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341 lines
13 KiB
XML
341 lines
13 KiB
XML
<?xml version="1.0"?>
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<!DOCTYPE modulesynopsis SYSTEM "../style/modulesynopsis.dtd">
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<?xml-stylesheet type="text/xsl" href="../style/manual.en.xsl"?>
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<!--
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Copyright 2002-2004 The Apache Software Foundation
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Licensed under the Apache License, Version 2.0 (the "License");
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you may not use this file except in compliance with the License.
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You may obtain a copy of the License at
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing, software
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distributed under the License is distributed on an "AS IS" BASIS,
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WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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See the License for the specific language governing permissions and
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limitations under the License.
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-->
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<modulesynopsis metafile="mod_ldap.xml.meta">
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<name>mod_ldap</name>
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<description>LDAP connection pooling and result caching services for use
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by other LDAP modules</description>
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<status>Experimental</status>
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<sourcefile>util_ldap.c</sourcefile>
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<identifier>ldap_module</identifier>
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<compatibility>Available in version 2.0.41 and later</compatibility>
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<summary>
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<p>This module was created to improve the performance of
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websites relying on backend connections to LDAP servers. In
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addition to the functions provided by the standard LDAP
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libraries, this module adds an LDAP connection pool and an LDAP
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shared memory cache.</p>
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<p>To enable this module, LDAP support must be compiled into
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apr-util. This is achieved by adding the <code>--with-ldap</code>
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flag to the <code>./configure</code> script when building
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Apache.</p>
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<p>SSL support requires that <module>mod_ldap</module> be linked
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with one of the following LDAP SDKs: <a href="http://www.openldap.org/">
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OpenLDAP SDK</a> (both 1.x and 2.x), <a href="http://developer.novell.com/ndk/cldap.htm">
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Novell LDAP SDK</a> or the <a href="http://www.iplanet.com/downloads/developer/">
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iPlanet(Netscape)</a> SDK.</p>
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</summary>
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<section id="exampleconfig"><title>Example Configuration</title>
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<p>The following is an example configuration that uses
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<module>mod_ldap</module> to increase the performance of HTTP Basic
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authentication provided by <module>mod_auth_ldap</module>.</p>
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<example>
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# Enable the LDAP connection pool and shared<br />
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# memory cache. Enable the LDAP cache status<br />
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# handler. Requires that mod_ldap and mod_auth_ldap<br />
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# be loaded. Change the "yourdomain.example.com" to<br />
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# match your domain.<br />
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<br />
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LDAPSharedCacheSize 200000<br />
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LDAPCacheEntries 1024<br />
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LDAPCacheTTL 600<br />
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LDAPOpCacheEntries 1024<br />
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LDAPOpCacheTTL 600<br />
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<br />
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<Location /ldap-status><br />
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<indent>
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SetHandler ldap-status<br />
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Order deny,allow<br />
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Deny from all<br />
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Allow from yourdomain.example.com<br />
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AuthLDAPEnabled on<br />
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AuthLDAPURL ldap://127.0.0.1/dc=example,dc=com?uid?one<br />
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AuthLDAPAuthoritative on<br />
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require valid-user<br />
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</indent>
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</Location>
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</example>
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</section>
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<section id="pool"><title>LDAP Connection Pool</title>
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<p>LDAP connections are pooled from request to request. This
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allows the LDAP server to remain connected and bound ready for
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the next request, without the need to unbind/connect/rebind.
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The performance advantages are similar to the effect of HTTP
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keepalives.</p>
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<p>On a busy server it is possible that many requests will try
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and access the same LDAP server connection simultaneously.
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Where an LDAP connection is in use, Apache will create a new
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connection alongside the original one. This ensures that the
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connection pool does not become a bottleneck.</p>
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<p>There is no need to manually enable connection pooling in
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the Apache configuration. Any module using this module for
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access to LDAP services will share the connection pool.</p>
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</section>
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<section id="cache"><title>LDAP Cache</title>
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<p>For improved performance, <module>mod_ldap</module> uses an aggressive
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caching strategy to minimize the number of times that the LDAP
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server must be contacted. Caching can easily double or triple
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the throughput of Apache when it is serving pages protected
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with mod_auth_ldap. In addition, the load on the LDAP server
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will be significantly decreased.</p>
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<p><module>mod_ldap</module> supports two types of LDAP caching during
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the search/bind phase with a <em>search/bind cache</em> and
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during the compare phase with two <em>operation
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caches</em>. Each LDAP URL that is used by the server has
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its own set of these three caches.</p>
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<section id="search-bind"><title>The Search/Bind Cache</title>
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<p>The process of doing a search and then a bind is the
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most time-consuming aspect of LDAP operation, especially if
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the directory is large. The search/bind cache is used to
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cache all searches that resulted in successful binds.
