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<?xml version='1.0' encoding='UTF-8' ?>
<!DOCTYPE manualpage SYSTEM "../style/manualpage.dtd">
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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
<ul>
<li><module>mod_authn_alias</module></li>
<li><module>mod_authn_anon</module></li>
<li><module>mod_authn_core</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="mod_authz_core">Require</directive> and
<directive module="mod_authz_core">Reject</directive> directives)
<ul>
<li><module>mod_authnz_ldap</module></li>
<li><module>mod_authz_core</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_owner</module></li>
<li><module>mod_authz_user</module></li>
</ul>
</li>
</ul>
<p>The module <module>mod_authnz_ldap</module> is both an
authentication and authorization provider. The module
<module>mod_authn_alias</module> is not an authentication provider
in itself, but allows other authentication providers to be
configured in a flexible manner.</p>
<p>The modules <module>mod_authn_core</module> and <module>mod_authz_core
</module> should always be loaded. These module provide the core
directives and functionality that is common to all authentication
and authorization providers.</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>
</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>
</section>
<section id="gettingitworking"><title>Getting it working</title>
<p>Here's the basics of password protecting a directory on your
server.</p>
<p>You'll need to create a password file. 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. 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.
On my server, it's located at
<code>/usr/local/apache/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 <Directory
/usr/local/apache/apache/htdocs/secret> section.</p>
<example>
AuthType Basic<br />
AuthName "Restricted Files"<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. 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. Only the most recent
versions of clients are known to 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>
directive registers which provider or providers will be called to handle
the authentication processing.</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 />
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="whatotherneatstuffcanido"><title>What other neat stuff can I
do?</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 te 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 205.252.46.165
</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>
<RequireAll><br />
Reject ip <var>192.101.205</var><br />
Reject host <var>cyberthugs.com</var> <var>moreidiots.com</var><br />
Reject host ke<br />
</RequireAll>
</example>
<p>Using the <directive module="mod_authz_host">Reject</directive> directive
inside of a <directive module="mod_authz_core"><RequireAll></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">
<RequireAll></directive> block to make sure that all of the
<directive module="mod_authz_host">Reject</directive> directives are
satisfied before granting access. The <directive module="mod_authz_core">
<RequireAll></directive> block as well as the
<directive module="mod_authz_core"><RequireOne></directive> block
allow you to apply "AND" and "OR" logic to the authorization processing.
For example the following authorization block would apply the logic:</p>
<p><var>
if ((user == "John") || <br />
((Group == "admin") && (ldap-group <ldap-object> contains auth'ed_user) &&<br />
((ldap-attribute dept == "sales") ||
(file-group contains contains auth'ed_user))))<br />
then<br />
auth_granted<br />
else<br />
auth_denied<br />
</var></p>
<example>
<Directory /www/mydocs><br />
Authname ...<br />
AuthBasicProvider ...<br />
...<br />
Require user John<br />
<RequireAll><br />
Require Group admins<br />
Require ldap-group cn=mygroup,o=foo<br />
<RequireOne><br />
Require ldap-attribute dept="sales"<br />
Require file-group<br />
</RequireOne><br />
</RequireAll><br />
</Directory><br />
</example>
</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.
<module>mod_authn_alias</module> can also help in simplifying certain
authentication configurations.</p>
</section>
</manualpage>
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