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Extensible Markup Language | 2004-05-23 | 16KB | 361 lines

<?xml version='1.0' encoding='UTF-8' ?> <!DOCTYPE manualpage SYSTEM "../style/manualpage.dtd"> <?xml-stylesheet type="text/xsl" href="../style/manual.en.xsl"?>   <manualpage metafile="auth.xml.meta"> <parentdocument href="./">How-To / Tutorials</parentdocument> <title>Authentication, Authorization and Access Control</title> <summary> 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. </summary> <section id="related"><title>Related Modules and Directives</title> <related> <modulelist> <module>mod_auth</module> <module>mod_access</module> </modulelist> <directivelist> <directive module="mod_access">Allow</directive> <directive module="mod_auth">AuthGroupFile</directive> <directive module="core">AuthName</directive> <directive module="core">AuthType</directive> <directive module="mod_auth">AuthUserFile</directive> <directive module="mod_access">Deny</directive> <directive module="core">Options</directive> <directive module="core">Require</directive> </directivelist> </related> </section> <section id="introduction"><title>Introduction</title> 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. This article covers the "standard" way of protecting parts of your web site that most of you are going to use. </section> <section id="theprerequisites"><title>The Prerequisites</title> 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). 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. Since we're talking here about authentication, you will need an <directive module="core">AllowOverride</directive> directive like the following: <example> AllowOverride AuthConfig </example> 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. 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. </section> <section id="gettingitworking"><title>Getting it working</title> Here's the basics of password protecting a directory on your server. 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>. To create the file, use the <a href="../programs/htpasswd.html">htpasswd</a> 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: <example> htpasswd -c /usr/local/apache/passwd/passwords rbowen </example> <code>htpasswd</code> will ask you for the password, and then ask you to type it again to confirm it: <example> # htpasswd -c /usr/local/apache/passwd/passwords rbowen New password: mypassword Re-type new password: mypassword Adding password for user rbowen </example> If <code>htpasswd</code> 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> 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. <example> AuthType Basic AuthName "Restricted Files" AuthUserFile /usr/local/apache/passwd/passwords Require user rbowen </example> 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</module>. It is important to be aware, however, that Basic authentication sends the password from the client to the browser 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. 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. 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. The <directive module="mod_auth">AuthUserFile</directive> directive sets the path to the password file that we just created with <code>htpasswd</code>. 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_auth_dbm</module> module provides the <directive module="mod_auth_dbm">AuthDBMUserFile</directive> directive. These files can be created and manipulated with the <a href="../programs/dbmmanage.html">dbmmanage</a> 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>. 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. </section> <section id="lettingmorethanonepersonin"><title>Letting more than one person in</title> 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_auth" >AuthGroupFile</directive> comes in. 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: <example> GroupName: rbowen dpitts sungo rshersey </example> That's just a list of the members of the group in a long line separated by spaces. To add a user to your already existing password file, type: <example> htpasswd /usr/local/apache/passwd/passwords dpitts </example> 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). Now, you need to modify your <code>.htaccess</code> file to look like the following: <example> AuthType Basic AuthName "By Invitation Only" AuthUserFile /usr/local/apache/passwd/passwords AuthGroupFile /usr/local/apache/passwd/groups Require group GroupName </example> 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. 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: <example> Require valid-user </example> 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_auth">AuthUserFile</directive> directive. </section> <section id="possibleproblems"><title>Possible problems</title> 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. 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. </section> <section id="whatotherneatstuffcanido"><title>What other neat stuff can I do?</title> 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. The <directive module="mod_access">Allow</directive> and <directive module="mod_access">Deny</directive> directives let you allow and deny access based on the host name, or host address, of the machine requesting a document. The <directive module="mod_access">Order</directive> directive goes hand-in-hand with these two, and tells Apache in which order to apply the filters. The usage of these directives is: <example> Allow from <var>address</var> </example> where <var>address</var> is an IP address (or a partial IP address) or a fully qualified domain name (or a partial domain name); you may provide multiple addresses or domain names, if desired. For example, if you have someone spamming your message board, and you want to keep them out, you could do the following: <example> Deny from 205.252.46.165 </example> 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. <example> Deny from <var>host.example.com</var> </example> And, if you'd like to block access from an entire domain, you can specify just part of an address or domain name: <example> Deny from <var>192.101.205</var> Deny from <var>cyberthugs.com</var> <var>moreidiots.com</var> Deny from ke </example> Using <directive module="mod_access">Order</directive> will let you be sure that you are actually restricting things to the group that you want to let in, by combining a <directive module="mod_access">Deny</directive> and an <directive module="mod_access">Allow</directive> directive: <example> Order deny,allow Deny from all Allow from <var>dev.example.com</var> </example> Listing just the <directive module="mod_access">Allow</directive> directive would not do what you want, because it will let folks from that host in, in addition to letting everyone in. What you want is to let only those folks in. </section> <section id="moreinformation"><title>More information</title> You should also read the documentation for <module>mod_auth</module> and <module>mod_access</module> which contain some more information about how this all works. </section> </manualpage>