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(see PR 63923) git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1869811 13f79535-47bb-0310-9956-ffa450edef68
704 lines
24 KiB
XML
704 lines
24 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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<!-- $LastChangedRevision$ -->
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<!--
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Licensed to the Apache Software Foundation (ASF) under one or more
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contributor license agreements. See the NOTICE file distributed with
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this work for additional information regarding copyright ownership.
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The ASF licenses this file to You under the Apache License, Version 2.0
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(the "License"); you may not use this file except in compliance with
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the License. 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_policy.xml.meta">
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<name>mod_policy</name>
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<description>HTTP protocol compliance enforcement.</description>
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<status>Extension</status>
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<sourcefile>mod_policy.c</sourcefile>
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<identifier>policy_module</identifier>
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<summary>
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<p>The HTTP protocol recommends that clients should be "liberal in
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what they accept", and servers "strict with what they send". In some
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cases it can be difficult to detect when a server or an application
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has been misconfigured, is serving uncacheable content or is behaving
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suboptimally, as an HTTP client might be compensating for the server.
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These problems can potentially lead to excessive bandwidth
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consumption, or a server outage under load.</p>
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<p>The <module>mod_policy</module> module consists of a set of
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filters that test servers for HTTP protocol compliance. These
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tests allow the server administrator to log violations of, or
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outright reject responses where certain defined conditions exist.</p>
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<p>This could be used as a way to set minimum HTTP protocol compliance
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criteria for a restful application. Alternatively, a reverse proxy or
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cache could be configured to protect itself from misconfigured origin
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servers or unexpectedly uncacheable content, or as a mechanism to
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detect configuration mistakes within the server itself.</p>
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</summary>
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<seealso><a href="../filter.html">Filters</a></seealso>
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<seealso><a href="../compliance.html">HTTP Protocol Compliance</a></seealso>
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<section id="actions">
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<title>Actions</title>
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<p>If a policy is violated, one of the following actions can be
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taken:</p>
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<dl>
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<dt><strong>ignore</strong></dt>
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<dd>The policy check will be ignored for the given URL space, even
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if the filter is present.</dd>
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<dt><strong>log</strong></dt>
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<dd>The policy check will be executed, and if a violation is detected
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a warning will be logged to the server error_log, and a
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<code>Warning</code> header added to the response for the benefit of
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the client.</dd>
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<dt><strong>enforce</strong></dt>
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<dd>The policy check will be executed, and if a violation is detected
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an error will be logged to the server error_log, a
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<code>Warning</code> header added to the response, and a <code>502
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Bad Gateway</code> will be returned to the client. Optional links to
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explanatory documentation can be added to each error message,
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detailing the origin of each policy.</dd>
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</dl>
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<p>It is also possible to selectively disable all policies for a
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given URL space, should the need arise, using the
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<directive module="mod_policy">PolicyFilter</directive> directive.</p>
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<p>Alternatively, the
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<directive module="mod_policy">PolicyEnvironment</directive>
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directive can be used to specify an environment variable, which if
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present, will cause the policies to be selectively downgraded or
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bypassed.</p>
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</section>
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<section id="tests">
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<title>Policy Tests</title>
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<p>The following policy filters are available:</p>
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<dl>
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<dt><strong><a href="../compliance.html#policytype">POLICY_TYPE</a>
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</strong>: Enforce valid content types</dt>
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<dd>Content types that are syntactically invalid or blank can be detected
