Apache Module mod_authz_core

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Description:	Core Authorization
Status:	Base
Module Identifier:	authz_core_module
Source File:	mod_authz_core.c
Compatibility:	Available in Apache HTTPD 2.3 and later

Summary

This module provides core authorization capabilities so that authenticated users can be allowed or denied access to portions of the web site. mod_authz_core provides the functionality to register various authorization providers. It is usually used in conjunction with an authentication provider module such as mod_authn_file and an authorization module such as mod_authz_user. It also allows for advanced logic to be applied to the authorization processing.

Topics

Creating Authorization Provider Aliases
Authorization Containers
The Require Directives

Comments

Creating Authorization Provider Aliases

Extended authorization providers can be created within the configuration file and assigned an alias name. The alias providers can then be referenced through the Require directive in the same way as a base authorization provider. Besides the ability to create and alias an extended provider, it also allows the same extended authorization provider to be referenced by multiple locations.

Example

The example below creates two different ldap authorization provider aliases based on the ldap-group authorization provider. This example allows a single authorization location to check group membership within multiple ldap hosts:

<AuthzProviderAlias ldap-group ldap-group-alias1 cn=my-group,o=ctx>
    AuthLDAPBindDN cn=youruser,o=ctx
    AuthLDAPBindPassword yourpassword
    AuthLDAPURL ldap://ldap.host/o=ctx
</AuthzProviderAlias>

<AuthzProviderAlias ldap-group ldap-group-alias2 cn=my-other-group,o=dev>
    AuthLDAPBindDN cn=yourotheruser,o=dev
    AuthLDAPBindPassword yourotherpassword
    AuthLDAPURL ldap://other.ldap.host/o=dev?cn
</AuthzProviderAlias>

Alias /secure /webpages/secure
<Directory /webpages/secure>
    Require all granted
    
    AuthBasicProvider file
    
    AuthType Basic
    AuthName LDAP_Protected_Place
    
    #implied OR operation
    Require ldap-group-alias1
    Require ldap-group-alias2
</Directory>

Authorization Containers

The authorization container directives <RequireAll>, <RequireAny> and <RequireNone> may be combined with each other and with the Require directive to express complex authorization logic.

The example below expresses the following authorization logic. In order to access the resource, the user must either be the superadmin user, or belong to both the admins group and the Administrators LDAP group and either belong to the sales group or have the LDAP dept attribute sales. Furthermore, in order to access the resource, the user must not belong to either the temps group or the LDAP group Temporary Employees.

<Directory /www/mydocs>
    <RequireAll>
        <RequireAny>
            Require user superadmin
            <RequireAll>
                Require group admins
                Require ldap-group cn=Administrators,o=Airius
                <RequireAny>
                    Require group sales
                    Require ldap-attribute dept="sales"
                </RequireAny>
            </RequireAll>
        </RequireAny>
        <RequireNone>
            Require group temps
            Require ldap-group cn=Temporary Employees,o=Airius
        </RequireNone>
    </RequireAll>
</Directory>

The Require Directives

mod_authz_core provides some generic authorization providers which can be used with the Require directive.

Require env

The env provider allows access to the server to be controlled based on the existence of an environment variable. When Require 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.

SetEnvIf User-Agent ^KnockKnock/2\.0 let_me_in
<Directory /docroot>
    Require 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.

When the server looks up a path via an internal subrequest such as looking for a DirectoryIndex or generating a directory listing with mod_autoindex, per-request environment variables are not inherited in the subrequest. Additionally, SetEnvIf directives are not separately evaluated in the subrequest due to the API phases mod_setenvif takes action in.

Require all

The all provider mimics the functionality that was previously provided by the 'Allow from all' and 'Deny from all' directives. This provider can take one of two arguments which are 'granted' or 'denied'. The following examples will grant or deny access to all requests.

Require all granted

Require all denied

Require method

The method provider allows using the HTTP method in authorization decisions. The GET and HEAD methods are treated as equivalent. The TRACE method is not available to this provider, use TraceEnable instead.

The following example will only allow GET, HEAD, POST, and OPTIONS requests:

Require method GET POST OPTIONS

The following example will allow GET, HEAD, POST, and OPTIONS requests without authentication, and require a valid user for all other methods:

<RequireAny>
     Require method GET POST OPTIONS
     Require valid-user
</RequireAny>

Require expr

The expr provider allows basing authorization decisions on arbitrary expressions.

