bionic (5) dacs.acls.5.gz

Provided by: dacs_1.4.38a-2build1_amd64 bug

NAME

       dacs.acls - DACS access control rules

DESCRIPTION

       These files are part of the DACS suite.

       When DACS receives a service request, expressed as a URL (see RFC 1738[1], RFC 2396[2], and RFC 3986[3]),
       it invokes ACS (its access control service, dacs_acs(8)[4]) to determine whether the request should be
       carried out.  ACS defines a language in which access control specifications are written to describe the
       conditions under which access to a resource is to be granted or denied.

       When it is invoked, ACS is provided with the service request URI, its parameters (if any), the current
       credentials of the client, and certain environment-dependent variables. A simple protocol defines how the
       web server passes this information to ACS and how ACS passes its access control decision back to the web
       server (see dacs_acs(8)[4]).

       If access is not revoked for the client, ACS proceeds to search for an applicable ACL rule for the given
       request and client. It first searches through custom files (those configured for the jurisdiction through
       the virtual filestore's item type "acls"); if necessary, it will also look through a set of standard
       access control rules (those configured through the virtual filestore's item type "dacs_acls") in an
       attempt to find a closer match.

       This document describes access control rules and the DACS authorization procedure.

           Tip
           The dacsacl(1)[5] command is used to validate the syntax of the rulesets and to rebuild indexes.
           After changing a ruleset by adding, removing, or modifying a rule, dacsacl(1)[5] must be run.

   Revoking Access and Disabling Authentication: The Revocation List
       It is sometimes useful to have the administrative capability to "pull the plug" on a particular user,
       class of users, or depending on other context. This can be done in a "global" way by configuring a
       revocation list. The revocation list is consulted during authorization checking and by various
       authentication related components. The revocation list is processed by dacs_acs(8)[4] before the
       rulesets, thereby overriding all access control rules, to see if a request should be denied based on the
       current credentials (if any) associated with the user making the request. The revocation list is also
       used by dacs_authenticate(8)[6], dacs_auth_transfer(8)[7], and dacs_auth_agent(8)[8] immediately after a
       tentatively successful authentication to check if access has been revoked for the DACS identity
       established through the normal authentication procedure. Note that the revocation list is not used by
       dacsauth(1)[9] or dacscheck(1)[10] (although it arguably it should be, at least optionally).

       A revocation list must be configured through the item type "revocations" and must be readable, although
       it can be empty.

       The list consists of a sequence of lines, evaluated in the order in which they appear, each of which may
       contain:

       •   deny expression

           If the expression[11] evaluates to True, 1) access is denied and the user's request is not performed
           and 2) revocation list processing terminates

       •   revoke expression

           The expression[11] is evaluated once for each set of credentials; if the expression evaluates to
           True, 1) those credentials will be ignored in all subsequent processing of the current request (as if
           they did not exist), including the remainder of revocation list processing, 2) access is not
           necessarily denied, and 3) revocation list processing continues with the next line; in the case of an
           unauthenticated user, revoke has the same meaning as deny. Revoking all credentials makes the user
           unauthenticated with respect to this request. Note that this revocation does not affect any
           credentials held by the user, it only temporarily "hides" them.

               Note
               It is not currently possible to construct a single expression that tests multiple credentials. If
               this creates difficulties, consider using the ACS_CREDENTIALS_LIMIT[12] or AUTH_SINGLE_COOKIE[13]
               directive.

       •   disable expression

           The expression[11] is evaluated in a context that includes the tentative credentials. If it evaluates
           to True, the account is deemed to be disabled and the credentials will not be issued. This is the
           only keyword used specifically for disabling authentication and is ignored during access control
           processing.

       •   block expression

           This form combines deny and disable behaviour to both deny access and disable authentication,
           effectively blocking all access that satisfies the expression[11].

       •   a comment, where the first non-whitespace character, if any, is a '#'

       The keywords are case insensitive and one or more whitespace characters appear between a keyword and the
       expression. A line can be continued by ending it with a backslash. Any line may be preceded by whitespace
       characters.

       DACS expressions are described in dacs.exprs(5)[11].

       Examples:

           # Deny access to all
           deny user("any")

           # Deny access to any user not already authenticated
           # (subsequently no one will be able to authenticate)
           deny user("unauth")

           # Revoke all identities, making all users effectively unauthenticated
           revoke user("any")

           # Deny access to any user not authenticated by this jurisdiction
           deny user("unauth") or not user("${Conf::JURISDICTION_NAME}:")

           # Revoke the identity DSS:rmorriso
           revoke user("DSS:rmorriso")

           # Deny all access on the weekend
           deny time("wday") eq 6 or time("wday") eq 0

           # Deny any request not originating from a local network
           deny not (from("10.0.0.0/8") or from("192.168.2.0/24"))

           # Do not issue credentials to anyone from 10.0.0.124 but access is
           # still possible
           disable from("10.0.0.124")

           # Do not issue credentials to DSS:bobo
           disable user("DSS:bobo")

           # Neither issue credentials nor grant access to DSS:bobo
           block user("DSS:bobo")

   URL Paths and Service Name Matching
       While matching a service request against ACL rules, ACS recognizes a hierarchical structure for service
       names based on the path component of an HTTP (or HTTPS) URL. The URL path "/cgi-bin", for example, is
       considered to be an ancestor or parent of the path "/cgi-bin/program". The former URL path has two
       components, the latter has three components. The one-component URL path "/" is considered to be the
       ancestor of all other paths.

       The * operator, which matches zero or more components that follow it, has special meaning only when it
       appears as a path component at the end of a URL path pattern specified by a rule. A system administrator
       can use the tail matching (wildcard) capability to establish default rules for portions of the name space
       of service requests. For instance the URL path pattern "/cgi-bin/*" is considered to be the ancestor of
       all paths having the prefix "/cgi-bin/" and matches service requests for "/cgi-bin/printenv",
       "/cgi-bin/", and "/cgi-bin".

       Before matching a service request against the ruleset, ACS converts the service request into a canonical
       form. It strips any trailing / characters off of the service name (although the URL path pattern "/" is
       unchanged). Only absolute URLs can be specified in an ACL rule. The URL expressing the service request
       must also be absolute when received by DACS; typically, a web server will canonicalize the pathname
       corresponding to static content before ACS is invoked.

           Note
           It is the URL-encoded request URI (passed by Apache as ${DACS::URI}) that is matched against access
           control rules. Path components of URLs used for matching in rules are URL-decoded before being
           compared against the path components of the request URI, which are also URL-decoded.