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and the request rejected. Types can be restricted to a specific list
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containing optional wildcards ? and *.</dd>
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<dt><strong><a href="../compliance.html#policylength">POLICY_LENGTH</a>
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</strong>: Enforce the presence of a Content-Length</dt>
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<dd>The length of responses can be specified in one of three ways, by
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specifying an explicit length in advance, using chunked encoding to set
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the length, or by setting no length at all and terminating the request
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when complete. The absence of a specific content length can affect the
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cacheability of the response, and prevents the use of keepalive during
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HTTP/1.0 requests. This policy enforces the presence of an explicit
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content length on the response.</dd>
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<dt><strong><a href="../compliance.html#policykeepalive">POLICY_KEEPALIVE
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</a></strong>: Enforce the option to keepalive</dt>
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<dd>Less restrictive than the POLICY_LENGTH test, this policy enforces the
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possibility that the response can be kept alive. If the response doesn't
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have a protocol defined zero length, and the response isn't already an
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error, and the response has neither a Content-Length or is declared
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HTTP/1.1 and lacks Content-Encoding: chunked, then this response will be
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rejected.</dd>
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<dt><strong><a href="../compliance.html#policyvary">POLICY_VARY</a>
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</strong>: Enforce the absence of certain headers within Vary headers</dt>
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<dd>If the Vary header contains any of the headers specified, this policy
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will reject the request. The typical case is the presence of the User-Agent
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within Vary, which is likely to cause a denial of service condition to a
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cache.</dd>
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<dt><strong><a href="../compliance.html#policyvalidation">
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POLICY_VALIDATION</a></strong>: Enforce the presence of Etag and/or
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Last-Modified</dt>
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<dd>The ability for a cache to determine whether a cached entity can be
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refreshed is dependent on whether a valid Etag and/or Last-Modified header
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is present to revalidate against. The absence of both headers, or the
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invalid syntax of a header will cause this policy to be rejected.</dd>
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<dt><strong><a href="../compliance.html#policyconditional">
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POLICY_CONDITIONAL</a></strong>: Enforce correct operation of conditional
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requests</dt>
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<dd>When conditional headers are present in the request, a server should
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respond with a <code>304 Not Modified</code> or <code>412 Precondition
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Failed</code> response where appropriate. A server may ignore conditional
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headers, and this affects the efficiency of the HTTP caching mechanism.
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This policy rejects requests where a conditional header is present, and
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a 304 or 412 response code was expected, but a 2xx response was seen
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instead.</dd>
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<dt><strong><a href="../compliance.html#policynocache">POLICY_NOCACHE</a>
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</strong>: Enforce cacheable responses</dt>
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<dd>When a response is encountered that declares itself explicitly
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uncacheable, the request is rejected. A response is considered
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uncacheable if it specifies any of the following:
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<ul><li><code>Cache-Control: no-cache</code></li>
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<li><code>Pragma: no-cache</code></li>
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<li><code>Cache-Control: no-store</code></li>
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<li><code>Cache-Control: private</code></li>
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</ul></dd>
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<dt><strong><a href="../compliance.html#policymaxage">POLICY_MAXAGE</a>
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</strong>: Enforce a minimum maxage</dt>
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<dd>When a response is encountered where the freshness lifetime is less
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than the given value, or the freshness lifetime is heuristic, the request
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is rejected. A response is checked in the following order:
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<ul><li>If <code>s-maxage</code> is present but too small; or</li>
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<li>If <code>max-age</code> is present but too small; or</li>
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<li>If <code>Expires</code> is present and invalid; or</li>
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<li><code>Date</code> is present and invalid; or</li>
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<li><code>Expires</code> minus Date is too small; or</li>
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<li>No <code>s-maxage</code>, <code>maxage</code>, or
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<code>Expires</code>/<code>Date</code> declared at all</li>
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</ul></dd>
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<dt><strong><a href="../compliance.html#policyversion">POLICY_VERSION</a>
