apache/docs/manual/howto/auth.xml

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<manualpage metafile="auth.xml.meta">
<parentdocument href="./">How-To / Tutorials</parentdocument>

<title>Authentication, Authorization and Access Control</title>

<summary>
    <p>Authentication is any process by which you verify that
    someone is who they claim they are. Authorization is any
    process by which someone is allowed to be where they want to
    go, or to have information that they want to have.</p>
</summary>

<section id="related"><title>Related Modules and Directives</title>

<p>There are three types of modules involved in the authentication and
authorization process.  You will usually need to choose at least one
module from each group.</p>

<ul>
  <li>Authentication type (see the 
      <directive module="core">AuthType</directive> directive)
    <ul>
      <li><module>mod_auth_basic</module></li>
      <li><module>mod_auth_digest</module></li>
    </ul>
  </li>
  <li>Authentication provider (see the 
  <directive module="mod_auth_basic">AuthBasicProvider</directive> and
  <directive module="mod_auth_digest">AuthDigestProvider</directive> directives)

    <ul>
      <li><module>mod_authn_anon</module></li>
      <li><module>mod_authn_dbd</module></li>
      <li><module>mod_authn_dbm</module></li>
      <li><module>mod_authn_default</module></li>
      <li><module>mod_authn_file</module></li>
      <li><module>mod_authnz_ldap</module></li>
    </ul>
  </li>
  <li>Authorization (see the 
      <directive module="core">Require</directive> directive)
    <ul>
      <li><module>mod_authnz_ldap</module></li>
      <li><module>mod_authz_dbm</module></li>
      <li><module>mod_authz_dbm</module></li>
      <li><module>mod_authz_default</module></li>
      <li><module>mod_authz_groupfile</module></li>
      <li><module>mod_authz_host</module></li>
      <li><module>mod_authz_owner</module></li>
      <li><module>mod_authz_user</module></li>
    </ul>
  </li>
</ul>

  <p>In addition to these modules, there are also 
  <module>mod_authn_core</module> and 
  <module>mod_authz_core</module>.  These module implement core
  directives that are core to all auth modules.</p>

  <p>The module <module>mod_authnz_ldap</module> is both an
  authentication and authorization provider.  The module 
  <module>mod_authz_host</module> provides authorization
  and access control based on hostname, IP address or characteristics
  of the request, but is not part of the authentication provider
  system. For backwards compatibility with the mod_access, there is 
  a new module <module>mod_access_compat</module>.</p>

  <p>You probably also want to take a look at the <a
  href="access.html">Access Control</a> howto, which discusses the
  various ways to control access to your server.</p>

</section>

<section id="introduction"><title>Introduction</title>
    <p>If you have information on your web site that is sensitive
    or intended for only a small group of people, the techniques in
    this article will help you make sure that the people that see
    those pages are the people that you wanted to see them.</p>

    <p>This article covers the "standard" way of protecting parts
    of your web site that most of you are going to use.</p>

    <note><title>Note:</title>
    <p>If your data really needs to be secure, consider using
    <module>mod_ssl</module> in addition to any authentication.</p>
    </note>
</section>

<section id="theprerequisites"><title>The Prerequisites</title>
    <p>The directives discussed in this article will need to go
    either in your main server configuration file (typically in a
    <directive module="core" type="section">Directory</directive> section), or
    in per-directory configuration files (<code>.htaccess</code> files).</p>

    <p>If you plan to use <code>.htaccess</code> files, you will
    need to have a server configuration that permits putting
    authentication directives in these files. This is done with the
    <directive module="core">AllowOverride</directive> directive, which
    specifies which directives, if any, may be put in per-directory
    configuration files.</p>

    <p>Since we're talking here about authentication, you will need
    an <directive module="core">AllowOverride</directive> directive like the
    following:</p>

