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mod_ldap - Apache HTTP Server Version 2.4
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Apache HTTP Server Version 2.4
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Apache Module mod_ldap
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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
Summary
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.
Topics
Example Configuration
LDAP Connection Pool
LDAP Cache
Using SSL/TLS
SSL/TLS Certificates
Directives
LDAPCacheEntries
LDAPCacheTTL
LDAPConnectionPoolTTL
LDAPConnectionTimeout
LDAPLibraryDebug
LDAPOpCacheEntries
LDAPOpCacheTTL
LDAPReferralHopLimit
LDAPReferrals
LDAPRetries
LDAPRetryDelay
LDAPSharedCacheFile
LDAPSharedCacheSize
LDAPTimeout
LDAPTrustedClientCert
LDAPTrustedGlobalCert
LDAPTrustedMode
LDAPVerifyServerCert
Bugfix checklisthttpd changelogKnown issuesReport a bugSee also
Comments
Example Configuration
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 Connection Pool
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.
LDAP Cache
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 Search/Bind Cache
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.
Operation Caches
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.
Monitoring the Cache
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.
Using SSL/TLS
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 CA and optional client certificates to be used,
as well as the type of encryption to be used on the connection (none, SSL or
TLS/STARTTLS).
# 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 CA_DER "/certs/certfile.der"
<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>
# Establish a TLS LDAP connection on port 389. Requires that
# mod_ldap and mod_authnz_ldap be loaded. Change the
# "yourdomain.example.com" to match your domain.
LDAPTrustedGlobalCert CA_DER "/certs/certfile.der"
<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" TLS
Require valid-user
</Location>
SSL/TLS Certificates
The different LDAP SDKs have widely different methods of setting
and handling both CA and client side certificates.
If you intend to use SSL or TLS, read this section CAREFULLY so as to
understand the differences between configurations on the different LDAP
toolkits supported.
Netscape/Mozilla/iPlanet SDK
CA certificates are specified within a file called cert7.db.
The SDK will not talk to any LDAP server whose certificate was
not signed by a CA specified in this file. If
client certificates are required, an optional key3.db file may
be specified with an optional password. The secmod file can be
specified if required. These files are in the same format as
used by the Netscape Communicator or Mozilla web browsers. The easiest
way to obtain these files is to grab them from your browser
installation.
Client certificates are specified per connection using the
LDAPTrustedClientCert
directive by referring
to the certificate "nickname". An optional password may be
specified to unlock the certificate's private key.
The SDK supports SSL only. An attempt to use STARTTLS will cause
an error when an attempt is made to contact the LDAP server at
runtime.
# Specify a Netscape CA certificate file
LDAPTrustedGlobalCert CA_CERT7_DB "/certs/cert7.db"
# Specify an optional key3.db file for client certificate support
LDAPTrustedGlobalCert CERT_KEY3_DB "/certs/key3.db"
# Specify the secmod file if required
LDAPTrustedGlobalCert CA_SECMOD "/certs/secmod"
<Location "/ldap-status">
SetHandler ldap-status
Require host yourdomain.example.com
Satisfy any
AuthType Basic
AuthName "LDAP Protected"
AuthBasicProvider ldap
LDAPTrustedClientCert CERT_NICKNAME <nickname> [password]
AuthLDAPURL "ldaps://127.0.0.1/dc=example,dc=com?uid?one"
Require valid-user
</Location>
Novell SDK
One or more CA certificates must be specified for the Novell
SDK to work correctly. These certificates can be specified as
binary DER or Base64 (PEM) encoded files.
Note: Client certificates are specified globally rather than per
connection, and so must be specified with the LDAPTrustedGlobalCert
directive as below. Trying to set client certificates via the
LDAPTrustedClientCert
directive will cause an error to be logged
when an attempt is made to connect to the LDAP server.
The SDK supports both SSL and STARTTLS, set using the
LDAPTrustedMode parameter.
If an ldaps:// URL is specified,
SSL mode is forced, override this directive.
# Specify two CA certificate files
LDAPTrustedGlobalCert CA_DER "/certs/cacert1.der"
LDAPTrustedGlobalCert CA_BASE64 "/certs/cacert2.pem"
# Specify a client certificate file and key
LDAPTrustedGlobalCert CERT_BASE64 "/certs/cert1.pem"
LDAPTrustedGlobalCert KEY_BASE64 "/certs/key1.pem" [password]
# Do not use this directive, as it will throw an error
#LDAPTrustedClientCert CERT_BASE64 "/certs/cert1.pem"
OpenLDAP SDK
One or more CA certificates must be specified for the OpenLDAP
SDK to work correctly. These certificates can be specified as
binary DER or Base64 (PEM) encoded files.
Both CA and client certificates may be specified globally
(LDAPTrustedGlobalCert) or
per-connection (LDAPTrustedClientCert).
When any settings are specified per-connection, the global
settings are superseded.
The documentation for the SDK claims to support both SSL and
STARTTLS, however STARTTLS does not seem to work on all versions
of the SDK. The SSL/TLS mode can be set using the
LDAPTrustedMode parameter. If an ldaps:// URL is specified,
SSL mode is forced. The OpenLDAP documentation notes that SSL
(ldaps://) support has been deprecated to be replaced with TLS,
although the SSL functionality still works.