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</strong>: Enforce a minimum HTTP version within a request</dt>
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<dd>When a request is encountered with an HTTP version number less than
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the required minimum version, the request is rejected. The following
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version numbers are recognised:
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<ul><li><code>HTTP/1.1</code></li>
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<li><code>HTTP/1.0</code></li>
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<li><code>HTTP/0.9</code></li>
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</ul></dd>
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</dl>
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</section>
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<section id="example">
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<title>Example Configuration</title>
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<p>A typical configuration protecting a server serving static content
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might be as follows:</p>
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<highlight language="config">
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<Location "/">
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SetOutputFilter POLICY_TYPE;POLICY_LENGTH;POLICY_KEEPALIVE;POLICY_VARY;POLICY_VALIDATION; \
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POLICY_CONDITIONAL;POLICY_NOCACHE;POLICY_MAXAGE;POLICY_VERSION
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# content type must be present and valid, but can be anything
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PolicyType enforce */*
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# reject if no explicitly declared content length
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PolicyLength enforce
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# covered by the policy length filter
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PolicyKeepalive ignore
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# reject if User-Agent appears within Vary headers
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PolicyVary enforce User-Agent
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# we want to enforce validation
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PolicyValidation enforce
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# non-functional conditional responses should be rejected
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PolicyConditional enforce
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# no-cache responses should be rejected
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PolicyNocache enforce
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# maxage must be at least a day
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PolicyMaxage enforce 86400
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# request version can be anything
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PolicyVersion ignore HTTP/1.1
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</Location>
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# suppress policy protection for server-status
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<Location "/server-status">
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PolicyFilter off
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</Location>
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</highlight>
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</section>
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<directivesynopsis>
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<name>PolicyFilter</name>
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<description>Enable or disable policies for the given URL space.</description>
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<syntax>PolicyFilter <var>on|off</var></syntax>
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<default>on</default>
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<contextlist><context>server config</context><context>virtual host</context>
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<context>directory</context></contextlist>
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<compatibility>PolicyFilter is only available in Apache 2.5.0 and
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later.</compatibility>
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<usage>
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<p>Master switch to enable or disable policies for a given URL space.</p>
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<example><title>Example</title>
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<highlight language="config">
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# enabled by default
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<Location "/">
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PolicyFilter on
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</Location>
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# suppress policy protection for server-status
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<Location "/server-status">
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PolicyFilter off
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</Location>
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</highlight>
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</example>
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</usage>
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</directivesynopsis>
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<directivesynopsis>
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<name>PolicyEnvironment</name>
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<description>Override policies based on an environment variable.</description>
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<syntax>PolicyEnvironment <var>variable</var> <var>log-value</var> <var>ignore-value</var></syntax>
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<default>none</default>
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<contextlist><context>server config</context><context>virtual host</context>
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<context>directory</context></contextlist>
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<compatibility>PolicyEnvironment is only available in Apache 2.5.0 and
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later.</compatibility>
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<usage>
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<p>Downgrade policies to logging only or ignored based on the presence
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of an environment variable. If the given variable is present and equal
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to the log-value, enforced policies will be logged instead. If the given
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variable is present and equal to the ignore-value, all policies will
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be ignored.</p>