    <example>
      AllowOverride AuthConfig
    </example>

    <p>Or, if you are just going to put the directives directly in
    your main server configuration file, you will of course need to
    have write permission to that file.</p>

    <p>And you'll need to know a little bit about the directory
    structure of your server, in order to know where some files are
    kept. This should not be terribly difficult, and I'll try to
    make this clear when we come to that point.</p>

    <p>You will also need to make sure that the modules 
    <module>mod_authn_core</module> and <module>mod_authz_core</module> 
    have either been built into the httpd binary or loaded by the 
    httpd.conf configuration file. Both of these modules provide core 
    directives and functionality that are critical to the configuration 
    and use of authentication and authorization in the web server.</p>
</section>

<section id="gettingitworking"><title>Getting it working</title>
    <p>Here's the basics of password protecting a directory on your
    server.</p>

    <p>First, you need to create a password file. Exactly how you do
    this will vary depending on what authentication provider you have
    chosen. More on that later. To start with, we'll use a text password
    file.</p>

    <p>This file should be
    placed somewhere not accessible from the web. This is so that
    folks cannot download the password file. For example, if your
    documents are served out of <code>/usr/local/apache/htdocs</code> you
    might want to put the password file(s) in
    <code>/usr/local/apache/passwd</code>.</p>

    <p>To create the file, use the <program>htpasswd</program> utility that
    came with Apache. This will be located in the <code>bin</code> directory
    of wherever you installed Apache. If you have installed Apache from
    a third-party package, it may be in your execution path.</p>
    
    <p>To create the file, type:</p>

    <example>
      htpasswd -c /usr/local/apache/passwd/passwords rbowen
    </example>

    <p><program>htpasswd</program> will ask you for the password, and
    then ask you to type it again to confirm it:</p>

    <example>
      # htpasswd -c /usr/local/apache/passwd/passwords rbowen<br />
      New password: mypassword<br />
      Re-type new password: mypassword<br />
      Adding password for user rbowen
    </example>

    <p>If <program>htpasswd</program> is not in your path, of course
    you'll have to type the full path to the file to get it to run.
    With a default installation, it's located at
    <code>/usr/local/apache2/bin/htpasswd</code></p>

    <p>Next, you'll need to configure the server to request a
    password and tell the server which users are allowed access.
    You can do this either by editing the <code>httpd.conf</code>
    file or using an <code>.htaccess</code> file. For example, if
    you wish to protect the directory
    <code>/usr/local/apache/htdocs/secret</code>, you can use the
    following directives, either placed in the file
    <code>/usr/local/apache/htdocs/secret/.htaccess</code>, or
    placed in <code>httpd.conf</code> inside a &lt;Directory
    /usr/local/apache/htdocs/secret&gt; section.</p>

    <example>
      AuthType Basic<br />
      AuthName "Restricted Files"<br />
      # (Following line optional)<br />
      AuthBasicProvider file<br />
      AuthUserFile /usr/local/apache/passwd/passwords<br />
      Require user rbowen
    </example>

    <p>Let's examine each of those directives individually. The <directive
    module="core">AuthType</directive> directive selects
    that method that is used to authenticate the user. The most
    common method is <code>Basic</code>, and this is the method
    implemented by <module>mod_auth_basic</module>. It is important to be aware,
    however, that Basic authentication sends the password from the client to
    the server unencrypted. This method should therefore not be used for
    highly sensitive data, unless accompanied by <module>mod_ssl</module>.
    Apache supports one other authentication method:
    <code>AuthType Digest</code>. This method is implemented by <module
    >mod_auth_digest</module> and is much more secure. Most recent
    browsers support Digest authentication.</p>

    <p>The <directive module="core">AuthName</directive> directive sets
    the <dfn>Realm</dfn> to be used in the authentication. The realm serves
    two major functions. First, the client often presents this information to
    the user as part of the password dialog box. Second, it is used by the
    client to determine what password to send for a given authenticated
    area.</p>

