docs/manual/mod/mod_headers.html.en - httpd - Git at Google

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 <p class="apache">Apache HTTP Server Version 2.0</p>
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 <div id="page-content">
 <div class="retired"><h4>Please note</h4>
             <p>This document refers to the <strong>2.0</strong> version of Apache httpd, which <strong>is no longer maintained</strong>. Upgrade, and refer to the current version of httpd instead, documented at:</p>
         <ul><li><a href="http://httpd.apache.org/docs/current/">Current release version of Apache HTTP Server documentation</a></li></ul><p>You may follow <a href="http://httpd.apache.org/docs/current/mod/mod_headers.html">this link</a> to go to the current version of this document.</p></div><div id="preamble"><h1>Apache Module mod_headers</h1>
 <div class="toplang">
 <p><span>Available Languages: </span><a href="../en/mod/mod_headers.html" title="English">&nbsp;en&nbsp;</a> |
 <a href="../ko/mod/mod_headers.html" hreflang="ko" rel="alternate" title="Korean">&nbsp;ko&nbsp;</a></p>
 </div>
 <table class="module"><tr><th><a href="module-dict.html#Description">Description:</a></th><td>Customization of HTTP request and response
 headers</td></tr>
 <tr><th><a href="module-dict.html#Status">Status:</a></th><td>Extension</td></tr>
 <tr><th><a href="module-dict.html#ModuleIdentifier">Module&#160;Identifier:</a></th><td>headers_module</td></tr>
 <tr><th><a href="module-dict.html#SourceFile">Source&#160;File:</a></th><td>mod_headers.c</td></tr></table>
 <h3>Summary</h3>

     <p>This module provides directives to control and modify HTTP
     request and response headers. Headers can be merged, replaced
     or removed.</p>
 </div>
 <div id="quickview"><h3 class="directives">Directives</h3>
 <ul id="toc">
 <li><img alt="" src="../images/down.gif" /> <a href="#header">Header</a></li>
 <li><img alt="" src="../images/down.gif" /> <a href="#requestheader">RequestHeader</a></li>
 </ul>
 <h3>Topics</h3>
 <ul id="topics">
 <li><img alt="" src="../images/down.gif" /> <a href="#order">Order of Processing</a></li>
 <li><img alt="" src="../images/down.gif" /> <a href="#examples">Examples</a></li>
 </ul></div>
 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
 <div class="section">
 <h2><a name="order" id="order">Order of Processing</a></h2>

     <p>The directives provided by <code class="module"><a href="../mod/mod_headers.html">mod_headers</a></code> can occur
     almost anywhere within the server configuration. They are valid in the
     main server config and virtual host sections, inside
     <code class="directive"><a href="../mod/core.html#directory">&lt;Directory&gt;</a></code>,
     <code class="directive"><a href="../mod/core.html#location">&lt;Location&gt;</a></code> and
     <code class="directive"><a href="../mod/core.html#files">&lt;Files&gt;</a></code> sections,
     and within <code>.htaccess</code> files.</p>

     <p>The directives are processed in the following order:</p>

     <ol>
       <li>main server</li>
       <li>virtual host</li>
       <li><code class="directive">&lt;Directory&gt;</code> sections and
       <code>.htaccess</code></li>
       <li><code class="directive">&lt;Files&gt;</code></li>
       <li><code class="directive">&lt;Location&gt;</code></li>
     </ol>

     <p>Order is important. These two headers have a different
     effect if reversed:</p>

     <div class="example"><p><code>
       RequestHeader append MirrorID "mirror 12"<br />
       RequestHeader unset MirrorID
     </code></p></div>

     <p>This way round, the <code>MirrorID</code> header is not set. If
     reversed, the MirrorID header is set to "mirror 12".</p>
 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
 <div class="section">
 <h2><a name="examples" id="examples">Examples</a></h2>

     <ol>
       <li>
         Copy all request headers that begin with "TS" to the
         response headers:

         <div class="example"><p><code>
           Header echo ^TS
         </code></p></div>
       </li>

       <li>
         Add a header, <code>MyHeader</code>, to the response including a
         timestamp for when the request was received and how long it
         took to begin serving the request. This header can be used by
         the client to intuit load on the server or in isolating
         bottlenecks between the client and the server.

