
<!DOCTYPE modulesynopsis SYSTEM "../style/modulesynopsis.dtd">
<?xml-stylesheet type="text/xsl" href="../style/manual.en.xsl"?>

<!--
 Licensed to the Apache Software Foundation (ASF) under one or more
 contributor license agreements.  See the NOTICE file distributed with
 this work for additional information regarding copyright ownership.
 The ASF licenses this file to You under the Apache License, Version 2.0
 (the "License"); you may not use this file except in compliance with
 the License.  You may obtain a copy of the License at

     http://www.apache.org/licenses/LICENSE-2.0

 Unless required by applicable law or agreed to in writing, software
 distributed under the License is distributed on an "AS IS" BASIS,
 WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 See the License for the specific language governing permissions and
 limitations under the License.
-->

<modulesynopsis metafile="mod_authn_socache.xml.meta">

<name>mod_authn_socache</name>
<description>Manages a cache of authentication credentials to relieve
the load on backends</description>
<status>Base</status>
<sourcefile>mod_authn_socache.c</sourcefile>
<identifier>authn_socache_module</identifier>
<compatibility>Version 2.3 and later</compatibility>

<summary>
    <p>Maintains a cache of authentication credentials, so that a new backend
    lookup is not required for every authenticated request.</p>
</summary>

<section id="intro"><title>Authentication Cacheing</title>
    <p>Some users of more heavyweight authentication such as SQL database
    lookups (<module>mod_authn_dbd</module>) have reported it putting an
    unacceptable load on their authentication provider.  A typical case
    in point is where an HTML page contains hundreds of objects
    (images, scripts, stylesheets, media, etc), and a request to the page
    generates hundreds of effectively-immediate requests for authenticated
    additional contents.</p>
    <p>mod_authn_socache provides a solution to this problem by
    maintaining a cache of authentication credentials.</p>
</section>

<section id="usage"><title>Usage</title>
    <p>The authentication cache should be used where authentication
    lookups impose a significant load on the server, or a backend or
    network.  Authentication by file (<module>mod_authn_file</module>)
    or dbm (<module>mod_authn_dbm</module>) are unlikely to benefit,
    as these are fast and lightweight in their own right (though in some
    cases, such as a network-mounted file, cacheing may be worthwhile).
    Other providers such as SQL or LDAP based authentication are more
    likely to benefit, particularly where there is an observed
    performance issue.  Amongst the standard modules, <module
    >mod_authnz_ldap</module> manages its own cache, so only
    <module>mod_authn_dbd</module> will usually benefit from this cache.</p>
    <p>The basic rules to cache for a provider are:</p>
    <ol><li>Include the provider you're cacheing for in an
            <directive>AuthnCacheProvideFor</directive> directive.</li>
        <li>List <var>socache</var> ahead of the provider you're
            cacheing for in your <directive module="mod_auth_basic"
            >AuthBasicProvider</directive> or <directive module=
            "mod_auth_digest">AuthDigestProvider</directive> directive.</li>
    </ol>
    <p>A simple usage example to accelerate <module>mod_authn_dbd</module>
    using dbm as a cache engine:</p>
    <example><pre>
    &lt;Directory /usr/www/myhost/private&gt;
        AuthType Basic
        AuthName "Cached Authentication Example"
        AuthBasicProvider socache dbd
        AuthDBDUserPWQuery "SELECT password FROM authn WHERE user = %s"
        AuthnCacheProvideFor dbd
        AuthnCacheContext dbd-authn-example
        AuthnCacheSOCache dbm
        Require valid-user
    &lt;/Directory&gt;
    </pre></example>
</section>

<section id="dev"><title>Cacheing with custom modules</title>
    <p>Module developers should note that their modules must be enabled
    for cacheing with mod_authn_socache.  A single optional API function
    <var>ap_authn_cache_store</var> is provided to cache credentials
    a provider has just looked up or generated.  Usage examples are
    available in <a
    href="http://svn.eu.apache.org/viewvc?view=revision&amp;revision=957072"
    >r957072</a>, in which three authn providers are enabled for cacheing.</p>
</section>

