path: root/docs/manual/mod/mod_auth_digest.xml

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

<name>mod_auth_digest</name>
<description>User authentication using MD5
    Digest Authentication</description>
<status>Extension</status>
<sourcefile>mod_auth_digest.c</sourcefile>
<identifier>auth_digest_module</identifier>

<summary>
    <p>This module implements HTTP Digest Authentication
    (<a href="http://www.faqs.org/rfcs/rfc2617.html">RFC2617</a>), and
    provides an alternative to <module>mod_auth_basic</module> where the
    password is not transmitted as cleartext. However, this does
    <strong>not</strong> lead to a significant security advantage over
    basic authentication. On the other hand, the password storage on the
    server is much less secure with digest authentication than with
    basic authentication. Therefore, using basic auth and encrypting the
    whole connection using <module>mod_ssl</module> is a much better
    alternative.</p>
</summary>

<seealso><directive module="mod_authn_core">AuthName</directive></seealso>
<seealso><directive module="mod_authn_core">AuthType</directive></seealso>
<seealso><directive module="mod_authz_core">Require</directive></seealso>
<seealso><a href="../howto/auth.html">Authentication howto</a></seealso>

<section id="using"><title>Using Digest Authentication</title>

    <p>To use MD5 Digest authentication, simply
    change the normal <code>AuthType Basic</code> and
    <directive module="mod_auth_basic">AuthBasicProvider</directive>
    to <code>AuthType Digest</code> and
    <directive module="mod_auth_digest">AuthDigestProvider</directive>,
    when setting up authentication, then add a
    <directive module="mod_auth_digest"
    >AuthDigestDomain</directive> directive containing at least the root
    URI(s) for this protection space.</p>

    <p>Appropriate user (text) files can be created using the
    <program>htdigest</program> tool.</p>

    <example><title>Example:</title>
    <highlight language="config">
&lt;Location "/private/"&gt;
    AuthType Digest
    AuthName "private area"
    AuthDigestDomain "/private/" "http://mirror.my.dom/private2/"

    AuthDigestProvider file
    AuthUserFile "/web/auth/.digest_pw"
    Require valid-user
&lt;/Location&gt;
      </highlight>
    </example>

    <note><title>Note</title>
    <p>Digest authentication was intended to be more secure than basic
    authentication, but no longer fulfills that design goal. A
    man-in-the-middle attacker can trivially force the browser to downgrade
    to basic authentication. And even a passive eavesdropper can brute-force
    the password using today's graphics hardware, because the hashing
    algorithm used by digest authentication is too fast. Another problem is
    that the storage of the passwords on the server is insecure. The contents
    of a stolen htdigest file can be used directly for digest authentication.
    Therefore using <module>mod_ssl</module> to encrypt the whole connection is
    strongly recommended.</p>
    <p><module>mod_auth_digest</module> only works properly on platforms
      where APR supports shared memory.</p>
    </note>
</section>


<directivesynopsis>
<name>AuthDigestProvider</name>
<description>Sets the authentication provider(s) for this location</description>
<syntax>AuthDigestProvider <var>provider-name</var>
[<var>provider-name</var>] ...</syntax>
<default>AuthDigestProvider file</default>
<contextlist><context>directory</context><context>.htaccess</context>
</contextlist>
<override>AuthConfig</override>

<usage>
    <p>The <directive>AuthDigestProvider</directive> directive sets
    which provider is used to authenticate the users for this location.
    The default <code>file</code> provider is implemented
    by the <module>mod_authn_file</module> module.  Make sure
    that the chosen provider module is present in the server.</p>

    <p>See <module>mod_authn_dbm</module>, <module>mod_authn_file</module>,
    <module>mod_authn_dbd</module> and <module>mod_authn_socache</module>
    for providers.</p>
</usage>
</directivesynopsis>

<directivesynopsis>
<name>AuthDigestQop</name>
<description>Determines the quality-of-protection to use in digest
authentication</description>
<syntax>AuthDigestQop none|auth|auth-int [auth|auth-int]</syntax>
<default>AuthDigestQop auth</default>
<contextlist><context>directory</context><context>.htaccess</context>
</contextlist>
<override>AuthConfig</override>

<usage>
    <p>The <directive>AuthDigestQop</directive> directive determines
    the <dfn>quality-of-protection</dfn> to use. <code>auth</code> will
    only do authentication (username/password); <code>auth-int</code> is
    authentication plus integrity checking (an MD5 hash of the entity
    is also computed and checked); <code>none</code> will cause the module
    to use the old RFC-2069 digest algorithm (which does not include
    integrity checking). Both <code>auth</code> and <code>auth-int</code> may
    be specified, in which the case the browser will choose which of
    these to use. <code>none</code> should only be used if the browser for
    some reason does not like the challenge it receives otherwise.</p>

    <note>
      <code>auth-int</code> is not implemented yet.
    </note>
</usage>
</directivesynopsis>

<directivesynopsis>
<name>AuthDigestNonceLifetime</name>
<description>How long the server nonce is valid</description>
<syntax>AuthDigestNonceLifetime <var>seconds</var></syntax>
<default>AuthDigestNonceLifetime 300</default>
<contextlist><context>directory</context><context>.htaccess</context>
</contextlist>
<override>AuthConfig</override>

