasicProvider ldap
AuthLDAPBindDN "cn=ldaptestadm,ou=test group,o=myorg,c=US"
AuthLDAPBindPassword test
AuthName "Protected info"
AuthType Basic
Require ldap-group cn=Just_testers_group,o=Humans,c=us
Satisfy Any
Require host yourdomain.example.com
</Directory>
| Description: | Maximum number of entries in the primary LDAP cache |
|---|---|
| Syntax: | LDAPCacheEntries number |
| Default: | LDAPCacheEntries 1024 |
| Context: | server config |
| Status: | Extension |
| Module: | mod_ldap |
Specifies the maximum size of the primary LDAP cache. This cache contains successful search/binds. Set it to 0 to turn off search/bind caching. The default size is 1024 cached searches.
| Description: | Time that cached items remain valid |
|---|---|
| Syntax: | LDAPCacheTTL seconds |
| Default: | LDAPCacheTTL 600 |
| Context: | server config |
| Status: | Extension |
| Module: | mod_ldap |
Specifies the time (in seconds) that an item in the search/bind cache remains valid. The default is 600 seconds (10 minutes).
| Description: | Discard backend connections that have been sitting in the connection pool too long |
|---|---|
| Syntax: | LDAPConnectionPoolTTL n |
| Default: | LDAPConnectionPoolTTL -1 |
| Context: | server config, virtual host |
| Status: | Extension |
| Module: | mod_ldap |
| Compatibility: | Apache HTTP Server 2.3.12 and later |
Specifies the maximum age, in seconds, that a pooled LDAP connection can remain idle and still be available for use. Connections are cleaned up when they are next needed, not asynchronously.
A setting of 0 causes connections to never be saved in the backend connection pool. The default value of -1, and any other negative value, allows connections of any age to be reused.
For performance reasons, the reference time used by this directive is based on when the LDAP connection is returned to the pool, not the time of the last successful I/O with the LDAP server.
Since 2.4.10, new measures are in place to avoid the reference time from being inflated by cache hits or slow requests. First, the reference time is not updated if no backend LDAP conncetions were needed. Second, the reference time uses the time the HTTP request was received instead of the time the request is completed.
This timeout defaults to units of seconds, but accepts suffixes for milliseconds (ms), minutes (min), and hours (h).
| Description: | Specifies the socket connection timeout in seconds |
|---|---|
| Syntax: | LDAPConnectionTimeout seconds |
| Context: | server config |
| Status: | Extension |
| Module: | mod_ldap |
This directive configures the LDAP_OPT_NETWORK_TIMEOUT (or LDAP_OPT_CONNECT_TIMEOUT) option in the underlying LDAP client library, when available. This value typically controls how long the LDAP client library will wait for the TCP connection to the LDAP server to complete.
If a connection is not successful with the timeout period, either an error will be
returned or the LDAP client library will attempt to connect to a secondary LDAP
server if one is specified (via a space-separated list of hostnames in the
AuthLDAPURL).
The default is 5 seconds in IBM HTTP Server
| Description: | Enable debugging in the LDAP SDK |
|---|---|
| Syntax: | LDAPLibraryDebug 7 |
| Default: | disabled |
| Context: | server config |
| Status: | Extension |
| Module: | mod_ldap |
Turns on SDK-specific LDAP debug options that generally cause the LDAP SDK to log verbose trace information to the main Apache error log. The trace messages from the LDAP SDK provide gory details that can be useful during debugging of connectivity problems with backend LDAP servers
This option is only configurable when Apache HTTP Server is linked with
an LDAP SDK that implements LDAP_OPT_DEBUG or
LDAP_OPT_DEBUG_LEVEL, such as OpenLDAP (a value of 7 is verbose)
or Tivoli Directory Server (a value of 65535 is verbose, on z/OS use 2147483647).
The logged information will likely contain plaintext credentials being used or validated by LDAP authentication, so care should be taken in protecting and purging the error log when this directive is used.
On z/OS, LDAP_OPT_DEBUG messages are written to stdout which will be lost.