Require expr "%{TIME_HOUR} -ge 9 && %{TIME_HOUR} -le 17"

<RequireAll>
    Require expr "!(%{QUERY_STRING} =~ /secret/)"
    Require expr "%{REQUEST_URI} in { '/example.cgi', '/other.cgi' }" 
</RequireAll>

Require expr "!(%{QUERY_STRING} =~ /secret/) && %{REQUEST_URI} in { '/example.cgi', '/other.cgi' }"

The syntax is described in the ap_expr documentation.

Normally, the expression is evaluated before authentication. However, if the expression returns false and references the variable %{REMOTE_USER}, authentication will be performed and the expression will be re-evaluated.

AuthMerging Directive

Description:	Controls the manner in which each configuration section's authorization logic is combined with that of preceding configuration sections.
Syntax:	`AuthMerging Off \| And \| Or`
Default:	`AuthMerging Off`
Context:	directory, .htaccess
Override:	AuthConfig
Status:	Base
Module:	mod_authz_core

When authorization is enabled, it is normally inherited by each subsequent configuration section, unless a different set of authorization directives is specified. This is the default action, which corresponds to an explicit setting of AuthMerging Off.

However, there may be circumstances in which it is desirable for a configuration section's authorization to be combined with that of its predecessor while configuration sections are being merged. Two options are available for this case, And and Or.

When a configuration section contains AuthMerging And or AuthMerging Or, its authorization logic is combined with that of the nearest predecessor (according to the overall order of configuration sections) which also contains authorization logic as if the two sections were jointly contained within a <RequireAll> or <RequireAny> directive, respectively.

The setting of AuthMerging is not inherited outside of the configuration section in which it appears. In the following example, only users belonging to group alpha may access /www/docs. Users belonging to either groups alpha or beta may access /www/docs/ab. However, the default Off setting of AuthMerging applies to the <Directory> configuration section for /www/docs/ab/gamma, so that section's authorization directives override those of the preceding sections. Thus only users belong to the group gamma may access /www/docs/ab/gamma.

<Directory /www/docs>
    AuthType Basic
    AuthName Documents
    AuthBasicProvider file
    AuthUserFile /usr/local/apache/passwd/passwords
    Require group alpha
</Directory>

<Directory /www/docs/ab>
    AuthMerging Or
    Require group beta
</Directory>

<Directory /www/docs/ab/gamma>
    Require group gamma
</Directory>

<AuthzProviderAlias> Directive

Description:	Enclose a group of directives that represent an extension of a base authorization provider and referenced by the specified alias
Syntax:	`<AuthzProviderAlias baseProvider Alias Require-Parameters> ... </AuthzProviderAlias>`
Context:	server config
Status:	Base
Module:	mod_authz_core

<AuthzProviderAlias> and </AuthzProviderAlias> are used to enclose a group of authorization directives that can be referenced by the alias name using the directive Require.

AuthzSendForbiddenOnFailure Directive

Description:	Send '403 FORBIDDEN' instead of '401 UNAUTHORIZED' if authentication succeeds but authorization fails
Syntax:	`AuthzSendForbiddenOnFailure On\|Off`
Default:	`AuthzSendForbiddenOnFailure Off`
Context:	directory, .htaccess
Status:	Base
Module:	mod_authz_core
Compatibility:	Available in Apache HTTPD 2.3.11 and later

If authentication succeeds but authorization fails, Apache HTTPD will respond with an HTTP response code of '401 UNAUTHORIZED' by default. This usually causes browsers to display the password dialogue to the user again, which is not wanted in all situations. AuthzSendForbiddenOnFailure allows to change the response code to '403 FORBIDDEN'.

Security Warning

Modifying the response in case of missing authorization weakens the security of the password, because it reveals to a possible attacker, that his guessed password was right.

Require Directive

Description:	Tests whether an authenticated user is authorized by an authorization provider.
Syntax:	`Require [not] entity-name [entity-name] ...`
Context:	directory, .htaccess
Override:	AuthConfig
Status:	Base
Module:	mod_authz_core

This directive tests whether an authenticated user is authorized according to a particular authorization provider and the specified restrictions. mod_authz_core provides the following generic authorization providers:

Require all granted: Access is allowed unconditionally.
Require all denied: Access is denied unconditionally.
Require env env-var [env-var] ...: Access is allowed only if one of the given environment variables is set.
Require method http-method [http-method] ...: Access is allowed only for the given HTTP methods.
Require expr expression: Access is allowed if expression evaluates to true.

Some of the allowed syntaxes provided by mod_authz_user, mod_authz_host, and mod_authz_groupfile are:

Require user userid [userid] ...: Only the named users can access the resource.
Require group group-name [group-name] ...: Only users in the named groups can access the resource.
Require valid-user: All valid users can access the resource.
Require ip 10 172.20 192.168.2: Clients in the specified IP address ranges can access the resource.