       ACS searches the ruleset for the rule having the most specific URL path pattern that applies to a given
       request URI; that is, it examines the rules to find the one that has the greatest number of components in
       common with the service request's. If no exact match is found, it will search for increasingly general
       rules that apply. Only the most specific matching rule will be applied to the request; if it fails, no
       other (less specific) matching rule will be considered. If two or more rules "tie" (e.g., because of
       duplicate rules), one rule will be chosen arbitrarily. If no suitable match if found, ACS will deny
       access.

           Note
           The URL path pattern may not contain a query component; this may be changed in future versions.

       ACS does not recognize alternate names for the same resource (e.g., achieved using symbolic links), so it
       is possible for each of several names for the identical resource to be associated with different access
       control rules.

           Security
           It is not necessarily the case that permission to access a parent or any ancestor is required to
           access a descendent path.

       It should be emphasized that the service request URL received by the web server is textually matched
       against ACL rules without any interpretation on the part of ACS. Other than whether it will be mapped to
       static content or a CGI program, what the URL represents or how it will be processed by the web server is
       not taken into account by ACS.

       For example, a service request for "/weekly" is not the same as a service request for
       "/weekly/index.html", even if "/weekly" is a directory and the web server would map the request to a file
       named "/weekly/index.html" and return its contents. A rule with the URL path pattern "/weekly/index.html"
       or "/weekly/*" (or perhaps "/*") is needed to control access to the file "/weekly/index.html".

   Service Parameters
       A user agent may optionally pass parameters to CGI programs. With the HTTP GET method, the parameters are
       appended to the URL sent to the web server (the "query string") and the CGI program. While the HTTP
       specification (RFC 2616[14]) does not impose a limit on the length of a URL, a browser or web server may
       impose a maximum. (Recent versions of Internet Explorer have a maximum URL length of 2,083 bytes and the
       Apache web server imposes a limit of about 8192 bytes.) In the case of the HTTP POST method, the
       parameters are streamed from the user agent to the web server and then to the CGI program, so the
       potential number of parameters and their combined size is unbounded.  ACS can optionally provide a finer
       granularity of access control by inspecting the parameters passed with a service request. By examining
       parameters, an ACL rule can be used to prevent certain users from gaining particular kinds of access. A
       rule might restrict a parameter value to be within a certain allowed range, for example.  ACS supports
       expressions that may test whether particular service parameters are present or reference their values.

       Because in the case of the POST method it is impractical, in general, to pass ACS all parameters and
       their values, a web server may impose limits on the number of parameters and aggregate size of parameters
       that it will make available to ACS. An invoked CGI program is unaffected by this limitation, however.
       Apache's mod_auth_dacs[15] module allows its administrator to configure the maximum size of parameter
       data provided by the POST method that is made available to ACS.

   Constraints
       In some cases, merely testing parameter values is insufficient to determine whether access should be
       granted. Consider the case where a service is a program, a request's parameters represent the coordinates
       of a geographic area to be displayed, and some areas are not to be shown to some users, perhaps because
       they are "top secret". Examination of the parameters alone may be insufficient to determine whether the
       area they describe is within such a restricted area and perhaps ought not to be displayed. That
       determination might also depend on the contents of a database or complex calculations, for example. It
       is, therefore, beyond the scope of ACS to make access control decisions in such cases.

       ACS addresses this problem by allowing constraints to be attached to an ACL rule and by passing them, and
       the identity of the client, to the service. A constraint may be thought of as a tag or additional
       argument that a service recognizes. If an ACL rule permits the service to be invoked, it is the
       responsibility of the service to take any constraints into consideration and make the final decision
       about granting access, which it is much better qualified to do than is ACS. In the case previously
       described, a constraint might notify the service that the particular user should be granted access only
       if the request does not involve a restricted area.

       Of course, the purpose and meaning of a constraint depends on the implementation of a particular service.
       Different services might interpret the same constraint in completely different ways. For example, a
       service that performs both read-only operations and update operations might be implemented to recognize
       the constraint string "read-only" as meaning that it should only perform read-only operations.
       Alternatively, that same service might instead handle a request accompanied by the constraint string
       "updates-allowed" by permitting any operation for the user making the request; the absence of that
       constraint would restrict its functionality to read-only operations.

       For additional detail, please refer to descriptions of the DACS_CONSTRAINT and DACS_DEFAULT_CONSTRAINT
       environment variables.

   ACL Files
       Each access control rule is stored in a virtual filestore under the item types acls and dacs_acls. The
       acls must be configured, and ordinarily consists of site-specific or jurisdiction-specific rules; the
       latter (dacs_acls) is optional and is intended to configure rules for the standard DACS web services.

       The default configuration (from site.conf-std) is:

           VFS "[acls]dacs-fs:${Conf::FEDERATIONS_ROOT}/\
           ${Conf::FEDERATION_DOMAIN}/${Conf::JURISDICTION_NAME}/acls"
           VFS "[dacs_acls]dacs-fs:${Conf::DACS_HOME}/acls"

       Most installations store ACLs as ordinary files. This is reflected in the default configuration directive
       shown above and is why they are imprecisely referred to as "ACL files".

           Tip
           To make upgrading easier, avoid adding access control rules to dacs_acls (default location:
           /usr/local/dacs/acls) or modifying the default rules for DACS web services that appear there.
           Instead, put all customizations where acls has been configured. By following this practice, your
           customizations will not be lost when you install a new version of DACS.

       ACL Naming
           The names of ACL files (more precisely, the names of items within a virtual filestore) follow a
           particular convention: they must begin with the characters "acl-" (note: the fourth character is a
           hyphen, not an underscore) and end with a period followed by an unsigned integer value. At least one
           character must appear between the prefix and the suffix that begins with the period character. For
           example, any of the following names might be used:

               acl-photos.0
               acl-photos.1
               acl-files.40

               Tip
               Although not currently enforced, an ACL file name should be composed of characters from the
               Portable Filename Character Set[16]: any alphanumeric character, period, hyphen, or underscore.

           An ACL file may be disabled (not used by ACS) if a valid ACL filename is preceded by the characters
           "disabled-". The three ACLs above would be disabled if they were renamed as follows:

               disabled-acl-photos.0
               disabled-acl-photos.1
               disabled-acl-files.40

               Note
               These two filename prefixes are defined at compile time.  dacsacl(1)[5] should be enhanced to
               notice simultaneously enabled and disabled files.  FedAdmin, a contributed resource[17], is an
               administrative interface that can manage ACLs, including enabling, disabling, fetching, and
               deleting them.

           The numeric suffix is significant. It is used to order the evaluation of the rules by the access
           control service; the rules are evaluated in ascending order.