    <p>So, for example, once a client has authenticated in the
    <code>"Restricted Files"</code> area, it will automatically
    retry the same password for any area on the same server that is
    marked with the <code>"Restricted Files"</code> Realm.
    Therefore, you can prevent a user from being prompted more than
    once for a password by letting multiple restricted areas share
    the same realm. Of course, for security reasons, the client
    will always need to ask again for the password whenever the
    hostname of the server changes.</p>

    <p>The <directive
    module="mod_auth_basic">AuthBasicProvider</directive> is,
    in this case, optional, since <code>file</code> is the default value
    for this directive. You'll need to use this directive if you are
    choosing a different source for authentication, such as
    <module>mod_authn_dbm</module> or <module>mod_authn_dbd</module>.</p>

    <p>The <directive module="mod_authn_file">AuthUserFile</directive>
    directive sets the path to the password file that we just
    created with <program>htpasswd</program>. If you have a large number
    of users, it can be quite slow to search through a plain text
    file to authenticate the user on each request. Apache also has
    the ability to store user information in fast database files.
    The <module>mod_authn_dbm</module> module provides the <directive
    module="mod_authn_dbm">AuthDBMUserFile</directive> directive. These
    files can be created and manipulated with the <program>
    dbmmanage</program> program. Many
    other types of authentication options are available from third
    party modules in the <a
    href="http://modules.apache.org/">Apache Modules
    Database</a>.</p>

    <p>Finally, the <directive module="core">Require</directive>
    directive provides the authorization part of the process by
    setting the user that is allowed to access this region of the
    server. In the next section, we discuss various ways to use the
    <directive module="core">Require</directive> directive.</p>
</section>

<section id="lettingmorethanonepersonin"><title>Letting more than one
person in</title>
    <p>The directives above only let one person (specifically
    someone with a username of <code>rbowen</code>) into the
    directory. In most cases, you'll want to let more than one
    person in. This is where the <directive module="mod_authz_groupfile"
    >AuthGroupFile</directive> comes in.</p>

    <p>If you want to let more than one person in, you'll need to
    create a group file that associates group names with a list of
    users in that group. The format of this file is pretty simple,
    and you can create it with your favorite editor. The contents
    of the file will look like this:</p>

   <example>
     GroupName: rbowen dpitts sungo rshersey
   </example>

    <p>That's just a list of the members of the group in a long
    line separated by spaces.</p>

    <p>To add a user to your already existing password file,
    type:</p>

    <example>
      htpasswd /usr/local/apache/passwd/passwords dpitts
    </example>

    <p>You'll get the same response as before, but it will be
    appended to the existing file, rather than creating a new file.
    (It's the <code>-c</code> that makes it create a new password
    file).</p>

    <p>Now, you need to modify your <code>.htaccess</code> file to
    look like the following:</p>

    <example>
      AuthType Basic<br />
      AuthName "By Invitation Only"<br />
      # Optional line:<br />
      AuthBasicProvider file<br />
      AuthUserFile /usr/local/apache/passwd/passwords<br />
      AuthGroupFile /usr/local/apache/passwd/groups<br />
      Require group GroupName
    </example>

    <p>Now, anyone that is listed in the group <code>GroupName</code>,
    and has an entry in the <code>password</code> file, will be let in, if
    they type the correct password.</p>

    <p>There's another way to let multiple users in that is less
    specific. Rather than creating a group file, you can just use
    the following directive:</p>

    <example>
      Require valid-user
    </example>

    <p>Using that rather than the <code>Require user rbowen</code>
    line will allow anyone in that is listed in the password file,
    and who correctly enters their password. You can even emulate
    the group behavior here, by just keeping a separate password
    file for each group. The advantage of this approach is that
    Apache only has to check one file, rather than two. The
    disadvantage is that you have to maintain a bunch of password
    files, and remember to reference the right one in the
    <directive module="mod_authn_file">AuthUserFile</directive> directive.</p>
</section>