         <div class="example"><p><code>
           Header add MyHeader "%D %t"
         </code></p></div>

         <p>results in this header being added to the response:</p>

         <div class="example"><p><code>
           MyHeader: D=3775428 t=991424704447256
         </code></p></div>
       </li>

       <li>
         Say hello to Joe

         <div class="example"><p><code>
           Header add MyHeader "Hello Joe. It took %D microseconds \<br />
           for Apache to serve this request."
         </code></p></div>

         <p>results in this header being added to the response:</p>

         <div class="example"><p><code>
           MyHeader: Hello Joe. It took D=3775428 microseconds for Apache
           to serve this request.
         </code></p></div>
       </li>

       <li>
         Conditionally send <code>MyHeader</code> on the response if and
         only if header "MyRequestHeader" is present on the request. This
         is useful for constructing headers in response to some client
         stimulus. Note that this example requires the services of the
         <code class="module"><a href="../mod/mod_setenvif.html">mod_setenvif</a></code> module.

         <div class="example"><p><code>
           SetEnvIf MyRequestHeader value HAVE_MyRequestHeader<br />
           Header add MyHeader "%D %t mytext" env=HAVE_MyRequestHeader<br />
        </code></p></div>

        <p>If the header <code>MyRequestHeader: value</code> is present on
        the HTTP request, the response will contain the following header:</p>

        <div class="example"><p><code>
          MyHeader: D=3775428 t=991424704447256 mytext
        </code></p></div>
       </li>
     </ol>
 </div>
 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
 <div class="directive-section"><h2><a name="Header" id="Header">Header</a> <a name="header" id="header">Directive</a></h2>
 <table class="directive">
 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Configure HTTP response headers</td></tr>
 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>Header [<var>condition</var>] set|append|add|unset|echo
 <var>header</var> [<var>value</var>] [env=[!]<var>variable</var>]</code></td></tr>
 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host, directory, .htaccess</td></tr>
 <tr><th><a href="directive-dict.html#Override">Override:</a></th><td>FileInfo</td></tr>
 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_headers</td></tr>
 <tr><th><a href="directive-dict.html#Compatibility">Compatibility:</a></th><td><var>Condition</var> is available in version 2.0.51 and
 later</td></tr>
 </table>
     <p>This directive can replace, merge or remove HTTP response
     headers. The header is modified just after the content handler
     and output filters are run, allowing outgoing headers to be
     modified.</p>

     <p>The optional <var>condition</var> can be either <code>onsuccess</code>
     or <code>always</code>. It determines, which internal header table should be
     operated on. <code>onsuccess</code> stands for <code>2<var>xx</var></code>
     status codes and <code>always</code> for all status codes (including
     <code>2<var>xx</var></code>). Especially if you want to unset headers
     set by certain modules, you should try out, which table is affected.</p>

     <p>The action it performs is determined by the second
     argument. This can be one of the following values:</p>

     <dl>
     <dt><code>set</code></dt>
     <dd>The response header is set, replacing any previous header
     with this name. The <var>value</var> may be a format string.</dd>

     <dt><code>append</code></dt>
     <dd>The response header is appended to any existing header of
     the same name. When a new value is merged onto an existing
     header it is separated from the existing header with a comma.
     This is the HTTP standard way of giving a header multiple values.</dd>

     <dt><code>add</code></dt>
     <dd>The response header is added to the existing set of headers,
     even if this header already exists. This can result in two
     (or more) headers having the same name. This can lead to
     unforeseen consequences, and in general "append" should be
     used instead.</dd>

     <dt><code>unset</code></dt>
     <dd>The response header of this name is removed, if it exists.
     If there are multiple headers of the same name, all will be
     removed.</dd>

     <dt><code>echo</code></dt>
     <dd>Request headers with this name are echoed back in the
     response headers. <var>header</var> may be a regular expression.</dd>
     </dl>

     <p>This argument is followed by a <var>header</var> name, which
     can include the final colon, but it is not required. Case is
     ignored for <code>set</code>, <code>append</code>, <code>add</code>
     and <code>unset</code>. The <var>header</var> name for <code>echo</code>
     is case sensitive and may be a regular expression.</p>

     <p>For <code>add</code>, <code>append</code> and <code>set</code> a
     <var>value</var> is specified as the third argument. If <var>value</var>
     contains spaces, it should be surrounded by doublequotes.
     <var>value</var> may be a character string, a string containing format
     specifiers or a combination of both. The following format specifiers
     are supported in <var>value</var>:</p>