           Optionally, "subdirectories" (to any depth) can be created to help organize the access control rules.
           The naming convention for these subdirectories is the same as for ACL files. Disabling a subdirectory
           effectively disables all ACL files and subdirectories beneath it. The ordering process at each level
           is still based on the integer suffixes. Here is an example ordering of access control rules, from
           first to last:

               /usr/local/dacs/federations/dss/acls/acl-x.0
               /usr/local/dacs/federations/dss/acls/acl-x.2
               /usr/local/dacs/federations/dss/acls/acl-x.3/acl-y.7
               /usr/local/dacs/federations/dss/acls/acl-x.4
               /usr/local/dacs/federations/dss/acls/acl-x.5
               /usr/local/dacs/federations/dss/acls/acl-x.6/acl-x.1

           All ACL files and subdirectories that have invalid names are silently ignored, as are all files that
           are not regular files or directories (e.g., symbolic links). The behaviour is undefined if, for
           example, files named "acl-foo.0" and "disabled-acl-foo.0" exist simultaneously.

               Note
               Access control rules are ordinarily not placed in a location where a web server could serve them.
               If access control rules are themselves DACS-wrapped, however, care must be taken to structure the
               rules to avoid an infinite regress.

   ACL Syntax
       Basically, an ACL rule compactly expresses the triple (What, Who, How).

       What:
           the names of one or more services the rule applies to;

       Who
           the set of users the rule applies to; and

       How
           predicates and constraints that describe the conditions under which access will be allowed.

       Although it's certainly possible to write complicated access control rules, you needn't be intimidated.
       Rules are typically quite simple and easy to understand, such as the following rule which applies to a
       URL that has a path component ending in /cgi-bin/dacs/myprog.php and grants access to any authenticated
       user:

           <acl_rule status="enabled">
             <services>
               <service url_pattern="/cgi-bin/dacs/myprog.php"/>
             </services>

             <rule order="allow,deny">
                <allow>
                  user("auth")
                </allow>
             </rule>
           </acl_rule>

       An access control rule is written and stored externally as an XML document with the following DTD
       (acl.dtd[18]). Management of ACL rules can be done using a standard text editor, web-based interface, or
       special-purpose GUI. An administrator might only see a user-friendly description of the rules and need
       never see a lower-level representation such as this XML representation.

           <!ELEMENT acl_rule (services, (identity)*, (rule)+)>
           <!ATTLIST acl_rule
             status (enabled | disabled)             #IMPLIED
             name CDATA                              #IMPLIED
             expires_expr CDATA                      #IMPLIED
             constraint CDATA                        #IMPLIED
             permit_chaining (yes | no)              #IMPLIED
             pass_credentials (none | matched | all) #IMPLIED
             pass_http_cookie (yes | no)             #IMPLIED
             permit_caching (yes | no)               #IMPLIED
           >

           <!ELEMENT services (service | delegate)+>
           <!ATTLIST services
               shared (yes | no) #IMPLIED
           >

           <!ELEMENT service EMPTY>
           <!ATTLIST service
               id          CDATA #IMPLIED
               url_pattern CDATA #IMPLIED
               url_expr    CDATA #IMPLIED
           >

           <!ELEMENT delegate EMPTY>
           <!ATTLIST delegate
               id          CDATA #IMPLIED
               url_pattern CDATA #IMPLIED
               url_expr    CDATA #IMPLIED
               rule_uri    CDATA #REQUIRED
           >

           <!ELEMENT identity EMPTY>
           <!ATTLIST identity
               id            CDATA #IMPLIED
               iptr          CDATA #REQUIRED
               ident         CDATA #REQUIRED
               selector_expr CDATA #REQUIRED
           >

           <!ELEMENT rule ((precondition)?, (allow | deny)*) >
           <!ATTLIST rule
               id CDATA                                #IMPLIED
               order CDATA #REQUIRED
               <!-- order is either of: "allow,deny" or "deny,allow" -->
               constraint CDATA                        #IMPLIED
               permit_chaining (yes | no)              #IMPLIED
               pass_credentials (none | matched | all) #IMPLIED
               pass_http_cookie (yes | no)             #IMPLIED
               permit_caching (yes | no)               #IMPLIED
           >

           <!ELEMENT precondition ((user_list)?, (predicate)?)>

           <!ELEMENT user_list (user)*>

           <!ELEMENT user EMPTY>
           <!ATTLIST user
               id   CDATA #IMPLIED
               name CDATA #REQUIRED
           >

           <!ELEMENT predicate (#PCDATA)>

           <-- The allow element allows (grants) access, subject to the -->
           <-- allow,deny/deny,allow order, if the enclosed expression is TRUE -->
           <-- Note: any '<' and '&amp;' characters appearing within an allow element -->
           <-- must be escaped as &lt; and &amp;, respectively -->

           <!ELEMENT allow (#PCDATA)>
           <!ATTLIST allow
               id CDATA                                #IMPLIED
               constraint CDATA                        #IMPLIED
               permit_chaining (yes | no)              #IMPLIED
               pass_credentials (none | matched | all) #IMPLIED
               pass_http_cookie (yes | no)             #IMPLIED
               permit_caching (yes | no)               #IMPLIED
           >

           <-- The deny element denies access, subject to the allow,deny/deny,allow -->
           <-- order, if the enclosed expression is TRUE -->
           <-- Note: any '<' and '&amp;' characters appearing within an allow element -->
           <-- must be escaped as &lt; and &amp;, respectively -->

           <!ELEMENT deny (#PCDATA)>
           <!ATTLIST deny
               id CDATA                                #IMPLIED
           >

       The optional id attribute assigns a unique label (within its acl_rule) to an element so that it can be
       identified conveniently and unambiguously. Attribute values consist of one or more alphanumerics and
       underscores. At present, no other semantics are assigned to this attribute, but this may change in future
       releases. Labels that begin with an underscore are reserved for DACS-generated labels.

       General Structure
           An access control rule can be divided into two parts: an ordered list of service specifications (the
           services element) that are matched against service requests, and an ordered list of rule
           specifications (the rule elements) that are processed if and only if one of the service elements is
           applicable. In the event that the access control rule grants access, various aspects of subsequent
           processing can be controlled and defaults can be established.

       Services
           This part of the rule is used during rule selection. Each service element specifies a service to
           which this access control rule applies. The delegate element identifies a service that is handled by
           an access control rule specified elsewhere. Delegation is useful if parts of the URL space are
           managed by different users or if rules are stored in different locations.

