Apache User Authentication

A guide to setting up user authentication for the Apache web server running on Linux, using the plaintext file method.
Configuring the Server

Now that the password file has been created, the server must be notified that access will be restricted based on the user names and passwords found in this file (/etc/httpd/users). This protection method provides access control to individual files as well as to directories and their subdirectories. The directives to create the protected area can be placed either in a .htaccess file in the directory to be protected, or in a <Directory> section in the access.conf file (located in /etc/httpd/conf).

Restricting Directories Using .htaccess

To restrict a directory from within a .htaccess file, first ensure that the access.conf file allows user authentication to be set up in a .htaccess file. This is controlled by the AuthConfig override. The access.conf file should include AllowOverride AuthConfig to allow the authentication directives to be contained in a .htaccess file. Now, to restrict a directory to any user listed in the password file, create a .htaccess file (inside the directory to be protected) containing the following directives:

AuthName "Confidential"
AuthType Basic
AuthUserFile /etc/httpd/users
require valid-user
.htaccess Contents Description

The AuthName directive specifies a realm name for this protection. Once a user has entered a valid user name and password, any other resources within the realm name can be accessed with the same user name and password. This can be used to create several areas that share the same user name and password.

The AuthType directive tells the server which protocol is to be used for authentication. Another method, Digest, offering higher security features, is also available in the mod_digest module. Using MD5 Digest authentication is quite simple. Set up authentication using AuthType Digest and an AuthDigestFile instead of the normal AuthType Basic and AuthUserFile. Everything else should remain the same.

The AuthUserFile directive tells the server the location of the user file created by htpasswd. Similarly, when using a group file (described in the next section), use the AuthGroupFile directive to tell the server the location of a group's file.

Last, the require directive tells the server which user names from the file are valid for particular access methods. In this example, the argument valid-user tells the server that any user name in the password file can be used. However, we can configure it to allow only specific users. An example of this would be:

require ibrahim julie carla

This directive allows only ibrahim, julie and carla to access the documents after they enter a correct password. If any other user tries to access this directory, even with the correct password, they would be denied. This approach is very useful for two reasons:

  • Different areas of the server can be restricted to different people with the same password file.

  • If a user is allowed to access different areas, he has to remember only a single password.

Using a Group File

In some cases, we want to allow only selected users to access a particular directory. A lazy way of doing this is by listing all the allowed user names on the require line. This is not encouraged since, if there are many users, the file will become quite large. Luckily, there is a nice way around this problem—using a group file which operates in a similar way to standard UNIX groups. Any particular user can be a member of any number of groups. We can then use the require directive line to restrict users to one or more particular groups. For example, we could create a group called research-staff containing users who are allowed to access the research department pages. To restrict access to just users in the research-staff group, we would use this directive:

require group research-staff

Multiple groups can also be listed, and require user can also be given, in which case any user in any of the listed groups, or any user listed explicitly, can access the resource. For example:

require group research-staff admin-staff
require user julia carla
allows any user in group research-staff or group admin-staff, or both users julia and carla, to access this resource after entering a valid password.

A group file consists of lines giving a group name followed by a space-separated list of users in that group. For example:

research-staff:chady karine
admin-staff:ibrahim julie

The AuthGroupFile directive is used to tell the server the location of the group file. The catch with using a group file is that the maximum line length within the group file is 8KB. However, to get around this limit, we can have more than one line with the same group name within the file.