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Negative results (<em>i.e.</em>, unsuccessful searches, or searches
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that did not result in a successful bind) are not cached.
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The rationale behind this decision is that connections with
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invalid credentials are only a tiny percentage of the total
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number of connections, so by not caching invalid
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credentials, the size of the cache is reduced.</p>
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<p><module>mod_ldap</module> stores the username, the DN
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retrieved, the password used to bind, and the time of the bind
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in the cache. Whenever a new connection is initiated with the
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same username, <module>mod_ldap</module> compares the password
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of the new connection with the password in the cache. If the
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passwords match, and if the cached entry is not too old,
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<module>mod_ldap</module> bypasses the search/bind phase.</p>
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<p>The search and bind cache is controlled with the <directive
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module="mod_ldap">LDAPCacheEntries</directive> and <directive
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module="mod_ldap">LDAPCacheTTL</directive> directives.</p>
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</section>
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<section id="opcaches"><title>Operation Caches</title>
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<p>During attribute and distinguished name comparison
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functions, <module>mod_ldap</module> uses two operation caches
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to cache the compare operations. The first compare cache is
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used to cache the results of compares done to test for LDAP
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group membership. The second compare cache is used to cache
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the results of comparisons done between distinguished
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names.</p>
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<p>The behavior of both of these caches is controlled with
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the <directive module="mod_ldap">LDAPOpCacheEntries</directive>
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and <directive module="mod_ldap">LDAPOpCacheTTL</directive>
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directives.</p>
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</section>
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<section id="monitoring"><title>Monitoring the Cache</title>
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<p><module>mod_ldap</module> has a content handler that allows
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administrators to monitor the cache performance. The name of
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the content handler is <code>ldap-status</code>, so the
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following directives could be used to access the
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<module>mod_ldap</module> cache information:</p>
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<example>
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<Location /server/cache-info><br />
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<indent>
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SetHandler ldap-status<br />
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</indent>
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</Location>
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</example>
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<p>By fetching the URL <code>http://servername/cache-info</code>,
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the administrator can get a status report of every cache that is used
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by <module>mod_ldap</module> cache. Note that if Apache does not
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support shared memory, then each <code>httpd</code> instance has its
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own cache, so reloading the URL will result in different
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information each time, depending on which <code>httpd</code>
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instance processes the request.</p>
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</section>
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</section>
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<section id="usingssltls"><title>Using SSL</title>
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<p>The ability to create an SSL connections to an LDAP server
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is defined by the directives <directive module="mod_ldap">
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LDAPTrustedCA</directive> and <directive module="mod_ldap">
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LDAPTrustedCAType</directive>. These directives specify the certificate
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file or database and the certificate type. Whenever the LDAP url
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includes <em>ldaps://</em>, <module>mod_ldap</module> will establish
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a secure connection to the LDAP server.</p>
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<example>
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# Establish an SSL LDAP connection. Requires that <br />
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# mod_ldap and mod_auth_ldap be loaded. Change the <br />
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# "yourdomain.example.com" to match your domain.<br />
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<br />
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LDAPTrustedCA /certs/certfile.der<br />
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LDAPTrustedCAType DER_FILE<br />
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<br />
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<Location /ldap-status><br />
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<indent>
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SetHandler ldap-status<br />
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Order deny,allow<br />
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Deny from all<br />
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Allow from yourdomain.example.com<br />
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AuthLDAPEnabled on<br />
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AuthLDAPURL ldaps://127.0.0.1/dc=example,dc=com?uid?one<br />
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AuthLDAPAuthoritative on<br />
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require valid-user<br />
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</indent>
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</Location>
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</example>
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<p>If <module>mod_ldap</module> is linked against the
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Netscape/iPlanet LDAP SDK, it will not talk to any SSL server
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unless that server has a certificate signed by a known Certificate
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Authority. As part of the configuration
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<module>mod_ldap</module> needs to be told where it can find
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a database containing the known CAs. This database is in the same
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format as Netscape Communicator's <code>cert7.db</code>
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database. The easiest way to get this file is to start up a fresh
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copy of Netscape, and grab the resulting
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<code>$HOME/.netscape/cert7.db</code> file.</p>
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</section>