<section id="possibleproblems"><title>Possible problems</title>
    <p>Because of the way that Basic authentication is specified,
    your username and password must be verified every time you
    request a document from the server. This is even if you're
    reloading the same page, and for every image on the page (if
    they come from a protected directory). As you can imagine, this
    slows things down a little. The amount that it slows things
    down is proportional to the size of the password file, because
    it has to open up that file, and go down the list of users
    until it gets to your name. And it has to do this every time a
    page is loaded.</p>

    <p>A consequence of this is that there's a practical limit to
    how many users you can put in one password file. This limit
    will vary depending on the performance of your particular
    server machine, but you can expect to see slowdowns once you
    get above a few hundred entries, and may wish to consider a
    different authentication method at that time.</p>
</section>

<section id="dbmdbd"><title>Alternate password storage</title>

    <p>Because storing passwords in plain text files has the above
    problems, you may wish to store your passwords somewhere else, such
    as in a database.</p>

    <p><module>mod_authn_dbm</module> and <module>mod_authn_dbd</module>
    are two modules which make this possible. Rather than selecting
    <directive module="mod_auth_basic">AuthBasicSource</directive> file,
    instead you can choose <code>dbm</code> or <code>dbd</code> as your
    storage format.</p>

    <p>To select a dbd file rather than a text file, for example:</p>

    <example>
    &lt;Directory /www/docs/private&gt;<br />
    AuthName "Private"<br />
    AuthType Basic<br />
    AuthBasicProvider dbm<br />
    AuthDBMUserFile /www/passwords/passwd.dbm<br />
    Require valid-user<br />
    &lt;/Directory&gt;
    </example>

    <p>Other options are available. Consult the
    <module>mod_authn_dbm</module> documentation for more details.</p>
</section>

<section id="multprovider"><title>Using multiple providers</title>

    <p>With the introduction of the new provider based authentication and
    authorization architecture, you are no longer locked into a single 
    authentication or authorization method. In fact any number of the 
    providers can be mixed and matched to provide you with exactly the 
    scheme that meets your needs. In the following example, both the 
    file and ldap based authentication providers are being used.</p>

    <example>
    &lt;Directory /www/docs/private&gt;<br />
    AuthName "Private"<br />
    AuthType Basic<br />
    AuthBasicProvider file ldap<br />
    AuthUserFile /usr/local/apache/passwd/passwords<br />
    AuthLDAPURL ldap://ldaphost/o=yourorg<br />
    Require valid-user
    </example>

    <p>In this example the file provider will attempt to authenticate
    the user first. If it is unable to authenticate the user, the ldap
    provider will be called. This allows the scope of authentication
    to be broadened if your organization implements more than
    one type of authentication store. Other authentication and authorization
    scenarios may include mixing one type of authentication with a
    different type of authorization. For example, authenticating against
    a password file yet authorizing against and ldap directory.</p>

    <p>Just as multiple authentication providers can be implemented, multiple
    authorization methods can also be used. In this example both file group
    authorization as well as ldap group authorization is being used.</p>

    <example>
    &lt;Directory /www/docs/private&gt;<br />
    AuthName "Private"<br />
    AuthType Basic<br />
    AuthBasicProvider file<br />
    AuthUserFile /usr/local/apache/passwd/passwords<br />
    AuthLDAPURL ldap://ldaphost/o=yourorg
    AuthGroupFile /usr/local/apache/passwd/groups<br />
    Require group GroupName<br />
    Require ldap-group cn=mygroup,o=yourorg
    </example>

    <p>To take authorization a little further, the directives
    <directive module="mod_authz_core">&lt;SatisfyAll&gt;</directive> and
    <directive module="mod_authz_core">&lt;SatisfyOne&gt;</directive> allow
    AND/OR logic to be applied so that the order in which authorization
    is handled can be completely controled through the configuration. See
    these directives for a complete example on they can be applied.</p>