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<example><title>Example</title>
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<highlight language="config">
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# downgrade if POLICY_CONTROL was present
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PolicyEnvironment POLICY_CONTROL log ignore
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</highlight>
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</example>
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</usage>
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</directivesynopsis>
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<directivesynopsis>
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<name>PolicyConditional</name>
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<description>Enable the conditional request policy.</description>
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<syntax>PolicyConditional <var>ignore|log|enforce</var></syntax>
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<default>ignore</default>
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<contextlist><context>server config</context><context>virtual host</context>
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<context>directory</context></contextlist>
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<compatibility>PolicyConditional is only available in Apache 2.5.0 and
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later.</compatibility>
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<usage>
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<p>When logged or enforced, a response that should have been conditional
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but wasn't will be rejected.</p>
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<example><title>Example</title>
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<highlight language="config">
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# non-functional conditional responses should be rejected
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PolicyConditional enforce
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</highlight>
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</example>
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</usage>
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</directivesynopsis>
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<directivesynopsis>
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<name>PolicyConditionalURL</name>
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<description>URL describing the conditional request policy.</description>
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<syntax>PolicyConditionalURL <var>url</var></syntax>
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<default>none</default>
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<contextlist><context>server config</context><context>virtual host</context>
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<context>directory</context></contextlist>
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<compatibility>PolicyConditionalURL is only available in Apache 2.5.0 and
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later.</compatibility>
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<usage>
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<p>Specify the URL of the documentation describing the conditional
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request policy, to appear within error messages.</p>
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</usage>
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</directivesynopsis>
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<directivesynopsis>
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<name>PolicyLength</name>
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<description>Enable the content length policy.</description>
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<syntax>PolicyLength <var>ignore|log|enforce</var></syntax>
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<default>ignore</default>
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<contextlist><context>server config</context><context>virtual host</context>
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<context>directory</context></contextlist>
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<compatibility>PolicyLength is only available in Apache 2.5.0 and
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later.</compatibility>
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<usage>
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<p>When logged or enforced, a response that lacks an explicit
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<code>Content-Length</code> header will be rejected.</p>
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<example><title>Example</title>
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<highlight language="config">
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# missing Content-Length header should be rejected
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PolicyLength enforce
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</highlight>
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</example>
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</usage>
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</directivesynopsis>
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<directivesynopsis>
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<name>PolicyLengthURL</name>
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<description>URL describing the content length policy.</description>
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<syntax>PolicyLengthURL <var>url</var></syntax>
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<default>none</default>
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<contextlist><context>server config</context><context>virtual host</context>
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<context>directory</context></contextlist>
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<compatibility>PolicyLengthURL is only available in Apache 2.5.0 and
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later.</compatibility>
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<usage>
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<p>Specify the URL of the documentation describing the content length
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policy, to appear within error messages.</p>
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</usage>
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</directivesynopsis>
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<directivesynopsis>
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<name>PolicyKeepalive</name>
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<description>Enable the keepalive policy.</description>
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<syntax>PolicyKeepalive <var>ignore|log|enforce</var></syntax>
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<default>ignore</default>
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<contextlist><context>server config</context><context>virtual host</context>