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<directivesynopsis>
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<name>LDAPSharedCacheSize</name>
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<description>Size in bytes of the shared-memory cache</description>
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<syntax>LDAPSharedCacheSize <var>bytes</var></syntax>
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<default>LDAPSharedCacheSize 102400</default>
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<contextlist><context>server config</context></contextlist>
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<usage>
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<p>Specifies the number of bytes to allocate for the shared
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memory cache. The default is 100kb. If set to 0, shared memory
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caching will not be used.</p>
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</usage>
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</directivesynopsis>
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<directivesynopsis>
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<name>LDAPSharedCacheFile</name>
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<description>Sets the shared memory chache file</description>
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<syntax>LDAPSharedCacheFile <var>directory-path/filename</var></syntax>
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<contextlist><context>server config</context></contextlist>
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<usage>
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<p>Specifies the directory path and file name of the shared memory
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cache file. If not set, shared memory caching will not be used.</p>
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</usage>
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</directivesynopsis>
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<directivesynopsis>
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<name>LDAPCacheEntries</name>
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<description>Maximum number of entries in the primary LDAP cache</description>
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<syntax>LDAPCacheEntries <var>number</var></syntax>
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<default>LDAPCacheEntries 1024</default>
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<contextlist><context>server config</context></contextlist>
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<usage>
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<p>Specifies the maximum size of the primary LDAP cache. This
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cache contains successful search/binds. Set it to 0 to turn off
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search/bind caching. The default size is 1024 cached
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searches.</p>
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</usage>
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</directivesynopsis>
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<directivesynopsis>
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<name>LDAPCacheTTL</name>
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<description>Time that cached items remain valid</description>
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<syntax>LDAPCacheTTL <var>seconds</var></syntax>
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<default>LDAPCacheTTL 600</default>
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<contextlist><context>server config</context></contextlist>
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<usage>
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<p>Specifies the time (in seconds) that an item in the
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search/bind cache remains valid. The default is 600 seconds (10
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minutes).</p>
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</usage>
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</directivesynopsis>
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<directivesynopsis>
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<name>LDAPOpCacheEntries</name>
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<description>Number of entries used to cache LDAP compare
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operations</description>
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<syntax>LDAPOpCacheEntries <var>number</var></syntax>
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<default>LDAPOpCacheEntries 1024</default>
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<contextlist><context>server config</context></contextlist>
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<usage>
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<p>This specifies the number of entries <module>mod_ldap</module>
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will use to cache LDAP compare operations. The default is 1024
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entries. Setting it to 0 disables operation caching.</p>
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</usage>
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</directivesynopsis>
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<directivesynopsis>
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<name>LDAPOpCacheTTL</name>
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<description>Time that entries in the operation cache remain
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valid</description>
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<syntax>LDAPOpCacheTTL <var>seconds</var></syntax>
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<default>LDAPOpCacheTTL 600</default>
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<contextlist><context>server config</context></contextlist>
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<usage>
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<p>Specifies the time (in seconds) that entries in the
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operation cache remain valid. The default is 600 seconds.</p>
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</usage>
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</directivesynopsis>
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<directivesynopsis>
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<name>LDAPTrustedCA</name>
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<description>Sets the file containing the trusted Certificate Authority certificate or database</description>
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<syntax>LDAPTrustedCA <var>directory-path/filename</var></syntax>
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<contextlist><context>server config</context></contextlist>
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<usage>
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<p>It specifies the directory path and file name of the trusted CA
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<module>mod_ldap</module> should use when establishing an SSL
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connection to an LDAP server. If using the Netscape/iPlanet Directory
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SDK, the file name should be <code>cert7.db</code>.</p>
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</usage>
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</directivesynopsis>
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<directivesynopsis>
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<name>LDAPTrustedCAType</name>
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<description>Specifies the type of the Certificate Authority file</description>
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<syntax>LDAPTrustedCAType <var>type</var></syntax>
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<contextlist><context>server config</context></contextlist>
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<usage>
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<p>The following types are supported:<br />
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DER_FILE - file in binary DER format<br />
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BASE64_FILE - file in Base64 format<br />
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CERT7_DB_PATH - Netscape certificate database file ")</p>
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</usage>
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</directivesynopsis>
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</modulesynopsis>
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