</section>

<section id="beyond"><title>Beyond just authorization</title>

    <p>The way that authorization can be apply is now much more flexible 
    than just a single check against a single data store. Ordering, logic
    and choosing how authorization will be done is now possible.</p>

    <section id="authandororder"><title>Applying AND/OR logic and ordering</title>
        <p>Controling how and in what order authorization will be applied
        has been a bit of a mystery in the past. In Apache 2.2 a provider based
        authentication mechanism was introduced to decouple the actual 
        authentication process from authorization and supporting functionality.
        One of the side benefits was that authentication providers could be
        configured and called in a specific order which didn't depend on the 
        load order of the auth module itself. This same provider based mechanism 
        has been brought forward into authorization as well. What this means is 
        that the <directive module="mod_authz_core">Require</directive> directive 
        not only specifies which authorization methods should be used, it also 
        specifies the order in which they are called. Multiple authorization 
        methods are called in the same order in which the 
        <directive module="mod_authz_core">Require</directive> directives appear 
        in the configuration.</p>

        <p>With the introduction of the directives 
        <directive module="mod_authz_core">&lt;SatisfyAll&gt;</directive> and 
        <directive module="mod_authz_core">&lt;SatisfyOne&gt;</directive>, the 
        configuration also has control over when the
        authorization methods are called and what criteria determines when 
        access is granted. For example the following authorization block would 
        apply the logic:</p>

        <example>
          # if ((user == "John") ||<br />
          # &nbsp;&nbsp; ((Group == "admin")<br />
          # &nbsp; &nbsp; &amp;&amp; (ldap-group &lt;ldap-object&gt; contains auth'ed_user)<br />
          # &nbsp; &nbsp; &amp;&amp; ((ldap-attribute dept == "sales")<br />
          # &nbsp; &nbsp; &nbsp; &nbsp; || (file-group contains auth'ed_user))))<br />
          # then<br />
          # &nbsp; auth_granted<br />
          # else<br />
          # &nbsp; auth_denied<br />
          #<br />
          &lt;Directory /www/mydocs&gt;<br />
          <indent>
            Authname ...<br />
            AuthBasicProvider ...<br />
            ...<br />
            Require user John<br />
            &lt;SatisfyAll&gt;<br />
            <indent>
              Require Group admins<br />
              Require ldap-group cn=mygroup,o=foo<br />
              &lt;SatisfyOne&gt;<br />
              <indent>
                Require ldap-attribute dept="sales"<br />
                Require file-group<br />
              </indent>
              &lt;/SatisfyOne&gt;<br />
            </indent>
            &lt;/SatisfyAll&gt;<br />
          </indent>
          &lt;/Directory&gt;
        </example>

        <p>By default all <directive module="mod_authz_core">Require</directive> 
        directives are handled through and OR operation. In other words, if 
        any of the specified authorization methods succeed, then authorization 
        is granted. By enclosing a set of 
        <directive module="mod_authz_core">Require</directive> directives within
        a <directive module="mod_authz_core">&lt;SatisfyAll&gt;</directive> block,
        the processing switches to an AND operation which requires all authorization 
        methods to succeed before authorization is granted.</p>

    </section>

    <section id="reqaccessctrl"><title>Using 'Require' or 'Reject' for access control</title>
        <p>Authentication by username and password is only part of the
        story. Frequently you want to let people in based on something
        other than who they are. Something such as where they are
        coming from.</p>
    
        <p>The authorization providers <directive module="mod_authz_host">
        all</directive>, <directive module="mod_authz_host">
        env</directive>, <directive module="mod_authz_host">
        host</directive> and <directive module="mod_authz_host">
        ip</directive> let you allow or deny access based other host based
        criteria such as host name or ip address of the machine requesting 
        a document.</p> 
    