<directivesynopsis>
<name>AuthnCacheSOCache</name>
<description>Select socache backend provider to use</description>
<syntax>AuthnCacheSOCache <var>provider-name</var></syntax>
<contextlist><context>server config</context></contextlist>
<override>None</override>

<usage>
    <p>This is a server-wide setting to select a provider for the
    <a href="../socache.html">shared object cache</a>.
    Values are "dbm", "dc", "mc", or "shmcb", each subject to the
    appropriate module being loaded.  If not set, your platform's
       default will be used.</p>
</usage>
</directivesynopsis>

<directivesynopsis>
<name>AuthnCacheProvideFor</name>
<description>Specify which authn provider(s) to cache for</description>
<syntax>AuthnCacheProvideFor <var>authn-provider</var> [...]</syntax>
<default>None</default>
<contextlist><context>directory</context><context>.htaccess</context></contextlist>
<override>AuthConfig</override>

<usage>
    <p>This directive specifies an authentication provider or providers
    to cache for.  Credentials found by a provider not listed in an
    AuthnCacheProvideFor directive will not be cached.</p>

    <p>For example, to cache credentials found by <module>mod_authn_dbd</module>
    or by a custom provider <var>myprovider</var>, but leave those looked
    up by lightweight providers like file or dbm lookup alone:</p>
    <example>
        AuthnCacheProvideFor dbd myprovider
    </example>
</usage>
</directivesynopsis>

<directivesynopsis>
<name>AuthnCacheTimeout</name>
<description>Set a timeout for cache entries</description>
<syntax>AuthnCacheTimeout <var>timeout</var> (seconds)</syntax>
<default>300 (5 minutes)</default>
<contextlist><context>directory</context><context>.htaccess</context></contextlist>
<override>AuthConfig</override>

<usage>
    <p>Cacheing authentication data can be a security issue, though short-term
    cacheing is unlikely to be a problem.  Typically a good solution is to
    cache credentials for as long as it takes to relieve the load on a
    backend, but no longer, though if changes to your users and passwords
    are infrequent then a longer timeout may suit you.  The default 300
    seconds (5 minutes) is both cautious and ample to keep the load
    on a backend such as dbd (SQL database queries) down.</p>
    <p>This should not be confused with session timeout, which is an
    entirely separate issue.  However, you may wish to check your
    session-management software for whether cached credentials can
    "accidentally" extend a session, and bear it in mind when setting
    your timeout.</p>
</usage>
</directivesynopsis>

<directivesynopsis>
<name>AuthnCacheContext</name>
<description>Specify a context string for use in the cache key</description>
<syntax>AuthnCacheContext <var>directory|server|custom-string</var></syntax>
<default>directory</default>
<contextlist><context>directory</context></contextlist>

<usage>
    <p>This directive specifies a string to be used along with the supplied
    username (and realm in the case of Digest Authentication) in constructing
    a cache key.  This serves to disambiguate identical usernames serving
    different authentication areas on the server.</p>
    <p>Two special values for this are <var>directory</var>, which uses
    the directory context of the request as a string, and <var>server</var>
    which uses the virtual host name.</p>
    <p>The default is <var>directory</var>, which is also the most
    conservative setting.  This is likely to be less than optimal, as it
    (for example) causes <var>$app-base</var>, <var>$app-base/images</var>,
    <var>$app-base/scripts</var> and <var>$app-base/media</var> each to
    have its own separate cache key.  A better policy is to name the
    <directive>AuthnCacheContext</directive> for the password
    provider: for example a <var>htpasswd</var> file or database table.</p>
    <p>Contexts can be shared across different areas of a server, where
    credentials are shared.  However, this has potential to become a vector
    for cross-site or cross-application security breaches, so this directive
    is not permitted in <var>.htaccess</var> contexts.</p>
</usage>
</directivesynopsis>
 
</modulesynopsis>