<usage>
    <p>The <directive>AuthDigestNonceLifetime</directive> directive
    controls how long the server nonce is valid. When the client
    contacts the server using an expired nonce the server will send
    back a 401 with <code>stale=true</code>. If <var>seconds</var> is
    greater than 0 then it specifies the amount of time for which the
    nonce is valid; this should probably never be set to less than 10
    seconds. If <var>seconds</var> is less than 0 then the nonce never
    expires. <!-- Not implemented yet: If <var>seconds</var> is 0 then
    the nonce may be used exactly once by the client. Note that while
    one-time-nonces provide higher security against replay attacks,
    they also have significant performance implications, as the
    browser cannot pipeline or multiple connections for the
    requests. Because browsers cannot easily detect that
    one-time-nonces are being used, this may lead to browsers trying
    to pipeline requests and receiving 401 responses for all but the
    first request, requiring the browser to resend the requests. Note
    also that the protection against replay attacks only makes sense
    for dynamically generated content and things like POST requests;
    for static content the attacker may already have the complete
    response, so one-time-nonces do not make sense here.  -->
    </p>
</usage>
</directivesynopsis>

<directivesynopsis>
<name>AuthDigestNonceFormat</name>
<description>Determines how the nonce is generated</description>
<syntax>AuthDigestNonceFormat <var>format</var></syntax>
<contextlist><context>directory</context><context>.htaccess</context>
</contextlist>
<override>AuthConfig</override>

<usage>
    <note>Not implemented yet.</note>
    <!-- The AuthDigestNonceFormat directive determines how the nonce is
    generated. -->
</usage>
</directivesynopsis>

<directivesynopsis>
<name>AuthDigestNcCheck</name>
<description>Enables or disables checking of the nonce-count sent by the
server</description>
<syntax>AuthDigestNcCheck On|Off</syntax>
<default>AuthDigestNcCheck Off</default>
<contextlist><context>server config</context></contextlist>

<usage>
    <note>
      Not implemented yet.
    </note>
    <!--
    <p>The AuthDigestNcCheck directive enables or disables the checking of the
    nonce-count sent by the server.</p>

    <p>While recommended from a security standpoint, turning this directive
    On has one important performance implication. To check the nonce-count
    *all* requests (which have an Authorization header, irrespective of
    whether they require digest authentication) must be serialized through
    a critical section. If the server is handling a large number of
    requests which contain the Authorization header then this may noticeably
    impact performance.</p>
     -->
</usage>
</directivesynopsis>

<directivesynopsis>
<name>AuthDigestAlgorithm</name>
<description>Selects the algorithm used to calculate the challenge and
response hashes in digest authentication</description>
<syntax>AuthDigestAlgorithm MD5|MD5-sess</syntax>
<default>AuthDigestAlgorithm MD5</default>
<contextlist><context>directory</context><context>.htaccess</context>
</contextlist>
<override>AuthConfig</override>

<usage>
    <p>The <directive>AuthDigestAlgorithm</directive> directive
    selects the algorithm used to calculate the challenge and response
    hashes.</p>

    <note>
      <code>MD5-sess</code> is not correctly implemented yet.
    </note>
    <!--
    <p>To use <code>MD5-sess</code> you must first code up the
    <code>get_userpw_hash()</code> function in
    <code>mod_auth_digest.c</code>.</p>
    -->
</usage>
</directivesynopsis>

<directivesynopsis>
<name>AuthDigestDomain</name>
<description>URIs that are in the same protection space for digest
authentication</description>
<syntax>AuthDigestDomain <var>URI</var> [<var>URI</var>] ...</syntax>
<contextlist><context>directory</context><context>.htaccess</context>
</contextlist>
<override>AuthConfig</override>

<usage>
    <p>The <directive>AuthDigestDomain</directive> directive allows
    you to specify one or more URIs which are in the same protection
    space (<em>i.e.</em> use the same realm and username/password info).
    The specified URIs are prefixes; the client will assume
    that all URIs "below" these are also protected by the same
    username/password. The URIs may be either absolute URIs (<em>i.e.</em>
    including a scheme, host, port, etc.) or relative URIs.</p>

    <p>This directive <em>should</em> always be specified and
    contain at least the (set of) root URI(s) for this space.
    Omitting to do so will cause the client to send the
    Authorization header for <em>every request</em> sent to this
    server. Apart from increasing the size of the request, it may
    also have a detrimental effect on performance if <directive
    module="mod_auth_digest">AuthDigestNcCheck</directive> is on.</p>

    <p>The URIs specified can also point to different servers, in
    which case clients (which understand this) will then share
    username/password info across multiple servers without
    prompting the user each time. </p>
</usage>
</directivesynopsis>

<directivesynopsis>
<name>AuthDigestShmemSize</name>
<description>The amount of shared memory to allocate for keeping track
of clients</description>
<syntax>AuthDigestShmemSize <var>size</var></syntax>
<default>AuthDigestShmemSize 1000</default>
<contextlist><context>server config</context></contextlist>

<usage>
    <p>The <directive>AuthDigestShmemSize</directive> directive defines
    the amount of shared memory, that will be allocated at the server
    startup for keeping track of clients. Note that the shared memory
    segment cannot be set less than the space that is necessary for
    tracking at least <em>one</em> client. This value is dependent on your
    system. If you want to find out the exact value, you may simply
    set <directive>AuthDigestShmemSize</directive> to the value of
    <code>0</code> and read the error message after trying to start the
    server.</p>

    <p>The <var>size</var> is normally expressed in Bytes, but you
    may follow the number with a <code>K</code> or an <code>M</code> to
    express your value as KBytes or MBytes. For example, the following
    directives are all equivalent:</p>

<highlight language="config">
AuthDigestShmemSize 1048576
AuthDigestShmemSize 1024K
AuthDigestShmemSize 1M
    </highlight>
</usage>
</directivesynopsis>

</modulesynopsis>