How-To / Tutorials

# Access Control

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 are mod_authz_core and mod_authz_host. Also discussed in this document is access control using 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 Require provides a variety of different ways to allow or deny access to resources. In conjunction with the RequireAll, RequireAny, and RequireNone directives, these requirements may be combined in arbitrarily complex ways, to enforce whatever your access policy happens to be.

The Allow, Deny, and Order directives, provided by mod_access_compat, are deprecated and will go away in a future version. You should avoid using them, and avoid outdated tutorials recommending their use.

The usage of these directives is:

Require host address Require ip ip.address

In the first form, address is a fully qualified domain name (or a partial domain name); you may provide multiple addresses or domain names, if desired.

In the second form, ip.address is an IP address, a partial IP address, a network/netmask pair, or a network/nnn CIDR specification. Either IPv4 or IPv6 addresses may be used.

See the mod_authz_host documentation for further examples of this syntax.

You can insert `not` to negate a particular requirement. Note, that since a `not` is a negation of a value, it cannot be used by itself to allow or deny a request, as not true does not constitute false. Thus, to deny a visit using a negation, the block must have one element that evaluates as true or false. For example, if you have someone spamming your message board, and you want to keep them out, you could do the following:

<RequireAll> Require all granted Require not ip 10.252.46.165 </RequireAll>

Visitors coming from that address (`10.252.46.165`) 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.

Require not host 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:

Require not ip 192.168.205 Require not host phishers.example.com moreidiots.example Require not host gov

Use of the RequireAll, RequireAny, and RequireNone directives may be used to enforce more complex sets of requirements.

# Access control by arbitrary variables

Using the If, you can allow or deny access based on arbitrary environment variables or request header values. For example, to deny access based on user-agent (the browser type) you might do the following:

<If "%{HTTP_USER_AGENT} == 'BadBot'"> Require all denied </If>

Using the Require `expr` syntax, this could also be written as:

Require expr %{HTTP_USER_AGENT} != 'BadBot'

## Warning:

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.

See the expressions document for a further discussion of what expression syntaxes and variables are available to you.

# 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.

The If directive, added in 2.4, replaces many things that mod_rewrite has traditionally been used to do, and you should probably look there first before resorting to mod_rewrite.

# More information

The expression engine gives you a great deal of power to do a variety of things based on arbitrary server variables, and you should consult that document for more detail.

Also, you should read the mod_authz_core documentation for examples of combining multiple access requirements and specifying how they interact.

See also the Authentication and Authorization howto.