       Rule Clause Processing
           An access control rule consists of one or more rule elements, also called rule clauses. A rule clause
           consists of allow and deny elements. The allow element allows (grants) access if the enclosed
           expression[11] is True, subject to the rule's order attribute. The deny element denies access if the
           enclosed expression is True, subject to the rule's order attribute.

           Each rule must have an order attribute that says whether the evaluation order is "allow,deny" or
           "deny,allow". This attribute serves much the same purpose as, and has semantics similar to, the
           Apache mod_authz_host[19] module's Order directive.

           The allow,deny ordering denies access by default and causes allow elements to be evaluated before
           deny elements. A request that does not satisfy an allow element or does satisfy a deny element will
           be denied. Equivalently, a request must satisfy an allow element but not satisfy any deny element for
           access to be granted. If a rule element has no allow element, it is processed as if it had an allow
           element that evaluated to False. If a rule element has no deny element, access is granted only if an
           allow element evaluates to True.

           The deny,allow ordering permits access by default and causes deny elements to be evaluated before
           allow elements. A request that does not satisfy a deny element or does satisfy an allow element will
           be allowed. Equivalently, a request must satisfy a deny element but not satisfy any allow element for
           access to be denied. If a rule element has no deny element, it is processed as if it had an deny
           element that evaluated to False. If a rule element has no allow element, access is granted only if no
           deny element evaluated to True.

           As soon as one allow (deny) element evaluates to True, no other elements of the same type are
           evaluated.

               Note
               Any '<' and '&' characters appearing within an allow element or a deny element must be escaped as
               "&lt;" and "&amp;", respectively.

       The Precondition Element
           A rule may optionally have exactly one precondition element. The precondition element is a "guard" to
           enable or disable a particular rule. This might be used, for example, to write one rule for weekdays
           and another for weekends. It can specify a list of users, an expression[11], or both. For the rule to
           be enabled for evaluation, its expression must first evaluate to True; if the user_list element is
           present, the user making the request must be among those listed and if the predicate is present, it
           must evaluate to True. The precondition primarily serves three purposes:

            1. it can make it clear which user(s) the rule applies to;

            2. it can improve by efficiency by avoiding having to evaluate potentially expensive expressions;
               and

            3. it provides a way to have multiple rule elements, any of which might be enabled depending on the
               run-time context.

       Expressions
           DACS employs expressions in access control rules and in configuration files (see dacs.exprs(5)[11]).
           For example, an expression or sequence of statements may appear within predicate, allow, and deny
           elements of an access control rule. If an expression (or sequence) evaluates to zero, the null
           string, or an error occurs, the result is False. If it evaluates to non-zero or a non-null string and
           no error occurs, the result of the expression (or sequence) is True. In general, arithmetic overflow
           and underflow, rounding, and other similar conditions will not be detected or considered as errors.

           The particular context within which a service request is being evaluated is made available to an
           expression through a set of variables. They are described with the dacs_acs(8)[4].

           Rules are examined in the order in which they are specified. If a precondition is False, processing
           continues with the next rule. The first rule with a True precondition will be used; no other rule
           will be examined. If no precondition element is given for a rule, it is equivalent to a precondition
           that evaluates to True. If no rule satisfies its precondition, access is denied.

       ACL Rule Elements
           The various syntactical components of access control rules are now described. When a request is being
           processed, ACS examines a ruleset, which is a collection of acl_rule elements that are located and
           accessed depending on the jurisdiction's configuration.

           DACS expressions are described in dacs.exprs(5)[11].

           acl_rule

                   <!ELEMENT acl_rule (services, (identity)*, (rule)+)>
                   <!ATTLIST acl_rule
                     status (enabled | disabled)             #IMPLIED
                     name CDATA                              #IMPLIED
                     expires_expr CDATA                      #IMPLIED
                     constraint CDATA                        #IMPLIED
                     permit_chaining (yes | no)              #IMPLIED
                     pass_credentials (none | matched | all) #IMPLIED
                     pass_http_cookie (yes | no)             #IMPLIED
                     permit_caching (yes | no)               #IMPLIED
                   >

               An acl_rule specifies, for a given set of services, the conditions under which a request for one
               of those services is to be granted (or denied). It may also establish new default behaviours
               (overriding compile-time or configuration defaults) that will be used unless they are in turn
               overridden during processing of this rule. The name attribute can be used to assign a symbolic
               name to the rule; some programs (e.g., dacsrlink(1)[20]) use this name to catch errors. The
               expires_expr attribute determines if the ACL should be ignored (and potentially deleted, although
               no DACS programs currently implement this). If the expression expires_expr evaluates to True, the
               rule should be deleted.

           identity

                   <!ELEMENT identity EMPTY>
                   <!ATTLIST identity
                       id            CDATA #IMPLIED
                       iptr          CDATA #REQUIRED
                       ident         CDATA #REQUIRED
                       selector_expr CDATA #REQUIRED
                   >

               This element associates a specified identity (ident) with the request during processing of this
               acl_rule only. This "assigned identity" overrides any identity or identities that were submitted
               with the request and is not tested for revocation. The iptr attribute is essentially a unique
               label for this element.

               The identity elements are examined, in the order in which they appear, until one element is
               selected; no other elements will be processed. An element is selected if its attribute
               (selector_expr), which is an expression[11], evaluates to True, in which case the identity
               specified by the ident attribute is used; its value must be a syntactically valid identity in the
               concise user syntax[21]. Access will be denied if an invalid identity is produced, and rule
               processing will proceed normally if no element is selected.

               The primary purpose of this element is to support an operational mode of the Rlinks[22] feature,
               but the capability may eventually be generalized. This element is subject to change. A future
               enhancement may allow the identity to alternatively be determined by expression evaluation.

           services

                   <!ELEMENT services (service | delegate)+>
                   <!ATTLIST services
                       shared (yes | no) #IMPLIED
                   >

               This element groups service and delegate elements.

           service

                   <!ELEMENT service EMPTY>
                   <!ATTLIST service
                       id          CDATA #IMPLIED
                       url_pattern CDATA #IMPLIED
                       url_expr    CDATA #IMPLIED
                   >

               To decide whether this acl_rule might apply to a request, ACS examines the set of one or more
               service elements. Each service element has either a url_pattern attribute or a url_expr attribute
               (but not both); the only difference is that the url_expr attribute is an expression[11] that is
               evaluated and converted to a string that is used internally as the url_pattern (it is a fatal
               error if the evaluation results in an error or the null string). Each effective url_pattern,
               whether given as a url_pattern attribute value or derived from a url_expr, is a simple pattern
               that may be matched against the URL of a service request. With the exception of the special '*'
               pattern, an effective url_pattern must begin with a '/'; its last component may be a '/*' to
               indicate that the pattern matches zero or more components of the service request URL that follow.