        <p>The usage of these providers is specified through the 
        <directive module="mod_authz_core">Require</directive> and 
        <directive module="mod_authz_core">Reject</directive> directives.
        These directives register the authorization providers
        that will be called during the authorization stage of the request
        processing. For example:</p>
    
        <example>
          Require ip <var>address</var>
        </example>
    
        <p>where <var>address</var> is an IP address (or a partial IP
        address) or:</p>
    
        <example>
          Require host <var>domain_name</var>
        </example>
    
        <p>where <var>domain_name</var> is a fully qualified domain name 
        (or a partial domain name); you may provide multiple addresses or 
        domain names, if desired.</p>
    
        <p>For example, if you have someone spamming your message
        board, and you want to keep them out, you could do the
        following:</p>
    
        <example>
          Reject ip 10.252.46.165
        </example>
    
        <p>Visitors coming from that address will not be able to see
        the content covered by this directive. If, instead, you have a
        machine name, rather than an IP address, you can use that.</p>
    
        <example>
          Reject host <var>host.example.com</var>
        </example>
    
        <p>And, if you'd like to block access from an entire domain,
        you can specify just part of an address or domain name:</p>
    
        <example>
          &lt;SatisfyAll&gt;<br />
          <indent>
            Reject ip <var>192.168.205</var><br />
            Reject host <var>phishers.example.com</var> <var>moreidiots.example</var><br />           Reject host ke<br />
          </indent>
          &lt;/SatisfyAll&gt;
        </example>
    
        <p>Using the <directive module="mod_authz_host">Reject</directive> directive
        inside of a <directive module="mod_authz_core">&lt;SatisfyAll&gt;</directive>
        block, will let you be sure that you are actually restricting things to 
        only the group that you want to let in.</p>
    
        <p>The above example uses the <directive module="mod_authz_core">
        &lt;SatisfyAll&gt;</directive> block to make sure that all of the 
        <directive module="mod_authz_host">Reject</directive> directives are 
        satisfied before granting access. </p>
    
    </section>

    <section id="filesystem"><title>Access Control backwards compatibility</title>
        <p>One of the side effects of adopting a provider based mechanism for 
        authentication is that the need for the previous access control directives
        <directive module="mod_access_compat">Order</directive>,
        <directive module="mod_access_compat">Allow</directive>,
        <directive module="mod_access_compat">Deny</directive> and 
        <directive module="mod_access_compat">Satisfy</directive> are no longer needed. 
        However to provide backwards compatibility for older configurations, these 
        directives have been moved to the <module>mod_access_compat</module> module.</p>

        <p>One of the problems with these directives was that the line between
        authorization and access control was very fuzzy. The 
        <directive module="mod_access_compat">Satisfy</directive> directive
        tried to tie these two stages together by hooking itself into the 
        request processing itself. Now that these directive have been moved to the
        <module>mod_access_compat</module>, mixing the new authorization directives
        with the older access control directives becomes difficult. To address this
        issue, the <module>mod_authz_default</module> module becomes very important and must
        be loaded. The main purpose of the <module>mod_authz_default</module> module is 
        to handle any authorization requests that could not be handled by the 
        authorization providers. But when the older access control directives are used, 
        it also links access control with authorization and determines if access 
        should be granted based on the outcome of each stage. Therefore if the 
        older directives do not seem to be working properly, it might be because the
        <module>mod_authz_default</module> module has not been loaded.</p>

    </section>

</section>

<section id="moreinformation"><title>More information</title>
    <p>You should also read the documentation for
    <module>mod_auth_basic</module> and <module>mod_authz_host</module> which
    contain some more information about how this all works.
    The directive <directive module="mod_authn_core">&lt;AuthnProviderAlias&gt;</directive> 
    can also help in simplifying certain authentication configurations.</p>

    <p>And you may want to look at the <a href="access.html">Access
    Control</a> howto, which discusses a number of related topics.</p>

</section>

</manualpage>