Apache Module mod_access_compat

Summary

The directives provided bymod_access_compat 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 inenvironment variables. TheAllow andDeny directives are used to specify which clients are or are not allowed access to the server, while theOrder directive sets the default access state, and configures how theAllow andDeny directives interact with each other.

Both host-based access restrictions and password-based authentication may be implemented simultaneously. In that case, theSatisfy 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
• Satisfy

Bugfix checklist

• httpd changelog
• Known issues
• Report a bug

See also

• Require
• mod_authz_host
• mod_authz_core
• Comments

AllowDirective

TheAllow 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 alwaysfrom. The subsequent arguments can take three different forms. IfAllow from all is specified, then all hosts are allowed access, subject to the configuration of theDeny andOrder directives as discussed below. To allow only particular hosts or groups of hosts to access the server, thehost can be specified in any of the following formats:

A (partial) domain-name

Allow from example.orgAllow from .net example.edu

Hosts whose names match, or end in, this string are allowed access. Only complete components are matched, so the above example will matchfoo.example.org but it will not matchfooexample.org. This configuration will cause Apache httpd to perform a double DNS lookup on the client IP address, regardless of the setting of theHostnameLookups 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

Allow from 10.1.2.3Allow from 192.168.1.104 192.168.1.205

An IP address of a host allowed access

A partial IP address

Allow from 10.1Allow from 10 172.20 192.168.2

The first 1 to 3 bytes of an IP address, for subnet restriction.

A network/netmask pair

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.

A network/nnn CIDR specification

Allow from 10.1.0.0/16

Similar to the previous case, except the netmask consists of nnn high-order 1 bits.

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

IPv6 addresses and IPv6 subnets can be specified as shown below:

Allow from 2001:db8::a00:20ff:fea7:cceaAllow from 2001:db8::a00:20ff:fea7:ccea/10

The third format of the arguments to theAllow directive allows access to the server to be controlled based on the existence of anenvironment variable. WhenAllow from env=env-variable is specified, then the request is allowed access if the environment variableenv-variable exists. WhenAllow from env=!env-variable is specified, then the request is allowed access if the environment variableenv-variable doesn't exist. The server provides the ability to set environment variables in a flexible way based on characteristics of the client request using the directives provided bymod_setenvif. Therefore, this directive can be used to allow access based on such factors as the clientsUser-Agent (browser type),Referer, or other HTTP request header fields.

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 withKnockKnock/2.0 will be allowed access, and all others will be denied.

DenyDirective

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

OrderDirective

TheOrder directive, along with theAllow andDeny directives, controls a three-pass access control system. The first pass processes either allAllow or allDeny directives, as specified by theOrder directive. The second pass parses the rest of the directives (Deny orAllow). The third pass applies to all requests which do not match either of the first two.

Note that allAllow andDeny directives are processed, unlike a typical firewall, where only the first match is used. The last match is effective (also unlike a typical firewall). Additionally, the order in which lines appear in the configuration files is not significant -- allAllow lines are processed as one group, allDeny lines are considered as another, and the default state is considered by itself.

Ordering is one of:

Allow,Deny

First, allAllow directives are evaluated; at least one must match, or the request is rejected. Next, allDeny directives are evaluated. If any matches, the request is rejected. Last, any requests which do not match anAllow or aDeny directive are denied by default.

Deny,Allow

First, allDeny directives are evaluated; if any match, the request is deniedunless it also matches anAllow directive. Any requests which do not match anyAllow orDeny directives are permitted.

Mutual-failure

This order has the same effect asOrder Allow,Deny and is deprecated in its favor.

Keywords may only be separated by a comma;no whitespace is allowed between them.

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

Order Deny,AllowDeny from allAllow from example.org

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

Order Allow,DenyAllow from example.orgDeny from foo.example.org

On the other hand, if theOrder in the last example is changed toDeny,Allow, all hosts will be allowed access. This happens because, regardless of the actual ordering of the directives in the configuration file, theAllow from example.org will be evaluated last and will override theDeny from foo.example.org. All hosts not in theexample.org domain will also be allowed access because the default state isAllow.

The presence of anOrder directive can affect access to a part of the server even in the absence of accompanyingAllow andDeny 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 is set toDeny.

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

SatisfyDirective

Access policy if bothAllow andRequire used. The parameter can be eitherAll orAny. This directive is only useful if access to a particular area is being restricted by both username/passwordand client host address. In this case the default behavior (All) is to require that the client passes the address access restrictionand enters a valid username and password. With theAny option the client will be granted access if they either pass the host restriction or enter a valid username and password. This can be used to password restrict an area, but to let clients from particular addresses in without prompting for a password.

For example, if you wanted to let people on your network have unrestricted access to a portion of your website, but require that people outside of your network provide a password, you could use a configuration similar to the following:

Require valid-userAllow from 192.168.1Satisfy Any

Another frequent use of theSatisfy directive is to relax access restrictions for a subdirectory:

<Directory "/var/www/private">    Require valid-user</Directory><Directory "/var/www/private/public">    Allow from all    Satisfy Any</Directory>

In the above example, authentication will be required for the/var/www/private directory, but will not be required for the/var/www/private/public directory.

Since version 2.0.51Satisfy directives can be restricted to particular methods by<Limit> and<LimitExcept> sections.

See also

• Allow
• Require