               The special '*' pattern always results in a successful exact match, causing rule searching to
               terminate immediately. It is useful as the value of a url_expr that has determined that its rule
               should be selected. Note that the semantics of this pattern are different from those of the
               pattern '/*', which results in a successful match only if no closer match is found.

               During matching, the URL of the service request is first stripped up to and including the
               hostname part, and parameters, if any, are excluded (starting with a '?' character and extending
               to the end). Any trailing '/' characters are removed.

               Consider the service request "/cgi-bin/metalogic/metalogic_groups" being matched against the
               following set of service elements:

                1. <service url_pattern="/*"/>

                2. <service url_pattern="/cgi-bin/*"/>

                3. <service url_pattern="/cgi-bin/metalogic/*"/>

                4. <service url_pattern="/cgi-bin/metalogic/metalogic_groups"/>

                5. <service url_pattern="/tmp/foo.gif"/>

               The first four prefixes match the service request URL, but the fourth url_pattern is selected
               since it is the most specific match, with the third url_pattern being the next most specific
               match.

               When a single site is home to more than one jurisdiction, it is often handy to be able to share
               access control rules among the jurisdictions. The shared attribute controls this behaviour. This
               is best described through an example. Consider the following (partial) Jurisdiction sections:

                   <Jurisdiction uri="dss.ca">
                     JURISDICTION_NAME "ANIMAL"
                   </Jurisdiction>

                   <Jurisdiction uri="dss.ca/dog">
                     JURISDICTION_NAME "DOG"
                   </Jurisdiction>

                   <Jurisdiction uri="dss.ca/cat">
                     JURISDICTION_NAME "CAT"
                   </Jurisdiction>

               With this feature enabled for a set of services, a request for dss.ca/cat/foo...  will only
               consider the /foo...  substring when searching the url_pattern attributes to find a matching
               rule.

               The syntax for the shared attribute is as follows:

                   <!-- Share all services among -->
                   <!-- path-differentiated jurisdictions -->
                   <services shared="yes">

                   <!-- Do not share services among -->
                   <!-- path-differentiated jurisdictions -->
                   <services shared="no">

                   <!-- Default: share all services among -->
                   <!-- path-differentiated jurisdictions -->
                   <services>

               Here are some examples, given the configuration above:

                   Partial request URI                 Matched url_pattern

                   dss.ca/cgi-bin/dacs/dacs_prenv      -->  /cgi-bin/dacs/dacs_prenv
                   dss.ca/dog/cgi-bin/dacs/dacs_prenv  -->  /cgi-bin/dacs/dacs_prenv
                   dss.ca/cat/cgi-bin/dacs/dacs_prenv  -->  /cgi-bin/dacs/dacs_prenv

                   Tip
                   The default behaviour is the same as if shared="yes" were specified. When this feature is
                   enabled, dss.ca/cat/cgi-bin/dacs/dacs_prenv will not match dss.ca/cgi-bin/dacs/dacs_prenv in
                   the example configuration above.

                   The default rules for DACS services assume the default behaviour with respect to sharing.

           delegate

                   <!ELEMENT delegate EMPTY>
                   <!ATTLIST delegate
                       id          CDATA #IMPLIED
                       url_pattern CDATA #IMPLIED
                       url_expr    CDATA #IMPLIED
                       rule_uri    CDATA #REQUIRED
                   >

               The delegate element functions exactly like the service element with respect to matching. Its
               purpose, however, is to redirect responsibility for subsequent access control processing for the
               request to another ruleset.

               There are many applications for this feature, but a common one is for a DACS administrator to
               "carve up" the URL space by delegating parts of it such that individual users are responsible for
               the rules governing their portion of the space. For example, URL paths that begin with /bob,
               /ted, and /ann might be delegated to rulesets found in /u/bob/.dacs/acls, /u/ted/.dacs/acls, and
               /u/ann/.dacs/acls, respectively, and a request like https://example.com/bob/index.html would be
               fielded by the ruleset found in /u/bob/.dacs/acls.

               If a delegate element is matched:

                1. no rule clauses in this access control rule will be examined

                2. any defaults specified in the acl_rule element will be discarded

                3. processing of the current ruleset is terminated

                4. the ruleset identified by the rule_uri attribute will be consulted

                5. no default system ACLs (dacs_acls) will be examined

               Processing of a delegated ruleset is performed in the same way as a non-delegated ruleset. A
               delegated ruleset may delegate some or all of its services to another ruleset; a maximum depth of
               three is enforced.

               Any error encountered during processing will cause access to be denied.

                   Note
                   Despite the attribute name, the value of the rule_uri attribute must currently be a defined
                   item type or a URL that identifies a directory or a supported database (i.e., having a URL
                   scheme of file, dacs-db, or dacs-ndbm) The semantics of this attribute are still being
                   considered.
               For example, an ACL with the elements:

                   <delegate url_pattern="/cgi-bin/myprog" rule_uri="my_acls"/>
                   <delegate url_pattern="/*" rule_uri="file:/u/bob/delegated"/>

               and the configuration:

                   VFS "[my_acls]dacs-db:/u/bob/my_acls.db"

               will delegate service requests matching the first element to rules found in the Berkeley DB file
               /u/bob/my_acls.db and all other service requests to a ruleset found in the directory
               /u/bob/delegated.

                   Security
                   Delegated access control rules have access to all functions (including exec()) and all
                   configuration information. Note that dacs_acs runs at the privilege level of Apache. For this
                   reason, be very careful how delegation is used. Log messages identify selection of delegated
                   rules and can be used to detect improper use. A future version of DACS should provide a way
                   to optionally restrict the abilities of delegated rules.

           rule

                   <!ELEMENT rule ((precondition)?, (allow | deny)*) >
                   <!ATTLIST rule
                       id CDATA                                #IMPLIED
                       order CDATA #REQUIRED
                       <!-- order is either of: "allow,deny" or "deny,allow" -->
                       constraint CDATA                        #IMPLIED
                       permit_chaining (yes | no)              #IMPLIED
                       pass_credentials (none | matched | all) #IMPLIED
                       pass_http_cookie (yes | no)             #IMPLIED
                       permit_caching (yes | no)               #IMPLIED
                   >

               Assuming that ACS has determined that this acl_rule is the one that best matches a request, it
               will then examine one or more of its rule elements and use the first one that has been enabled
               (that is, satisfies its precondition). An enabled rule element may establish new default
               behaviours (overriding compile-time, configuration, or acl_rule defaults) that will be used
               unless they are in turn overridden during processing of this rule.