Other authorization modules that implement require options include mod_authnz_ldap, mod_authz_dbm, mod_authz_dbd, mod_authz_owner and mod_ssl.

In most cases, for a complete authentication and authorization configuration, Require must be accompanied by AuthName, AuthType and AuthBasicProvider or AuthDigestProvider directives, and directives such as AuthUserFile and AuthGroupFile (to define users and groups) in order to work correctly. Example:

AuthType Basic
AuthName "Restricted Resource"
AuthBasicProvider file
AuthUserFile /web/users
AuthGroupFile /web/groups
Require group admin

Access controls which are applied in this way are effective for all methods. This is what is normally desired. If you wish to apply access controls only to specific methods, while leaving other methods unprotected, then place the Require statement into a <Limit> section.

The result of the Require directive may be negated through the use of the not option. As with the other negated authorization directive <RequireNone>, when the Require directive is negated it can only fail or return a neutral result, and therefore may never independently authorize a request.

In the following example, all users in the alpha and beta groups are authorized, except for those who are also in the reject group.

<Directory /www/docs>
    <RequireAll>
        Require group alpha beta
        Require not group reject
    </RequireAll>
</Directory>

When multiple Require directives are used in a single configuration section and are not contained in another authorization directive like <RequireAll>, they are implicitly contained within a <RequireAny> directive. Thus the first one to authorize a user authorizes the entire request, and subsequent Require directives are ignored.

Security Warning

Exercise caution when setting authorization directives in Location sections that overlap with content served out of the filesystem. By default, these configuration sections overwrite authorization configuration in Directory, and Files sections.

The AuthMerging directive can be used to control how authorization configuration sections are merged.

<RequireAll> Directive

Description:	Enclose a group of authorization directives of which none must fail and at least one must succeed for the enclosing directive to succeed.
Syntax:	`<RequireAll> ... </RequireAll>`
Context:	directory, .htaccess
Override:	AuthConfig
Status:	Base
Module:	mod_authz_core

<RequireAll> and </RequireAll> are used to enclose a group of authorization directives of which none must fail and at least one must succeed in order for the <RequireAll> directive to succeed.

If none of the directives contained within the <RequireAll> directive fails, and at least one succeeds, then the <RequireAll> directive succeeds. If none succeed and none fail, then it returns a neutral result. In all other cases, it fails.

<RequireAny> Directive

Description:	Enclose a group of authorization directives of which one must succeed for the enclosing directive to succeed.
Syntax:	`<RequireAny> ... </RequireAny>`
Context:	directory, .htaccess
Override:	AuthConfig
Status:	Base
Module:	mod_authz_core

<RequireAny> and </RequireAny> are used to enclose a group of authorization directives of which one must succeed in order for the <RequireAny> directive to succeed.

If one or more of the directives contained within the <RequireAny> directive succeed, then the <RequireAny> directive succeeds. If none succeed and none fail, then it returns a neutral result. In all other cases, it fails.

Because negated authorization directives are unable to return a successful result, they can not significantly influence the result of a <RequireAny> directive. (At most they could cause the directive to fail in the case where they failed and all other directives returned a neutral value.) Therefore negated authorization directives are not permitted within a <RequireAny> directive.

<RequireNone> Directive

Description:	Enclose a group of authorization directives of which none must succeed for the enclosing directive to not fail.
Syntax:	`<RequireNone> ... </RequireNone>`
Context:	directory, .htaccess
Override:	AuthConfig
Status:	Base
Module:	mod_authz_core

<RequireNone> and </RequireNone> are used to enclose a group of authorization directives of which none must succeed in order for the <RequireNone> directive to not fail.

If one or more of the directives contained within the <RequireNone> directive succeed, then the <RequireNone> directive fails. In all other cases, it returns a neutral result. Thus as with the other negated authorization directive Require not, it can never independently authorize a request because it can never return a successful result. It can be used, however, to restrict the set of users who are authorized to access a resource.

Because negated authorization directives are unable to return a successful result, they can not significantly influence the result of a <RequireNone> directive. Therefore negated authorization directives are not permitted within a <RequireNone> directive.

Apache Module mod_authz_core

Summary

Directives

Topics

Creating Authorization Provider Aliases

Example

Authorization Containers

The Require Directives

Require env

Require all

Require method

Require expr

AuthMerging Directive

<AuthzProviderAlias> Directive

AuthzSendForbiddenOnFailure Directive

Security Warning

Require Directive

Security Warning

See also

<RequireAll> Directive

See also

<RequireAny> Directive

See also

<RequireNone> Directive

See also

Comments