     <table class="bordered">

     <tr><td><code>%t</code></td>
         <td>The time the request was received in Universal Coordinated Time
         since the epoch (Jan. 1, 1970) measured in microseconds. The value
         is preceded by <code>t=</code>.</td></tr>

     <tr><td><code>%D</code></td>
         <td>The time from when the request was received to the time the
         headers are sent on the wire. This is a measure of the duration
         of the request. The value is preceded by <code>D=</code>.</td></tr>

     <tr><td><code>%{FOOBAR}e</code></td>
         <td>The contents of the <a href="../env.html">environment
         variable</a> <code>FOOBAR</code>.</td></tr>
     </table>

     <p>When the <code class="directive">Header</code> directive is used with the
     <code>add</code>, <code>append</code>, or <code>set</code>
     argument, a fourth argument may be used to specify conditions
     under which the action will be taken. If the <a href="../env.html">environment variable</a> specified in the
     <code>env=...</code> argument exists (or if the environment
     variable does not exist and <code>env=!...</code> is specified)
     then the action specified by the <code class="directive">Header</code> directive
     will take effect. Otherwise, the directive will have no effect
     on the request.</p>

     <p>The <code class="directive">Header</code> directives are processed just
     before the response is sent to the network. These means that it is
     possible to set and/or override most headers, except for those headers
     added by the header filter.</p>

 </div>
 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
 <div class="directive-section"><h2><a name="RequestHeader" id="RequestHeader">RequestHeader</a> <a name="requestheader" id="requestheader">Directive</a></h2>
 <table class="directive">
 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Configure HTTP request headers</td></tr>
 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>RequestHeader set|append|add|unset <var>header</var>
 [<var>value</var> [env=[!]<var>variable</var>]]</code></td></tr>
 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host, directory, .htaccess</td></tr>
 <tr><th><a href="directive-dict.html#Override">Override:</a></th><td>FileInfo</td></tr>
 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_headers</td></tr>
 </table>
     <p>This directive can replace, merge or remove HTTP request
     headers. The header is modified just before the content handler
     is run, allowing incoming headers to be modified. The action it
     performs is determined by the first argument. This can be one
     of the following values:</p>

     <dl>
     <dt><code>set</code></dt>
     <dd>The request header is set, replacing any previous header
     with this name</dd>

     <dt><code>append</code></dt>
     <dd>The request header is appended to any existing header of the
     same name. When a new value is merged onto an existing header
     it is separated from the existing header with a comma. This
     is the HTTP standard way of giving a header multiple
     values.</dd>

     <dt><code>add</code></dt>
     <dd>The request header is added to the existing set of headers,
     even if this header already exists. This can result in two
     (or more) headers having the same name. This can lead to
     unforeseen consequences, and in general <code>append</code> should be
     used instead.</dd>

     <dt><code>unset</code></dt>
     <dd>The request header of this name is removed, if it exists. If
     there are multiple headers of the same name, all will be removed.</dd>
     </dl>

     <p>This argument is followed by a header name, which can
     include the final colon, but it is not required. Case is
     ignored. For <code>add</code>, <code>append</code> and
     <code>set</code> a <var>value</var> is given as the third argument. If
     <var>value</var> contains spaces, it should be surrounded by double
     quotes. For unset, no <var>value</var> should be given.</p>

     <p>When the <code class="directive">RequestHeader</code> directive is used with the
     <code>add</code>, <code>append</code>, or <code>set</code>
     argument, a fourth argument may be used to specify conditions
     under which the action will be taken. If the <a href="../env.html">environment variable</a> specified in the
     <code>env=...</code> argument exists (or if the environment
     variable does not exist and <code>env=!...</code> is specified)
     then the action specified by the <code class="directive">RequestHeader</code> directive
     will take effect. Otherwise, the directive will have no effect
     on the request.</p>

     <p>The <code class="directive">RequestHeader</code> directive is processed
     just before the request is run by its handler in the fixup phase.
     This should allow headers generated by the browser, or by Apache
     input filters to be overridden or modified.</p>