               Information regarding rule clause processing[23] appeared earlier.

           precondition

                   <!ELEMENT precondition ((user_list)?, (predicate)?)>

               A precondition element is used to specify a set of users that includes the user making the
               request, a condition that must evaluate to True, or both.  ACS will examine the rule elements
               from top to bottom, selecting the first rule having a precondition that is satisfied. That rule
               is said to be enabled and no other rule will be considered. If no rule is enabled, access will be
               denied.

                   Note
                   A precondition element must contain a predicate element, a user_list element, or both.

           user_list, user

                   <!ELEMENT user_list (user)*>

                   <!ELEMENT user EMPTY>
                   <!ATTLIST user
                       id   CDATA #IMPLIED
                       name CDATA #REQUIRED
                   >

               A user_list element consists of zero or more user elements, each of which has a name attribute
               that is matched against the client's current credentials. Please refer to the description of the
               user()[24] function for details. A user_list that is absent or empty is effectively one that
               satisfies the precondition. It does not matter to ACS whether a mentioned user, group, or
               jurisdiction actually exists or is defined.

               The following is an example of a user_list (group names are prefixed by a '%' character):

                   <user_list>
                      <user name="DSS:smith"/>
                      <user name="%METALOGIC:admin/>
                      <user name="10.0.0.118"/>
                      <user name="192.168.0.0/24"/>
                      <user name="DACS:"/>
                      <user name="unauth"/>
                   </user_list>

           predicate

                   <!ELEMENT predicate (#PCDATA)>

               A predicate contains an expression[11] (or sequence of statements) that is evaluated in the
               context of a particular request and client's current credentials. A predicate having no
               expression evaluates to True. Expressions are described with dacs.exprs(5)[11]).

           allow

                   <!ELEMENT allow (#PCDATA)>
                   <!ATTLIST allow
                       id CDATA                                #IMPLIED
                       constraint CDATA                        #IMPLIED
                       permit_chaining (yes | no)              #IMPLIED
                       pass_credentials (none | matched | all) #IMPLIED
                       pass_http_cookie (yes | no)             #IMPLIED
                       permit_caching (yes | no)               #IMPLIED
                   >

               An allow element contains an expression[11] (or sequence of statements) that is evaluated in the
               context of a particular request and client's current credentials. If it evaluates to True, an
               allow element may establish particular behaviours (overriding compile-time or configuration
               defaults or encompassing acl_rule or rule element defaults). Information regarding rule clause
               processing[23] appeared earlier.

           deny

                   <!ELEMENT deny (#PCDATA)>
                   <!ATTLIST deny
                       id CDATA                                #IMPLIED
                   >

               A deny element contains an expression[11] (or sequence of statements) that is evaluated in the
               context of a particular request and client's current credentials. Information regarding rule
               clause processing[23] appeared earlier.

           If ACS grants access, various aspects of subsequent behaviour can be controlled through attributes of
           acl_rule elements, with attributes specified at a "deeper" level overriding ones encountered earlier
           during ruleset processing.

           A constraint can optionally be specified. If access is granted and a constraint has been provided by
           the particular allow element that evaluated to True, it is made available as the value of an
           environment variable named DACS_CONSTRAINT exported to the invoked CGI program. If access is granted
           and a default constraint has been provided, it is similarly made available as the value of an
           environment variable named DACS_DEFAULT_CONSTRAINT. Neither variable is defined if no value for it
           has been specified.

           If access is granted, ACS can be told through the pass_credentials attribute whether it should pass
           the user's current credentials on to the invoked service. For security reasons, it does not pass
           credentials ("none") by default. It can be instructed to pass all current credentials ("all"); a
           service such as dacs_current_credentials(8)[25], for example, needs to receive all of the current
           credentials. A third alternative is to pass only the current credentials of the identity that was
           used to grant access by having satisfied a user element ("matched"); in the case of multiple current
           credentials, it may not be possible to predict which current credentials will be matched. When
           permitted, credentials are passed in the same HTTP cookie format in which they were received as the
           value of the DACS_COOKIE environment variable.  DACS will look for the user's DACS cookies in that
           variable before checking the HTTP_COOKIE environment variable.

               Security
               Because environment variables are typically visible to all programs on a system, ACS "hobbles" or
               "weakens" credentials exported through them such that they can only be used in a few limited
               ways. Using them for access control purposes is not one of those ways, otherwise a DACS identity
               could easily be stolen by any user having access to the variables.

               In addition to the environment variable problem, a user might be tricked into invoking a service,
               though DACS-wrapped, that is under the control of an attacker. Weakening the credentials that are
               available to the service makes it difficult for the attacker to do any harm with them.

               A DACS administrator who understands the implications of visible credentials, and who still
               insists on proceeding at his own risk, can disable the DACS security measures by setting the
               permit_chaining attribute to yes. Any jurisdiction that should honor such credentials for access
               control purposes must set the configuration directive PERMIT_CHAINING[26] to yes. This will allow
               the credentials passed to a service invoked at that jurisdiction to be used for access control
               purposes. By default, this "chaining" or "cascading" behaviour is not permitted and the
               credentials are invalid for access control purposes.

               If the pass_credentials attribute is all or matched for the matching rule, unaltered credentials
               will be exported through the DACS_COOKIE environment variable.

           If access is granted, DACS can be told whether it should pass the Cookie header field to the invoked
           service. By default, pass_http_cookie is "no" to reduce the risk of cookies being exposed. Unless
           DACS has been configured with ALLOW_HTTP_COOKIE set to "yes", DACS services will refuse to operate if
           they receive a Cookie header field. If pass_http_cookie is "yes", however, the Cookie header field
           will be retained.

               Tip
               Setting pass_http_cookie to "yes" is often necessary in cases where Apache does an internal
               redirect, as when it invokes scripts through the Action[27] directive or when it automatically
               creates a directory index (as by the Indexes option of the Options[28] directive). If this
               attribute is not enabled, Apache will lose track of the identity associated with the request when
               the redirection occurs, and it will appear to DACS as if the user making the redirected request
               is not authenticated.

           The permit_caching attribute is used to indicate that positive access control decisions associated
           with the rule are eligible for caching. Please see Authorization Caching[29] for details.

           Groups are discussed in a separately in dacs.groups(5)[30].

   The ACL Selection and Evaluation Algorithm
       The following algorithm is used by ACS to determine if a particular service request (S, in canonical
       form) with optional parameters (P) should be granted for a user with verified credentials (C) within a
       particular execution environment (E). At this point, ACS has already determined that the revocation list
       has not denied access.

