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Access Control

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Access control refers to any means of controlling access to any resource. This is separate from authentication and authorization.


Related Modules and Directives

Access control can be done by several different modules. The most important of these is mod_authz_host. Other modules discussed in this document include mod_setenvif and mod_rewrite.


Access control by host

If you wish to restrict access to portions of your site based on the host address of your visitors, this is most easily done using mod_authz_host.

The Allow and Deny directives let you allow and deny access based on the host name, or host address, of the machine requesting a document. The Order directive goes hand-in-hand with these two, and tells Apache in which order to apply the filters.

The usage of these directives is:

Allow from address

where address 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:

Deny from

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.

Deny from host.example.com

And, if you'd like to block access from an entire domain, you can specify just part of an address or domain name:

Deny from 192.168.205
Deny from phishers.example.com moreidiots.example
Deny from ke

Using Order will let you be sure that you are actually restricting things to the group that you want to let in, by combining a Deny and an Allow directive:

Order deny,allow
Deny from all
Allow from dev.example.com

Listing just the Allow 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.


Access control by environment variable

mod_authz_host, in conjunction with mod_setenvif, can be used to restrict access to your website based on the value of arbitrary environment variables. This is done with the Allow from env= and Deny from env= syntax.

SetEnvIf User-Agent BadBot GoAway=1
Order allow,deny
Allow from all
Deny from env=GoAway


Access control by User-Agent is an unreliable technique, since the User-Agent header can be set to anything at all, at the whim of the end user.

In the above example, the environment variable GoAway is set to 1 if the User-Agent matches the string BadBot. Then we deny access for any request when this variable is set. This blocks that particular user agent from the site.

An environment variable test can be negated using the =! syntax:

Allow from env=!GoAway


Access control with mod_rewrite

The [F] RewriteRule flag causes a 403 Forbidden response to be sent. Using this, you can deny access to a resource based on arbitrary criteria.

For example, if you wish to block access to a resource between 8pm and 6am, you can do this using mod_rewrite.

RewriteEngine On
RewriteCond %{TIME_HOUR} >20 [OR]
RewriteCond %{TIME_HOUR} <07
RewriteRule ^/fridge - [F]

This will return a 403 Forbidden response for any request after 8pm or before 7am. This technique can be used for any criteria that you wish to check. You can also redirect, or otherwise rewrite these requests, if that approach is preferred.


More information

You should also read the documentation for mod_auth_basic and mod_authz_host which contain some more information about how this all works. mod_authn_alias can also help in simplifying certain authentication configurations.

See the Authentication and Authorization howto.

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