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<context>directory</context></contextlist>
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<compatibility>PolicyKeepalive is only available in Apache 2.5.0 and
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later.</compatibility>
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<usage>
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<p>When logged or enforced, a response that lacks both an explicit
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<code>Content-Length</code> header and a <code>Transfer-Encoding</code>
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of <code>chunked</code> will be rejected.</p>
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<example><title>Example</title>
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<highlight language="config">
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# missing Content-Length or Transfer-Encoding should be rejected
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PolicyKeepalive enforce
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</highlight>
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</example>
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</usage>
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</directivesynopsis>
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<directivesynopsis>
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<name>PolicyKeepaliveURL</name>
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<description>URL describing the keepalive policy.</description>
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<syntax>PolicyKeepaliveURL <var>url</var></syntax>
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<default>none</default>
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<contextlist><context>server config</context><context>virtual host</context>
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<context>directory</context></contextlist>
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<compatibility>PolicyKeepaliveURL is only available in Apache 2.5.0 and
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later.</compatibility>
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<usage>
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<p>Specify the URL of the documentation describing the keepalive
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policy, to appear within error messages.</p>
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</usage>
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</directivesynopsis>
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<directivesynopsis>
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<name>PolicyType</name>
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<description>Enable the content type policy.</description>
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<syntax>PolicyType <var>ignore|log|enforce</var> <var>type</var> [ <var>type</var> [ ... ]]</syntax>
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<default>ignore</default>
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<contextlist><context>server config</context><context>virtual host</context>
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<context>directory</context></contextlist>
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<compatibility>PolicyType is only available in Apache 2.5.0 and
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later.</compatibility>
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<usage>
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<p>When logged or enforced, a response that lacks a <code>Content-Type</code>
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header, where the <code>Content-Type</code> header is malformed, or where the
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header does not match the given pattern or patterns will be rejected.</p>
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<example><title>Example</title>
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<highlight language="config">
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# enforce json or XML
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PolicyType enforce application/json text/xml
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</highlight>
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</example>
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<example><title>Example</title>
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<highlight language="config">
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# malformed content type should be rejected
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PolicyType enforce */*
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</highlight>
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</example>
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</usage>
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</directivesynopsis>
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<directivesynopsis>
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<name>PolicyTypeURL</name>
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<description>URL describing the content type policy.</description>
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<syntax>PolicyTypeURL <var>url</var></syntax>
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<default>none</default>
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<contextlist><context>server config</context><context>virtual host</context>
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<context>directory</context></contextlist>
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<compatibility>PolicyTypeURL is only available in Apache 2.5.0 and
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later.</compatibility>
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<usage>
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<p>Specify the URL of the documentation describing the content type
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policy, to appear within error messages.</p>
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</usage>
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</directivesynopsis>
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<directivesynopsis>
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<name>PolicyVary</name>
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<description>Enable the Vary policy.</description>
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<syntax>PolicyVary <var>ignore|log|enforce</var> <var>header</var> [ <var>header</var> [ ... ]]</syntax>
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<default>ignore</default>
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<contextlist><context>server config</context><context>virtual host</context>
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<context>directory</context></contextlist>
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<compatibility>PolicyVary is only available in Apache 2.5.0 and
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later.</compatibility>
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<usage>
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<p>When logged or enforced, a response that contains a <code>Vary</code>
