Apache Access Control

While most web server content is created to be available to the public, you may want to restrict some or all of a website to specific users or groups. HTTP Auth lets you easily create these restrictions.

This guide provides an overview of both credential-based and rule-based access control tools for Apache.

Before You Begin

1. If you have not already done so, create a Linode account and Compute Instance. See our Getting Started with Linode and Creating a Compute Instance guides.

2. Follow our Setting Up and Securing a Compute Instance guide to update your system and configure your hostname. You may also wish to set the timezone, create a limited user account, and harden SSH access.

   To check your hostname run:

   hostname
   hostname -f
   

   The first command should show your short hostname, and the second should show your fully qualified domain name (FQDN) if you have one assigned.

Apache Access Control

To enable passwords for a directory, insert the following lines into the appropriate <Directory> section of an Apache configuration file. You may also insert authentication information in an .htaccess file or in a virtual host configuration section. The required directives are:

File: Apache Configuration File

1 2 3 4

AuthType Basic AuthUserFile /var/www/example.com/.htpasswd AuthName "Sign In Here To Gain Access To the Site" Require valid-user

• The AuthType directive specifies which authentication method Apache should use when connecting with clients. Basic requires that passwords be sent as clear text over the network. As a result we don’t recommend using this to protect sensitive resources.

• The AuthUserFile specifies the path (in full) to the password file where the passwords are stored. In this example we’re using the path /var/www/example.com/.htpassword. This is one directory above the public_html folder, preventing accidental exposure of the file. By default, all files beginning with .ht are not web-accessible in most default configurations of Apache, but this should not be assumed.

• The AuthName directive contains the message browser uses to inform the user of what resource they’re authenticating to. The value is arbitrary.

• The Require valid-user setting simply tells Apache that any valid user can authenticate.

At this point we need to create a password file.

Generating HTTP AUTH Passwords

To generate passwords, we need the htpasswd tool. For many distributions, this tool may have been installed when you installed Apache itself. Debian and Ubuntu users will have to install the apache2-utils package with the following commands:

sudo apt-get install apache2-utils

To create a new file with a single user, issue the following command:

htpasswd -c /var/www/example.com/.htpasswd username

In this example, we create a new AuthUserFile with the -c option. The file is located at /var/www/example.com/.htpasswd and the user name is username. htpasswd will prompt you to enter a password and then confirm the password. If you have an existing file, omit the -c option.

The -b option allows you to enter the password as the last parameter of the command, as in this example :

htpasswd -b /srv/auth/.htpasswd username 5t1ck6

The AuthUserFile will, when populated look something like this:

File: /var/www/example.com/.htpasswd

1 2 3

hobby:isiA3Q4djD/.Q admin:{SHA}x9VvwHI6dmgk9VTE0A8o6hbCw2s= username:\$apr1\$vVzQJxvX\$6EyHww61nnZr6IdQv0pVx/

Each user is specified on their own line. Each line follows the form [username]:[hash], where the [hash] is a cryptographic hash of the users’ password. This provides one-way encryption and some small measure of additional security.

In the above example, the first hobby user’s password is hashed using the “CRYPT” method, which is the default. This is not considered a secure encryption mechanism. If you specify the -s option in the htpasswd command, the password will be hashed with the SHA algorithm as in the second line of the above example. Finally, if you specify the -m option, htpasswd will use the MD5 hash to store the password. We recommend using either the SHA or the MD5 hash.

Additionally, if you would prefer to organize and maintain the AuthUserFile yourself, you can still use the htpasswd tool to generate the user entries. By specifying the -n option the program will output the appropriate line in the terminal. In the following example, the htpasswd entry is followed by the output of the command:

htpasswd -nbs user2 strongpassword
user2:{SHA}KuhoB50pPgoYXGcce82sUd8244U=

You can now append the user2:{SHA}KuhoB50pPgoYXGcce82sUd8244U= line to your AuthUserFile manually. Once this line is in the password file, the betty user credentials will be able to authenticate the HTTP server.

Access Control Lists with Groups

In the Require directive above we specified the valid-user. This told Apache that any user who could authenticate against one of the users specified in the AuthUserFile could gain access to the site. While you can maintain separate password files for different resources, this is difficult to maintain for deployments with complex authentication needs.

To address this need, Apache allows you to use a single AuthUserFile, containing all users that will need to authenticate to the server. To limit the set of valid credentials to a specific subset of the users listed in the .htpasswd file, we must specify users in the Require directive. Only users specified after the Require user directive will be permitted to access the specified resource. For example:

File: Apache configuration option

1	Require user username admin

Given this directive, the users username and admin will be able to log into the resource. Any subset of users can be specified on the Require line. Apache also provides the ability to organize users into groups, and then permit access to resources based on group membership. The configuration directives for this setup would look like this:

File: Apache configuration file

1 2 3 4

AuthType Basic AuthUserFile /srv/auth/.htpasswd AuthGroupFile /srv/auth/.htgroup Require group Authorized

In this example, we cite the same AuthUserFile, but we add an AuthGroupFile that specifies user groups. The group file contains a list of user groups and the usernames associated with each group. The htgroup file, like the htpasswd file, can be located anywhere on the file system. For clarity’s sake, we recommend that htgroup be in the same directory as the htpasswd file. Here is an example of an htgroup file:

File: /var/www/example.com/.htgroup

1 2	Authorized: username username2 Team: admin hobby

Given this htgroup file, only the users username and username2 will have access to the above listed resource. The syntax of the group file follows a simple [groupname]: [username 1] [username 2] [...]. You can put as many usernames from your AuthUserFile into a group entry as you need for the particular resource.

The Caveats of HTTP Authentication

• The AuthType Basic directive means credentials are sent unencrypted, which makes HTTP AUTH particularly subject to “man-in-the-middle” attacks. As a result, this authentication method shouldn’t be used for protecting sensitive information without first encrypting the traffic over SSL.

• In HTTP AUTH session authentication credentials must be exchanged between the client and the server for every request. While most client software can cache this information so that the user only has to enter the username and password once, the authentication credentials must be passed for every request. This can add additional network overhead.

• When Apache processes an HTTP AUTH request it must parse through the entire htpasswd file. When the file only stores a few passwords the processing time is negligible, but when password files grow, requests can longer to process.

More Information

You may wish to consult the following resources for additional information on this topic. While these are provided in the hope that they will be useful, please note that we cannot vouch for the accuracy or timeliness of externally hosted materials.

• Installation of the Apache web server
• LAMP stack guides
• Authentication and Access Control
• Basic Authentication Module