 </div>
 </div>
 <div class="bottomlang">
 <p><span>Available Languages: </span><a href="../en/mod/mod_headers.html" title="English">&nbsp;en&nbsp;</a> |
 <a href="../ko/mod/mod_headers.html" hreflang="ko" rel="alternate" title="Korean">&nbsp;ko&nbsp;</a></p>
 </div><div id="footer">
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	<title>mod_headers - Apache HTTP Server</title>
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	<p class="apache">Apache HTTP Server Version 2.0</p>
	<img alt="" src="../images/feather.gif" /></div>
	<div class="up"><a href="./"><img title="<-" alt="<-" src="../images/left.gif" /></a></div>
	<div id="path">
	<a href="http://www.apache.org/">Apache</a> > <a href="http://httpd.apache.org/">HTTP Server</a> > <a href="http://httpd.apache.org/docs/">Documentation</a> > <a href="../">Version 2.0</a> > <a href="./">Modules</a></div>
	<div id="page-content">
	<div class="retired"><h4>Please note</h4>
	<p>This document refers to the <strong>2.0</strong> version of Apache httpd, which <strong>is no longer maintained</strong>. Upgrade, and refer to the current version of httpd instead, documented at:</p>
	<ul><li><a href="http://httpd.apache.org/docs/current/">Current release version of Apache HTTP Server documentation</a></li></ul><p>You may follow <a href="http://httpd.apache.org/docs/current/mod/mod_headers.html">this link</a> to go to the current version of this document.</p></div><div id="preamble"><h1>Apache Module mod_headers</h1>
	<div class="toplang">
	<p><span>Available Languages: </span><a href="../en/mod/mod_headers.html" title="English"> en </a> \|
	<a href="../ko/mod/mod_headers.html" hreflang="ko" rel="alternate" title="Korean"> ko </a></p>
	</div>
	<table class="module"><tr><th><a href="module-dict.html#Description">Description:</a></th><td>Customization of HTTP request and response
	headers</td></tr>
	<tr><th><a href="module-dict.html#Status">Status:</a></th><td>Extension</td></tr>
	<tr><th><a href="module-dict.html#ModuleIdentifier">Module Identifier:</a></th><td>headers_module</td></tr>
	<tr><th><a href="module-dict.html#SourceFile">Source File:</a></th><td>mod_headers.c</td></tr></table>
	<h3>Summary</h3>

	<p>This module provides directives to control and modify HTTP
	request and response headers. Headers can be merged, replaced
	or removed.</p>
	</div>
	<div id="quickview"><h3 class="directives">Directives</h3>
	<ul id="toc">
	<li><img alt="" src="../images/down.gif" /> <a href="#header">Header</a></li>
	<li><img alt="" src="../images/down.gif" /> <a href="#requestheader">RequestHeader</a></li>
	</ul>
	<h3>Topics</h3>
	<ul id="topics">
	<li><img alt="" src="../images/down.gif" /> <a href="#order">Order of Processing</a></li>
	<li><img alt="" src="../images/down.gif" /> <a href="#examples">Examples</a></li>
	</ul></div>
	<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
	<div class="section">
	<h2><a name="order" id="order">Order of Processing</a></h2>

	<p>The directives provided by <code class="module"><a href="../mod/mod_headers.html">mod_headers</a></code> can occur
	almost anywhere within the server configuration. They are valid in the
	main server config and virtual host sections, inside
	<code class="directive"><a href="../mod/core.html#directory"><Directory></a></code>,
	<code class="directive"><a href="../mod/core.html#location"><Location></a></code> and
	<code class="directive"><a href="../mod/core.html#files"><Files></a></code> sections,
	and within <code>.htaccess</code> files.</p>

	<p>The directives are processed in the following order:</p>

	<ol>
	<li>main server</li>
	<li>virtual host</li>
	<li><code class="directive"><Directory></code> sections and
	<code>.htaccess</code></li>
	<li><code class="directive"><Files></code></li>
	<li><code class="directive"><Location></code></li>
	</ol>

	<p>Order is important. These two headers have a different
	effect if reversed:</p>

	<div class="example"><p><code>
	RequestHeader append MirrorID "mirror 12"<br />
	RequestHeader unset MirrorID
	</code></p></div>

	<p>This way round, the <code>MirrorID</code> header is not set. If
	reversed, the MirrorID header is set to "mirror 12".</p>
	</div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
	<div class="section">
	<h2><a name="examples" id="examples">Examples</a></h2>

	<ol>
	<li>
	Copy all request headers that begin with "TS" to the
	response headers:

	<div class="example"><p><code>
	Header echo ^TS
	</code></p></div>
	</li>

	<li>
	Add a header, <code>MyHeader</code>, to the response including a
	timestamp for when the request was received and how long it
	took to begin serving the request. This header can be used by
	the client to intuit load on the server or in isolating
	bottlenecks between the client and the server.

