doc-en/features/http-auth.xml

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 <chapter xml:id="features.http-auth" xmlns="http://docbook.org/ns/docbook" xmlns:xlink="http://www.w3.org/1999/xlink">
  <title>HTTP authentication with PHP</title>

  <simpara>
   It is possible to use the 
   <function>header</function> function to send an <literal>"Authentication Required"</literal> 
   message to the client browser causing it to pop up a Username/Password 
   input window.  Once the user has filled in a username and a password, 
   the URL containing the PHP script will be called again with the 
   <link linkend="reserved.variables">predefined variables</link> 
   <varname>PHP_AUTH_USER</varname>, <varname>PHP_AUTH_PW</varname>, 
   and <varname>AUTH_TYPE</varname> set to the user name, password and 
   authentication type respectively.  These predefined variables are found 
   in the <varname>$_SERVER</varname> array. <emphasis>Only</emphasis>
   the "Basic" authentication method is supported. See the
   <function>header</function> function for more information.
  </simpara>

  <para>
   An example script fragment which would force client authentication
   on a page is as follows:
  </para>
  <para>
   <example>
    <title>Basic HTTP Authentication example</title>
    <programlisting role="php">
<![CDATA[
<?php
if (!isset($_SERVER['PHP_AUTH_USER'])) {
    header('WWW-Authenticate: Basic realm="My Realm"');
    header('HTTP/1.0 401 Unauthorized');
    echo 'Text to send if user hits Cancel button';
    exit;
} else {
    echo "<p>Hello {$_SERVER['PHP_AUTH_USER']}.</p>";
    echo "<p>You entered {$_SERVER['PHP_AUTH_PW']} as your password.</p>";
}
?>
]]>
    </programlisting>
   </example>
  </para>

  <note>
   <title>Compatibility Note</title>
   <para>
    Please be careful when coding the HTTP header lines. In order to guarantee maximum
    compatibility with all clients, the keyword "Basic" should be written with an
    uppercase "B", the realm string must be enclosed in double (not single) quotes,
    and exactly one space should precede the <emphasis>401</emphasis> code in the 
    <emphasis>HTTP/1.0 401</emphasis> header line. Authentication parameters have
    to be comma-separated as seen in the digest example above.
   </para>
  </note>

  <para>
   Instead of simply printing out <varname>PHP_AUTH_USER</varname> 
   and <varname>PHP_AUTH_PW</varname>, as done in the above example, 
   you may want to check the username and password for validity.  
   Perhaps by sending a query to a database, or by looking up the 
   user in a dbm file.
  </para>

  <para>
   Watch out for buggy Internet Explorer browsers out there.  They
   seem very picky about the order of the headers.  Sending the
   <emphasis>WWW-Authenticate</emphasis> header before the
   <literal>HTTP/1.0 401</literal> header seems to do the trick
   for now.
  </para>

  <note>
   <title>Configuration Note</title>
   <para>
    PHP uses the presence of an <literal>AuthType</literal> directive
    to determine whether external authentication is in effect.
   </para>
  </note>

  <simpara>
   Note, however, that the above does not prevent someone who
   controls a non-authenticated URL from stealing passwords from
   authenticated URLs on the same server.
  </simpara>
  <simpara>
   Both Netscape Navigator and Internet Explorer will clear the local browser
   window's authentication cache for the realm upon receiving a
   server response of 401. This can effectively "log out" a user,
   forcing them to re-enter their username and password. Some people
   use this to "time out" logins, or provide a "log-out" button.
  </simpara>
  <para>
   <example>
    <title>HTTP Authentication example forcing a new name/password</title>
    <programlisting role="php">
<![CDATA[
<?php
function authenticate() {
    header('WWW-Authenticate: Basic realm="Test Authentication System"');
    header('HTTP/1.0 401 Unauthorized');
    echo "You must enter a valid login ID and password to access this resource\n";
    exit;
}
 
if (!isset($_SERVER['PHP_AUTH_USER']) ||
    ($_POST['SeenBefore'] == 1 && $_POST['OldAuth'] == $_SERVER['PHP_AUTH_USER'])) {
    authenticate();
} else {
    echo "<p>Welcome: " . htmlspecialchars($_SERVER['PHP_AUTH_USER']) . "<br />";
    echo "Old: " . htmlspecialchars($_REQUEST['OldAuth']);
    echo "<form action='' method='post'>\n";
    echo "<input type='hidden' name='SeenBefore' value='1' />\n";
    echo "<input type='hidden' name='OldAuth' value=\"" . htmlspecialchars($_SERVER['PHP_AUTH_USER']) . "\" />\n";
    echo "<input type='submit' value='Re Authenticate' />\n";
    echo "</form></p>\n";
}
?>
]]>
    </programlisting>
   </example>
  </para>
  <simpara>
   This behavior is not required by the <literal>HTTP Basic</literal>
   authentication standard, so you should never depend on this. Testing with
   <literal>Lynx</literal> has shown that <literal>Lynx</literal> does not clear
   the authentication credentials with a 401 server response, so pressing back
   and then forward again will open the resource as long as the credential
   requirements haven't changed. The user can press the
   <literal>'_'</literal> key to clear their authentication information, however.
  </simpara>
  <simpara>
   In order to get HTTP Authentication to work using IIS server with the CGI version
   of PHP you must edit your IIS configuration "<literal>Directory Security</literal>".
   Click on "<literal>Edit</literal>" and only check
   "<literal>Anonymous Access</literal>", all other fields
   should be left unchecked.
  </simpara>
  <note>
   <title>IIS Note:</title>
   <simpara>
    For HTTP Authentication to work with IIS, the PHP directive
    <link linkend="ini.cgi.rfc2616-headers">cgi.rfc2616_headers</link> must
    be set to <literal>0</literal> (the default value).
   </simpara>
  </note>

 </chapter>

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