To save these messages, set native environment variable LDAP_DEBUG_FILENAME. Be sure to
include a '%' in the filename to create unique output per process.
| Description: | Number of entries used to cache LDAP compare operations |
|---|---|
| Syntax: | LDAPOpCacheEntries number |
| Default: | LDAPOpCacheEntries 1024 |
| Context: | server config |
| Status: | Extension |
| Module: | mod_ldap |
This specifies the number of entries mod_ldap
will use to cache LDAP compare operations. The default is 1024
entries. Setting it to 0 disables operation caching.
| Description: | Time that entries in the operation cache remain valid |
|---|---|
| Syntax: | LDAPOpCacheTTL seconds |
| Default: | LDAPOpCacheTTL 600 |
| Context: | server config |
| Status: | Extension |
| Module: | mod_ldap |
Specifies the time (in seconds) that entries in the operation cache remain valid. The default is 600 seconds.
| Description: | The maximum number of referral hops to chase before terminating an LDAP query. |
|---|---|
| Syntax: | LDAPReferralHopLimit number |
| Default: | SDK dependent, typically between 5 and 10 |
| Context: | directory, .htaccess |
| Override: | AuthConfig |
| Status: | Extension |
| Module: | mod_ldap |
This directive, if enabled by the LDAPReferrals directive,
limits the number of referral hops that are followed before terminating an
LDAP query.
Support for this tunable is uncommon in LDAP SDKs.
| Description: | Enable referral chasing during queries to the LDAP server. |
|---|---|
| Syntax: | LDAPReferrals On|Off|default |
| Default: | LDAPReferrals On |
| Context: | directory, .htaccess |
| Override: | AuthConfig |
| Status: | Extension |
| Module: | mod_ldap |
| Compatibility: | The default parameter is available in Apache 2.4.7 and later |
Some LDAP servers divide their directory among multiple domains and use referrals to direct a client when a domain boundary is crossed. This is similar to a HTTP redirect. LDAP client libraries may or may not chase referrals by default. This directive explicitly configures the referral chasing in the underlying SDK.
LDAPReferrals takes the following values:
When set to "on", the underlying SDK's referral chasing state
is enabled, LDAPReferralHopLimit is used to
override the SDK's hop limit, and an LDAP rebind callback is
registered.
When set to "off", the underlying SDK's referral chasing state is disabled completely.
When set to "default", the underlying SDK's referral chasing state
is not changed, LDAPReferralHopLimit is not
used to overide the SDK's hop limit, and no LDAP rebind callback is
registered.
The directive LDAPReferralHopLimit works in conjunction with
this directive to limit the number of referral hops to follow before terminating the LDAP query.
When referral processing is enabled by a value of "On", client credentials will be provided,
via a rebind callback, for any LDAP server requiring them.
| Description: | Configures the number of LDAP server retries. |
|---|---|
| Syntax: | LDAPRetries number-of-retries |
| Default: | LDAPRetries 3 |
| Context: | server config |
| Status: | Extension |
| Module: | mod_ldap |
The server will retry failed LDAP requests up to
LDAPRetries times. Setting this
directive to 0 disables retries.
LDAP errors such as timeouts and refused connections are retryable.
| Description: | Configures the delay between LDAP server retries. |
|---|---|
| Syntax: | LDAPRetryDelay seconds |
| Default: | LDAPRetryDelay 0 |
| Context: | server config |
| Status: | Extension |
| Module: | mod_ldap |
If LDAPRetryDelay is set to a non-zero
value, the server will delay retrying an LDAP request for the
specified amount of time. Setting this directive to 0 will
result in any retry to occur without delay.
LDAP errors such as timeouts and refused connections are retryable.
| Description: | Sets the shared memory cache file |
|---|---|
| Syntax: | LDAPSharedCacheFile directory-path/filename |
| Context: | server config |
| Status: | Extension |
| Module: | mod_ldap |
Specifies the directory path and file name of the shared memory cache file. If not set, anonymous shared memory will be used if the platform supports it.
| Description: | Size in bytes of the shared-memory cache |
|---|---|
| Syntax: | LDAPSharedCacheSize bytes |
| Default: | 4MB |
| Context: | server config |
| Status: | Extension |
| Module: | mod_ldap |
Specifies the number of bytes to allocate for the shared memory cache. The default is 4MB. If set to 0, shared memory caching will not be used and every HTTPD process will create its own cache.
| Description: | Set SSL protocosl for LDAP connection |
|---|---|
| Syntax: | LDAPSSLProtocol SSLV3,TLS10,TLS11,TLS12,TLS13 |
| Default: | see usage |
| Context: | server config |
| Status: | Extension |
| Module: | mod_ldap |
| Compatibility: | not supported on zOS. Requires PH55900 |
This directive overrides the LDAP SDKs default LDAP SSL protocols. The value is a comma separated list of protocols.