	<div class="example"><p><code>
	Header add MyHeader "%D %t"
	</code></p></div>

	<p>results in this header being added to the response:</p>

	<div class="example"><p><code>
	MyHeader: D=3775428 t=991424704447256
	</code></p></div>
	</li>

	<li>
	Say hello to Joe

	<div class="example"><p><code>
	Header add MyHeader "Hello Joe. It took %D microseconds \<br />
	for Apache to serve this request."
	</code></p></div>

	<p>results in this header being added to the response:</p>

	<div class="example"><p><code>
	MyHeader: Hello Joe. It took D=3775428 microseconds for Apache
	to serve this request.
	</code></p></div>
	</li>

	<li>
	Conditionally send <code>MyHeader</code> on the response if and
	only if header "MyRequestHeader" is present on the request. This
	is useful for constructing headers in response to some client
	stimulus. Note that this example requires the services of the
	<code class="module"><a href="../mod/mod_setenvif.html">mod_setenvif</a></code> module.

	<div class="example"><p><code>
	SetEnvIf MyRequestHeader value HAVE_MyRequestHeader<br />
	Header add MyHeader "%D %t mytext" env=HAVE_MyRequestHeader<br />
	</code></p></div>

	<p>If the header <code>MyRequestHeader: value</code> is present on
	the HTTP request, the response will contain the following header:</p>

	<div class="example"><p><code>
	MyHeader: D=3775428 t=991424704447256 mytext
	</code></p></div>
	</li>
	</ol>
	</div>
	<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
	<div class="directive-section"><h2><a name="Header" id="Header">Header</a> <a name="header" id="header">Directive</a></h2>
	<table class="directive">
	<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Configure HTTP response headers</td></tr>
	<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>Header [<var>condition</var>] set\|append\|add\|unset\|echo
	<var>header</var> [<var>value</var>] [env=[!]<var>variable</var>]</code></td></tr>
	<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host, directory, .htaccess</td></tr>
	<tr><th><a href="directive-dict.html#Override">Override:</a></th><td>FileInfo</td></tr>
	<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
	<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_headers</td></tr>
	<tr><th><a href="directive-dict.html#Compatibility">Compatibility:</a></th><td><var>Condition</var> is available in version 2.0.51 and
	later</td></tr>
	</table>
	<p>This directive can replace, merge or remove HTTP response
	headers. The header is modified just after the content handler
	and output filters are run, allowing outgoing headers to be
	modified.</p>

	<p>The optional <var>condition</var> can be either <code>onsuccess</code>
	or <code>always</code>. It determines, which internal header table should be
	operated on. <code>onsuccess</code> stands for <code>2<var>xx</var></code>
	status codes and <code>always</code> for all status codes (including
	<code>2<var>xx</var></code>). Especially if you want to unset headers
	set by certain modules, you should try out, which table is affected.</p>

	<p>The action it performs is determined by the second
	argument. This can be one of the following values:</p>

	<dl>
	<dt><code>set</code></dt>
	<dd>The response header is set, replacing any previous header
	with this name. The <var>value</var> may be a format string.</dd>

	<dt><code>append</code></dt>
	<dd>The response header is appended to any existing header of
	the same name. When a new value is merged onto an existing
	header it is separated from the existing header with a comma.
	This is the HTTP standard way of giving a header multiple values.</dd>

	<dt><code>add</code></dt>
	<dd>The response header is added to the existing set of headers,
	even if this header already exists. This can result in two
	(or more) headers having the same name. This can lead to
	unforeseen consequences, and in general "append" should be
	used instead.</dd>

	<dt><code>unset</code></dt>
	<dd>The response header of this name is removed, if it exists.
	If there are multiple headers of the same name, all will be
	removed.</dd>

	<dt><code>echo</code></dt>
	<dd>Request headers with this name are echoed back in the
	response headers. <var>header</var> may be a regular expression.</dd>
	</dl>

	<p>This argument is followed by a <var>header</var> name, which
	can include the final colon, but it is not required. Case is
	ignored for <code>set</code>, <code>append</code>, <code>add</code>
	and <code>unset</code>. The <var>header</var> name for <code>echo</code>
	is case sensitive and may be a regular expression.</p>