# Specify two CA certificate files
LDAPTrustedGlobalCert CA_DER "/certs/cacert1.der"
LDAPTrustedGlobalCert CA_BASE64 "/certs/cacert2.pem"
<Location "/ldap-status">
SetHandler ldap-status
Require host yourdomain.example.com
LDAPTrustedClientCert CERT_BASE64 "/certs/cert1.pem"
LDAPTrustedClientCert KEY_BASE64 "/certs/key1.pem"
# CA certs respecified due to per-directory client certs
LDAPTrustedClientCert CA_DER "/certs/cacert1.der"
LDAPTrustedClientCert CA_BASE64 "/certs/cacert2.pem"
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>
Solaris SDK
SSL/TLS for the native Solaris LDAP libraries is not yet
supported. If required, install and use the OpenLDAP libraries
instead.
Microsoft SDK
SSL/TLS certificate configuration for the native Microsoft
LDAP libraries is done inside the system registry, and no
configuration directives are required.
Both SSL and TLS are supported by using the ldaps:// URL
format, or by using the LDAPTrustedMode directive accordingly.
Note: The status of support for client certificates is not yet known
for this toolkit.
LDAPCacheEntries Directive
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.
LDAPCacheTTL Directive
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).
LDAPConnectionPoolTTL Directive
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).
LDAPConnectionTimeout Directive
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 10 seconds, if the LDAP client library linked with the
server supports the LDAP_OPT_NETWORK_TIMEOUT option.
LDAPConnectionTimeout is only available when the LDAP client library linked
with the server supports the LDAP_OPT_NETWORK_TIMEOUT
(or LDAP_OPT_CONNECT_TIMEOUT) option, and the ultimate behavior is
dictated entirely by the LDAP client library.
LDAPLibraryDebug Directive
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).
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.
LDAPOpCacheEntries Directive
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.
LDAPOpCacheTTL Directive
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.
LDAPReferralHopLimit Directive
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.
LDAPReferrals Directive
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:
"on"
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.
"off"
When set to "off", the underlying SDK's referral chasing state
is disabled completely.
"default"
When set to "default", the underlying SDK's referral chasing state
is not changed, LDAPReferralHopLimit is not
used to override 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.
LDAPRetries Directive
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.
LDAPRetryDelay Directive
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.
LDAPSharedCacheFile Directive
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.
LDAPSharedCacheSize Directive
Description:Size in bytes of the shared-memory cache
Syntax:LDAPSharedCacheSize bytes
Default:LDAPSharedCacheSize 500000
Context:server config
Status:Extension
Module:mod_ldap
Specifies the number of bytes to allocate for the shared
memory cache. The default is 500kb. If set to 0, shared memory
caching will not be used and every HTTPD process will create its
own cache.
LDAPTimeout Directive
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.
LDAPTrustedClientCert Directive
Description:Sets the file containing or nickname referring to a per
connection client certificate. Not all LDAP toolkits support per
connection client certificates.
Syntax:LDAPTrustedClientCert type directory-path/filename/nickname [password]
Context:directory, .htaccess
Status:Extension
Module:mod_ldap
It specifies the directory path, file name or nickname 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. Some LDAP toolkits (notably Novell)
do not support per connection client certificates, and will throw an
error on LDAP server connection if you try to use this directive
(Use the LDAPTrustedGlobalCert
directive instead for Novell client
certificates - See the SSL/TLS certificate guide above for details).
The type specifies the kind of certificate parameter being
set, depending on the LDAP toolkit being used. Supported types are:
CA_DER - binary DER encoded CA certificate
CA_BASE64 - PEM encoded CA certificate
CERT_DER - binary DER encoded client certificate
CERT_BASE64 - PEM encoded client certificate
CERT_NICKNAME - Client certificate "nickname" (Netscape SDK)
KEY_DER - binary DER encoded private key
KEY_BASE64 - PEM encoded private key
LDAPTrustedGlobalCert Directive
Description:Sets the file or database containing global trusted
Certificate Authority or global client certificates
Syntax:LDAPTrustedGlobalCert type directory-path/filename [password]
Context:server config
Status:Extension
Module:mod_ldap
It specifies the directory path and file 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. Some LDAP toolkits
(notably Novell) require all client certificates to be set globally using
this directive. Most other toolkits require clients certificates to be set
per Directory or per Location using LDAPTrustedClientCert. If you get this
wrong, an error may be logged when an attempt is made to contact the LDAP
server, or the connection may silently fail (See the SSL/TLS certificate
guide above for details).
The type specifies the kind of certificate parameter being
set, depending on the LDAP toolkit being used. Supported types are:
CA_DER - binary DER encoded CA certificate
CA_BASE64 - PEM encoded CA certificate
CA_CERT7_DB - Netscape cert7.db CA certificate database file
CA_SECMOD - Netscape secmod database file
CERT_DER - binary DER encoded client certificate
CERT_BASE64 - PEM encoded client certificate
CERT_KEY3_DB - Netscape key3.db client certificate database file
CERT_NICKNAME - Client certificate "nickname" (Netscape SDK)
CERT_PFX - PKCS#12 encoded client certificate (Novell SDK)
KEY_DER - binary DER encoded private key
KEY_BASE64 - PEM encoded private key
KEY_PFX - PKCS#12 encoded private key (Novell SDK)
LDAPTrustedMode Directive
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:
NONE - no encryption
SSL - ldaps:// encryption on default port 636
TLS - STARTTLS encryption on default port 389
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.
LDAPVerifyServerCert Directive
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.
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