        1. ACS searches the ruleset for an acl_rule (R) that lists a service or delegation (using url_pattern or
           by evaluation of a url_expr) that most closely matches S. The list of services is examined in the
           order in which they appear.

           •   If any acl_rule matches exactly, it is selected and the search for an acl_rule is terminated; no
               other acl_rule in the current ruleset will be examined. Otherwise, the next acl_rule
               specification will be examined.

           •   The acl_rule elements in the ruleset are examined in increasing order of the integer suffix of
               each rule's name.

           •   A particular url_pattern should appear exactly once within the entire ruleset.

           ACS does not treat a duplicated url_pattern as an error, however, nor is it required to check for
           duplicates.

           If the closest match delegates responsibility to another ruleset, the procedure restarts by searching
           that ruleset.

        2. Each rule element in R is examined, from top to bottom, until all have been examined or until one is
           found that is enabled. An enabled rule either has no precondition element or has a precondition that
           evaluates to True. If an enabled rule is found, no other rule will be considered. If no enabled rule
           is found, access is denied.

           •   A precondition is True if the user is identified by a user element (or if there is no user_list
               element or no user element) and if the predicate element evaluates to True (or if there is no
               predicate element).

           •   During user_list processing, for each set of current credentials, the credentials are compared
               against the list of user elements in the order in which the user elements appear in the
               user_list.

           •   If there is more than one set of credentials accompanying the request, C is considered to be the
               union of all of the credentials.

           •   If the enabled rule specifies the order allow,deny, then allow elements are examined before deny
               elements; if the order is deny,allow, then deny elements are examined before allow elements.

           •   Evaluation of allow elements always stops when one evaluates to True.

           •   Evaluation of deny elements always stops when one evaluates to True.

           •   In the case of an allow,deny ordering, access is denied by default and allow elements are
               evaluated before deny elements; a request that does not satisfy an allow element or does satisfy
               a deny element will be denied.

           •   In the case of a deny,allow ordering, access is granted by default and causes deny elements to be
               evaluated before allow elements; a request that does not satisfy a deny element or does satisfy
               an allow element will be allowed.

           •   If any predicate evaluates to True, the user will be granted access to S with P.

        3. If access is granted, default or specific attributes associated with the matching acl_rule, rule, or
           allow elements will be passed to S.

           Security
           It is possible to construct rules such that more than one rule, allow, or deny element applies to a
           particular user or are contradictory. Such conditions are neither detected nor considered an error.

EXAMPLES

       For conciseness, some of the following examples omit the services element.

        1. This rule grants access to everyone because it establishes "allow" as the default and there is no
           satisfied deny element.

               <rule order="deny,allow"></rule>

        2. This rule denies access to everyone because it establishes "deny" as the default and there is no
           satisfied allow element.

               <rule order="allow,deny"></rule>

        3. This rule establishes the evaluation order allow,deny and there are two allow elements and no deny
           elements, which means that access will only be granted if one of the allow elements evaluates to
           True. The second allow element evaluates to True if 1) the variable SCALE is greater than 1000 and
           the user is authenticated or 2) the variable SCALE is greater than 10000 and the user is not
           authenticated.

               <rule order="allow,deny">
                 <allow>
                   user("METALOGIC:rmorriso") or user("DSS:brachman")
                 </allow>

                 <allow>
                   (${Args::SCALE} gt 1000 and user("auth"))
                      or (${Args::SCALE} gt 10000 and user("unauth"))
                 </allow>
               </rule>

           If the evaluation order deny,allow were selected instead, access would always be granted (since there
           is no deny element and the default is to grant access). If neither of the allow elements evaluates to
           True, however, default attributes (if present) would be in effect.

        4. If SCALE is less than 10000 and LAYER-ELEMENT is one of the listed layers and the user is not in the
           forest-inventory group, then deny. Otherwise, if the user is authenticated, allow.

               <rule order="allow,deny">
                 <deny>
                    ${Args::SCALE} lt 10000
                     and (${Args::LAYER-ELEMENT} eq "BC_ORTHO"
                     or ${Args::LAYER-ELEMENT} eq "BC_FC50K"
                     or ${Args::LAYER-ELEMENT} eq "AB_FC50K"
                     or ${Args::LAYER-ELEMENT} eq "SK_FC50K"
                     or ${Args::LAYER-ELEMENT} eq "MV_FC50K")
                     and (not user("%METALOGIC:forest-inventory-"))
                 </deny>

                 <allow>
                   user(auth)
                 </allow>
               </rule>

        5. The first of these rules is selected only for requests coming from members of the group
           METALOGIC:forest-inventory. Access is granted to any member, except METALOGIC:rmorriso. The second of
           these rules is selected for requests not coming from members of that group. Access is granted only if
           the condition is True.

               <rule order="allow,deny">
                 <precondition>
                   <user_list>
                     <user name="%METALOGIC:forest-inventory"/>
                   </user_list>
                 </precondition>

                 <allow>
                   not user("METALOGIC:rmorriso")
                 </allow>
               </rule>

               <rule order="allow,deny">
                 <allow>
                   ( ${Args::SCALE} gt 1000 and user("auth") )
                     or ( ${Args::SCALE} gt 10000 and user("unauth") )
                 </allow>
               </rule>

           If the first rule's precondition were instead:

               <precondition>
                 <predicate>
                   user("%METALOGIC:forest-inventory") and user("DSS:")
                 </predicate>
               </precondition>

           then the first rule would only be considered if the user belonged to that group and he was
           authenticated by the DSS jurisdiction.

        6. This rule establishes a default for all CGI programs under the cgi-bin URL space. Only users
           authenticated by the jurisdiction METALOGIC will have access and CGI programs will be invoked with
           the environment variable DACS_DEFAULT_CONSTRAINT set to "MODE=execute-only".

               <acl_rule status="enabled" constraint="MODE=execute-only">
                  <services>
                    <service url_pattern="/cgi-bin/*"/>
                  </services>
                  <rule order="allow,deny">
                    <precondition>
                      <user_list>
                        <user name="METALOGIC:"/>
                      </user_list>
                    </precondition>
                    <allow>
                    </allow>
                  </rule>
               </acl_rule>

        7. This rule establishes a default behaviour that denies all access.

               <acl_rule status="enabled">
                 <services>
                    <service url_pattern="/*"/>
                 </services>
                 <rule order="allow,deny">
                   <deny>
                   </deny>
                 </rule>
               </acl_rule>

        8. This rule establishes a default behaviour that grants access to the URL space under /any-user to any
           authenticated user. CGI programs will be invoked with the environment variable DACS_CONSTRAINT set to
           "read-only".