	<p>For <code>add</code>, <code>append</code> and <code>set</code> a
	<var>value</var> is specified as the third argument. If <var>value</var>
	contains spaces, it should be surrounded by doublequotes.
	<var>value</var> may be a character string, a string containing format
	specifiers or a combination of both. The following format specifiers
	are supported in <var>value</var>:</p>

	<table class="bordered">

	<tr><td><code>%t</code></td>
	<td>The time the request was received in Universal Coordinated Time
	since the epoch (Jan. 1, 1970) measured in microseconds. The value
	is preceded by <code>t=</code>.</td></tr>

	<tr><td><code>%D</code></td>
	<td>The time from when the request was received to the time the
	headers are sent on the wire. This is a measure of the duration
	of the request. The value is preceded by <code>D=</code>.</td></tr>

	<tr><td><code>%{FOOBAR}e</code></td>
	<td>The contents of the <a href="../env.html">environment
	variable</a> <code>FOOBAR</code>.</td></tr>
	</table>

	<p>When the <code class="directive">Header</code> directive is used with the
	<code>add</code>, <code>append</code>, or <code>set</code>
	argument, a fourth argument may be used to specify conditions
	under which the action will be taken. If the <a href="../env.html">environment variable</a> specified in the
	<code>env=...</code> argument exists (or if the environment
	variable does not exist and <code>env=!...</code> is specified)
	then the action specified by the <code class="directive">Header</code> directive
	will take effect. Otherwise, the directive will have no effect
	on the request.</p>

	<p>The <code class="directive">Header</code> directives are processed just
	before the response is sent to the network. These means that it is
	possible to set and/or override most headers, except for those headers
	added by the header filter.</p>

	</div>
	<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
	<div class="directive-section"><h2><a name="RequestHeader" id="RequestHeader">RequestHeader</a> <a name="requestheader" id="requestheader">Directive</a></h2>
	<table class="directive">
	<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Configure HTTP request headers</td></tr>
	<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>RequestHeader set\|append\|add\|unset <var>header</var>
	[<var>value</var> [env=[!]<var>variable</var>]]</code></td></tr>
	<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host, directory, .htaccess</td></tr>
	<tr><th><a href="directive-dict.html#Override">Override:</a></th><td>FileInfo</td></tr>
	<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
	<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_headers</td></tr>
	</table>
	<p>This directive can replace, merge or remove HTTP request
	headers. The header is modified just before the content handler
	is run, allowing incoming headers to be modified. The action it
	performs is determined by the first argument. This can be one
	of the following values:</p>

	<dl>
	<dt><code>set</code></dt>
	<dd>The request header is set, replacing any previous header
	with this name</dd>

	<dt><code>append</code></dt>
	<dd>The request header is appended to any existing header of the
	same name. When a new value is merged onto an existing header
	it is separated from the existing header with a comma. This
	is the HTTP standard way of giving a header multiple
	values.</dd>

	<dt><code>add</code></dt>
	<dd>The request header is added to the existing set of headers,
	even if this header already exists. This can result in two
	(or more) headers having the same name. This can lead to
	unforeseen consequences, and in general <code>append</code> should be
	used instead.</dd>

	<dt><code>unset</code></dt>
	<dd>The request header of this name is removed, if it exists. If
	there are multiple headers of the same name, all will be removed.</dd>
	</dl>

	<p>This argument is followed by a header name, which can
	include the final colon, but it is not required. Case is
	ignored. For <code>add</code>, <code>append</code> and
	<code>set</code> a <var>value</var> is given as the third argument. If
	<var>value</var> contains spaces, it should be surrounded by double
	quotes. For unset, no <var>value</var> should be given.</p>

	<p>When the <code class="directive">RequestHeader</code> directive is used with the
	<code>add</code>, <code>append</code>, or <code>set</code>
	argument, a fourth argument may be used to specify conditions
	under which the action will be taken. If the <a href="../env.html">environment variable</a> specified in the
	<code>env=...</code> argument exists (or if the environment
	variable does not exist and <code>env=!...</code> is specified)
	then the action specified by the <code class="directive">RequestHeader</code> directive
	will take effect. Otherwise, the directive will have no effect
	on the request.</p>

	<p>The <code class="directive">RequestHeader</code> directive is processed
	just before the request is run by its handler in the fixup phase.
	This should allow headers generated by the browser, or by Apache
	input filters to be overridden or modified.</p>

	</div>
	</div>
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