Apache module mod_access

### Apache HTTP Server Version 1.3

# Module mod_access

This module provides access control based on client hostname, IP address, or other characteristics of the client request.

Status: Base
Source File: mod_access.c
Module Identifier: access_module

## Summary

The directives provided by mod_access are used in `<Directory>, <Files>,` and `<Location>` sections as well as `.htaccess` files to control access to particular parts of the server. Access can be controlled based on the client hostname, IP address, or other characteristics of the client request, as captured in environment variables. The `Allow` and `Deny` directives are used to specify which clients are or are not allowed access to the server, while the `Order` directive sets the default access state, and configures how the `Allow` and `Deny` directives interact with each other.

Both host-based access restrictions and password-based authentication may be implemented simultaneously. In that case, the Satisfy directive is used to determine how the two sets of restrictions interact.

In general, access restriction directives apply to all access methods (`GET`, `PUT`, `POST`, etc). This is the desired behavior in most cases. However, it is possible to restrict some methods, while leaving other methods unrestricted, by enclosing the directives in a <Limit> section.

## Directives

- Allow
- Deny
- Order

See also Satisfy and Require.

## Allow directive

Syntax: Allow from all|host|env=env-variable [host|env=env-variable] ...
Context: directory, .htaccess
Override: Limit
Status: Base
Module: mod_access

The `Allow` directive affects which hosts can access an area of the server. Access can be controlled by hostname, IP Address, IP Address range, or by other characteristics of the client request captured in environment variables.

The first argument to this directive is always `from`. The subsequent arguments can take three different forms. If `Allow from all` is specified, then all hosts are allowed access, subject to the configuration of the `Deny` and `Order` directives as discussed below. To allow only particular hosts or groups of hosts to access the server, the host can be specified in any of the following formats:

A (partial) domain-name
  Example: `Allow from apache.org`
  Hosts whose names match, or end in, this string are allowed access. Only complete components are matched, so the above example will match `foo.apache.org` but it will not match `fooapache.org`. This configuration will cause the server to perform a double reverse DNS lookup on the client IP address, regardless of the setting of the HostnameLookups directive. It will do a reverse DNS lookup on the IP address to find the associated hostname, and then do a forward lookup on the hostname to assure that it matches the original IP address. Only if the forward and reverse DNS are consistent and the hostname matches will access be allowed.
A full IP address
  Example: `Allow from 10.1.2.3`
  An IP address of a host allowed access
A partial IP address
  Example: `Allow from 10.1`
  The first 1 to 3 bytes of an IP address, for subnet restriction.
A network/netmask pair
  Example: `Allow from 10.1.0.0/255.255.0.0`
  A network a.b.c.d, and a netmask w.x.y.z. For more fine-grained subnet restriction. (Apache 1.3 and later)
A network/nnn CIDR specification
  Example: `Allow from 10.1.0.0/16`
  Similar to the previous case, except the netmask consists of nnn high-order 1 bits. (Apache 1.3 and later)

Note that the last three examples above match exactly the same set of hosts.

The third format of the arguments to the `Allow` directive allows access to the server to be controlled based on the existence of an environment variable. When `Allow from env=`env-variable is specified, then the request is allowed access if the environment variable env-variable exists. The server provides the ability to set environment variables in a flexible way based on characteristics of the client request using the directives provided by mod_setenvif. Therefore, this directive can be used to allow access based on such factors as the clients `User-Agent` (browser type), `Referer`, or other HTTP request header fields.

Example:

>     SetEnvIf User-Agent ^KnockKnock/2.0 let_me_in
>     <Directory /docroot>
>         Order Deny,Allow
>         Deny from all
>         Allow from env=let_me_in
>     </Directory>

In this case, browsers with a user-agent string beginning with `KnockKnock/2.0` will be allowed access, and all others will be denied.

See also Deny, Order and SetEnvIf.

## Deny directive

Syntax: Deny from all|host|env=env-variable [host|env=env-variable] ...
Context: directory, .htaccess
Override: Limit
Status: Base
Module: mod_access

This directive allows access to the server to be restricted based on hostname, IP address, or environment variables. The arguments for the `Deny` directive are identical to the arguments for the Allow directive.

See also Allow, Order and SetEnvIf.

## Order directive

Syntax: Order ordering
Default: `Order Deny,Allow`
Context: directory, .htaccess
Override: Limit
Status: Base
Module: mod_access

The `Order` directive controls the default access state and the order in which Allow and Deny directives are evaluated. Ordering is one of

Deny,Allow
  The `Deny` directives are evaluated before the `Allow` directives. Access is allowed by default. Any client which does not match a `Deny` directive or does match an `Allow` directive will be allowed access to the server.
Allow,Deny
  The `Allow` directives are evaluated before the `Deny` directives. Access is denied by default. Any client which does not match an `Allow` directive or does match a `Deny` directive will be denied access to the server.
Mutual-failure
  Only those hosts which appear on the `Allow` list and do not appear on the `Deny` list are granted access. This ordering has the same effect as `Order Allow,Deny` and is deprecated in favor of that configuration.

Keywords may only be separated by a comma; no whitespace is allowed between them. Note that in all cases every `Allow` and `Deny` statement is evaluated.

In the following example, all hosts in the apache.org domain are allowed access; all other hosts are denied access.

> `Order Deny,Allow
> Deny from all
> Allow from apache.org
> `

In the next example, all hosts in the apache.org domain are allowed access, except for the hosts which are in the foo.apache.org subdomain, who are denied access. All hosts not in the apache.org domain are denied access because the default state is to deny access to the server.

> `Order Allow,Deny
> Allow from apache.org
> Deny from foo.apache.org
> `

On the other hand, if the `Order` in the last example is changed to `Deny,Allow`, all hosts will be allowed access. This happens because, regardless of the actual ordering of the directives in the configuration file, the `Allow from apache.org` will be evaluated last and will override the `Deny from foo.apache.org`. All hosts not in the `apache.org` domain will also be allowed access because the default state will change to allow.

The presence of an `Order` directive can affect access to a part of the server even in the absence of accompanying `Allow` and `Deny` directives because of its effect on the default access state. For example,

> `<Directory /www>
> Order Allow,Deny
> </Directory>`

will deny all access to the `/www` directory because the default access state will be set to deny.

The `Order` directive controls the order of access directive processing only within each phase of the server's configuration processing. This implies, for example, that an `Allow` or `Deny` directive occurring in a <Location> section will always be evaluated after an `Allow` or `Deny` directive occurring in a <Directory> section or `.htaccess` file, regardless of the setting of the `Order` directive. For details on the merging of configuration sections, see the documentation on How Directory, Location and Files sections work.

See also: Deny and Allow.

### Apache HTTP Server Version 1.3