On z/OS, LDAP SSL protocols can only be controlled by the underling System SSL environment variables. The environment variables used to enable or disable SSL protocols will be ignored in the SSL environment used by the rest of the server. See https://www.ibm.com/docs/en/zos/2.5.0?topic=routines-ldap-ssl-client-init for your release for more details.
| Description: | Specifies the timeout for LDAP search and bind operations, in seconds |
|---|---|
| Syntax: | LDAPTimeout seconds |
| Default: | LDAPTimeout 60 |
| Context: | server config |
| Status: | Extension |
| Module: | mod_ldap |
| Compatibility: | Apache HTTP Server 2.3.5 and later |
This directive configures the timeout for bind and search operations, as well as the LDAP_OPT_TIMEOUT option in the underlying LDAP client library, when available.
If the timeout expires, httpd will retry in case an existing connection has been silently dropped by a firewall. However, performance will be much better if the firewall is configured to send TCP RST packets instead of silently dropping packets.
Timeouts for ldap compare operations requires an SDK with LDAP_OPT_TIMEOUT, such as OpenLDAP >= 2.4.4.
| Description: | Sets the label referring to a per connection client certificate. |
|---|---|
| Syntax: | LDAPTrustedClientCert type label |
| Context: | server config, virtual host, directory, .htaccess |
| Status: | Extension |
| Module: | mod_ldap |
Specifies the label of a per connection client certificate used when establishing an SSL or TLS connection to an LDAP server. Different locations or directories may have their own independent client certificate settings.
For the first argument, certificate type, the only value supported by the IBM HTTP Server is CMS_LABEL. CMS_LABEL can be used with both the CMS_KEYFILE or SAF key database types.
The second argument identifies the label associated with the personal (client)
certificate you wish to use from the key database specified in the
LDAPTrustedGlobalCert directive.
This directive is not required if the LDAP server does not request a client certificate, or if you wish to use the client certificate designated as the default in the key database.
| Description: | Sets the file or database containing global trusted Certificate Authority and/or global client certificates |
|---|---|
| Syntax: | LDAPTrustedGlobalCert type key_database_name [password] |
| Context: | server config |
| Status: | Extension |
| Module: | mod_ldap |
Specifies the directory path and file name or keyring name of the trusted CA
certificates and/or system wide client certificates mod_ldap
should use when establishing an SSL or TLS connection to an LDAP
server. Note that all certificate information specified using this directive
is applied globally to the entire server installation and only one key database
can be specified per configuration file.
The type indicates the kind of certificate storage being specified. The only supported types for the IBM HTTP Server are the CMS_KEYFILE type (all platforms) and the SAF type (z/OS only).
The key_database_name specifies the path and filename of a CMS key database or specifies the SAF keyring name. A CMS key database file or a SAF keyring contain a collection of CA signer certificates and zero or more client certificates.
For the SAF type, a password should not be provided, as SAF keyrings do not use a password. Providing a password with the SAF type will result in an initialization failure.
For the CMS_KEYFILE type, you can omit the password and mod_ldap will
try to use a stashed password as generated by ikeyman. The file with the stashed password
must have the same path and basename as the CMS_KEYFILE, but have an extension of ".sth".
Use of the stash file instead of the password is recommended.
If you provide the password in httpd.conf, take extra care to restrict access to the configuration file to protect the password.
See the LDAPTrustedClientCert
directive for information about how to specify the use of a particular
client certificate within a protected resource such as a Directory or
Location container.
| Description: | Specifies the SSL/TLS mode to be used when connecting to an LDAP server. |
|---|---|
| Syntax: | LDAPTrustedMode type |
| Context: | server config, virtual host |
| Status: | Extension |
| Module: | mod_ldap |
The following modes are supported:
Not all LDAP toolkits support all the above modes. An error message will be logged at runtime if a mode is not supported, and the connection to the LDAP server will fail.
If an ldaps:// URL is specified, the mode becomes SSL and the setting of LDAPTrustedMode is ignored.
| Description: | Force server certificate verification |
|---|---|
| Syntax: | LDAPVerifyServerCert On|Off |
| Default: | LDAPVerifyServerCert On |
| Context: | server config |
| Status: | Extension |
| Module: | mod_ldap |
Specifies whether to force the verification of a server certificate when establishing an SSL connection to the LDAP server.