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header which in turn contains one of the headers listed, will be
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rejected.</p>
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<example><title>Example</title>
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<highlight language="config">
|
|
# reject responses with "User-Agent" listed in the Vary header
|
|
PolicyVary enforce User-Agent
|
|
</highlight>
|
|
</example>
|
|
|
|
</usage>
|
|
|
|
</directivesynopsis>
|
|
|
|
<directivesynopsis>
|
|
|
|
<name>PolicyVaryURL</name>
|
|
<description>URL describing the content type policy.</description>
|
|
<syntax>PolicyVaryURL <var>url</var></syntax>
|
|
<default>none</default>
|
|
<contextlist><context>server config</context><context>virtual host</context>
|
|
<context>directory</context></contextlist>
|
|
<compatibility>PolicyVaryURL is only available in Apache 2.5.0 and
|
|
later.</compatibility>
|
|
|
|
<usage>
|
|
<p>Specify the URL of the documentation describing the vary policy, to
|
|
appear within error messages.</p>
|
|
</usage>
|
|
|
|
</directivesynopsis>
|
|
|
|
<directivesynopsis>
|
|
|
|
<name>PolicyValidation</name>
|
|
<description>Enable the validation policy.</description>
|
|
<syntax>PolicyValidation <var>ignore|log|enforce</var></syntax>
|
|
<default>ignore</default>
|
|
<contextlist><context>server config</context><context>virtual host</context>
|
|
<context>directory</context></contextlist>
|
|
<compatibility>PolicyValidation is only available in Apache 2.5.0 and
|
|
later.</compatibility>
|
|
|
|
<usage>
|
|
<p>When logged or enforced, a response that lacks either a valid
|
|
<code>ETag</code> header or a <code>Last-Modified</code> header, or where
|
|
either header is syntactically incorrect, will be rejected.</p>
|
|
|
|
<example><title>Example</title>
|
|
<highlight language="config">
|
|
# no ETag or Last-Modified will be rejected
|
|
PolicyValidation enforce
|
|
</highlight>
|
|
</example>
|
|
|
|
</usage>
|
|
|
|
</directivesynopsis>
|
|
|
|
<directivesynopsis>
|
|
|
|
<name>PolicyValidationURL</name>
|
|
<description>URL describing the content type policy.</description>
|
|
<syntax>PolicyValidationURL <var>url</var></syntax>
|
|
<default>none</default>
|
|
<contextlist><context>server config</context><context>virtual host</context>
|
|
<context>directory</context></contextlist>
|
|
<compatibility>PolicyValidationURL is only available in Apache 2.5.0 and
|
|
later.</compatibility>
|
|
|
|
<usage>
|
|
<p>Specify the URL of the documentation describing the validation policy, to
|
|
appear within error messages.</p>
|
|
</usage>
|
|
|
|
</directivesynopsis>
|
|
|
|
<directivesynopsis>
|
|
|
|
<name>PolicyNocache</name>
|
|
<description>Enable the caching no-cache policy.</description>
|
|
<syntax>PolicyNocache <var>ignore|log|enforce</var></syntax>
|
|
<default>ignore</default>
|
|
<contextlist><context>server config</context><context>virtual host</context>
|
|
<context>directory</context></contextlist>
|
|
<compatibility>PolicyNocache is only available in Apache 2.5.0 and
|
|
later.</compatibility>
|
|
|
|
<usage>
|
|
<p>When logged or enforced, a response that defines itself uncacheable
|
|
using the <code>Cache-Control</code> or <code>Pragma</code> headers will
|
|
be rejected.</p>
|
|
|
|
<example><title>Example</title>
|
|
<highlight language="config">
|
|
# Cache-Control: no-cache will be rejected
|
|
PolicyNocache enforce
|
|
</highlight>
|
|
</example>
|
|
|
|
</usage>
|
|
|
|
</directivesynopsis>
|
|
|
|
<directivesynopsis>
|
|
|
|
<name>PolicyNocacheURL</name>
|
|
<description>URL describing the caching no-cache policy.</description>
|
|
<syntax>PolicyNocacheURL <var>url</var></syntax>
|
|
<default>none</default>
|
|
<contextlist><context>server config</context><context>virtual host</context>
|
|
<context>directory</context></contextlist>
|
|
<compatibility>PolicyNocacheURL is only available in Apache 2.5.0 and
|
|
later.</compatibility>
|
|
|
|
<usage>
|
|
<p>Specify the URL of the documentation describing the caching no-cache
|
|
policy, to appear within error messages.</p>
|
|
</usage>
|
|
|
|
</directivesynopsis>
|
|
|
|
<directivesynopsis>
|
|
|
|
<name>PolicyMaxage</name>
|
|
<description>Enable the caching minimum max-age policy.</description>
|
|
<syntax>PolicyMaxage <var>ignore|log|enforce</var> <var>age</var></syntax>
|
|
<default>ignore</default>
|
|
<contextlist><context>server config</context><context>virtual host</context>
|
|
<context>directory</context></contextlist>
|
|
<compatibility>PolicyMaxage is only available in Apache 2.5.0 and
|
|
later.</compatibility>
|
|
|
|
<usage>
|
|
<p>When logged or enforced, a response that lacks an explicit freshness
|
|
lifetime defined with <code>max-age</code>, <code>s-maxage</code> or an
|
|
<code>Expires</code> header, or where the explicit freshness lifetime is
|
|
smaller than the given value, will be rejected.</p>
|
|
|
|
<example><title>Example</title>
|
|
<highlight language="config">
|
|
# reject responses with a freshness lifetime shorter than a day
|
|
PolicyMaxage enforce 86400
|
|
</highlight>
|
|
</example>
|
|
|
|
</usage>
|
|
|
|
</directivesynopsis>
|
|
|
|
<directivesynopsis>
|
|
|
|
<name>PolicyMaxageURL</name>
|
|
<description>URL describing the caching minimum freshness lifetime policy.</description>
|
|
<syntax>PolicyMaxageURL <var>url</var></syntax>
|
|
<default>none</default>
|
|
<contextlist><context>server config</context><context>virtual host</context>
|
|
<context>directory</context></contextlist>
|
|
<compatibility>PolicyMaxageURL is only available in Apache 2.5.0 and
|
|
later.</compatibility>
|
|
|
|
<usage>
|
|
<p>Specify the URL of the documentation describing the caching minimum
|
|
freshness lifetime policy, to appear within error messages.</p>
|
|
</usage>
|
|
|
|
</directivesynopsis>
|
|
|
|
<directivesynopsis>
|
|
|
|
<name>PolicyVersion</name>
|
|
<description>Enable the version policy.</description>
|
|
<syntax>PolicyVersion <var>ignore|log|enforce</var> <var>HTTP/0.9|HTTP/1.0|HTTP/1.1</var></syntax>
|
|
<default>ignore</default>
|
|
<contextlist><context>server config</context><context>virtual host</context>
|
|
<context>directory</context></contextlist>
|
|
<compatibility>PolicyVersion is only available in Apache 2.5.0 and
|
|
later.</compatibility>
|
|
|
|
<usage>
|
|
<p>When logged or enforced, a request with a version lower than specified
|
|
will be rejected.</p>
|
|
|
|
<example><title>Example</title>
|
|
<highlight language="config">
|
|
# reject requests with an HTTP version older than HTTP/1.1
|
|
PolicyVersion enforce HTTP/1.1
|
|
</highlight>
|
|
</example>
|
|
|
|
</usage>
|
|
|
|
</directivesynopsis>
|
|
|
|
<directivesynopsis>
|
|
|
|
<name>PolicyVersionURL</name>
|
|
<description>URL describing the minimum request HTTP version policy.</description>
|
|
<syntax>PolicyVersionURL <var>url</var></syntax>
|
|
<default>none</default>
|
|
<contextlist><context>server config</context><context>virtual host</context>
|
|
<context>directory</context></contextlist>
|
|
<compatibility>PolicyVersionURL is only available in Apache 2.5.0 and
|
|
later.</compatibility>
|
|
|
|
<usage>
|
|
<p>Specify the URL of the documentation describing the minimum request
|
|
HTTP version policy, to appear within error messages.</p>
|
|
</usage>
|
|
|
|
</directivesynopsis>
|
|
|
|
</modulesynopsis>
|