               <acl_rule status="enabled">
                 <services>
                    <service url_pattern="/any-user/*"/>
                 </services>
                 <rule order="allow,deny">
                    <allow constraint="read-only">
                      user("auth")
                    </allow>
                 </rule>
               </acl_rule>

        9. This rule establishes a default for all CGI programs under the cgi-bin/gis and cgi-bin/metalogic URL
           space. Access is granted to members of the groups BC:gis and NF:gis only if the value of parameter X
           is greater than 10 and the value of parameter Y is greater than 17. CGI programs invoked by those
           users will have the environment variable DACS_DEFAULT_CONSTRAINT set to "MODE=read-only". Members of
           the group ON:gis have no constraints on the parameters and will invoke CGI programs with the
           environment variable DACS_CONSTRAINT set to "read-write". Requests that do not meet either allow
           element will be denied.

               <acl_rule status="enabled" constraint="read-only">
                 <services>
                    <service url_pattern="/cgi-bin/gis/*"/>
                    <service url_pattern="/cgi-bin/metalogic/*"/>
                 </services>

                 <rule order="allow,deny">
                   <allow>
                     ${Args::X} gt 10 and ${Args::Y} gt 17
                        and (user("%BC:gis") or user("%NF:gis")
                   </allow>

                   <allow constraint="read-write">
                      user("%ON:gis")
                   </allow>
                 </rule>
               </acl_rule>

       10. Only bob@dss.ca, authenticated by jurisdiction DSS, will have access to the service
           /cgi-bin/bob-prog.cgi.

               <acl_rule status="enabled">
                  <services>
                    <service url_pattern="/cgi-bin/bob-prog.cgi"/>
                  </services>

                  <rule order="allow,deny">
                    <allow>
                      user("DSS:bob@dss.ca")
                    </allow>
                  </rule>
               </acl_rule>

       11. Every user will be able to invoke the service /cgi-bin/metalogic/group if CGI parameter OP is
           LIST_GROUPS or SHOW_GROUP. If OP is ADD_GROUP, DELETE_GROUP, or MODIFY_GROUP, only a member of the
           group DSS:admin can invoke the program. String comparisons are performed without regard to case. If
           OP has any other value, access will be denied.

               <acl_rule status="enabled">
                  <services>
                    <service url_pattern="/cgi-bin/metalogic/group"/>
                  </services>

                  <rule order="allow,deny">
                    <allow>
                      ${Args::OP} eq:i "LIST_GROUPS"
                         or ${Args::OP} eq:i "SHOW_GROUP"
                    </allow>

                    <allow>
                      (${Args::OP} eq:i "ADD_GROUP"
                         or ${Args::OP} eq:i "DELETE_GROUP"
                         or ${Args::OP} eq:i "MODIFY_GROUP")
                         and user("%DSS:admin")
                    </allow>
                 </rule>
               </acl_rule>

SEE ALSO

       dacsacl(1)[5], dacs_admin(8)[31]

AUTHOR

       Distributed Systems Software (www.dss.ca[32])

COPYING

       Copyright2003-2013 Distributed Systems Software. See the LICENSE[33] file that accompanies the
       distribution for licensing information.

NOTES

        1. RFC 1738
           http://www.rfc-editor.org/rfc/rfc1738.txt

        2. RFC 2396
           http://www.rfc-editor.org/rfc/rfc2396.txt

        3. RFC 3986
           http://www.rfc-editor.org/rfc/rfc3986.txt

        4. dacs_acs(8)
           http://dacs.dss.ca/man/dacs_acs.8.html

        5. dacsacl(1)
           http://dacs.dss.ca/man/dacsacl.1.html

        6. dacs_authenticate(8)
           http://dacs.dss.ca/man/dacs_authenticate.8.html

        7. dacs_auth_transfer(8)
           http://dacs.dss.ca/man/dacs_auth_transfer.8.html

        8. dacs_auth_agent(8)
           http://dacs.dss.ca/man/dacs_auth_agent.8.html

        9. dacsauth(1)
           http://dacs.dss.ca/man/dacsauth.1.html

       10. dacscheck(1)
           http://dacs.dss.ca/man/dacscheck.1.html

       11. expression
           http://dacs.dss.ca/man/dacs.exprs.5.html

       12. ACS_CREDENTIALS_LIMIT
           http://dacs.dss.ca/man/dacs.conf.5.html#ACS_CREDENTIALS_LIMIT

       13. AUTH_SINGLE_COOKIE
           http://dacs.dss.ca/man/dacs.conf.5.html#AUTH_SINGLE_COOKIE

       14. RFC 2616
           http://www.rfc-editor.org/rfc/rfc2616.txt

       15. mod_auth_dacs
           http://dacs.dss.ca/man/mod_auth_dacs.html

       16. Portable Filename Character Set
           http://www.opengroup.org/onlinepubs/009695399/basedefs/xbd_chap03.html#tag_03_276

       17. contributed resource
           http://sourceforge.net/projects/dacs-contrib/

       18. acl.dtd
           http://dacs.dss.ca/man/../dtd-xsd/acl.dtd

       19. mod_authz_host
           http://httpd.apache.org/docs/2.2/mod/mod_authz_host.html

       20. dacsrlink(1)
           http://dacs.dss.ca/man/dacsrlink.1.html

       21. concise user syntax
           http://dacs.dss.ca/man/dacs.1.html#concise_user_syntax

       22. Rlinks
           http://dacs.dss.ca/man/dacs_acs.8.html#rlinks

       23. rule clause processing
           http://dacs.dss.ca/man/#ordering

       24. user()
           http://dacs.dss.ca/man/dacs.exprs.5.html#user

       25. dacs_current_credentials(8)
           http://dacs.dss.ca/man/dacs_current_credentials.8.html

       26. PERMIT_CHAINING
           http://dacs.dss.ca/man/dacs.conf.5.html#PERMIT_CHAINING

       27. Action
           http://httpd.apache.org/docs/2.2/mod/mod_actions.html#action

       28. Options
           http://httpd.apache.org/docs/2.2/mod/core.html#options

       29. Authorization Caching
           http://dacs.dss.ca/man/dacs_acs.8.html#authorization_caching

       30. dacs.groups(5)
           http://dacs.dss.ca/man/dacs.groups.5.html

       31. dacs_admin(8)
           http://dacs.dss.ca/man/dacs_admin.8.html

       32. www.dss.ca
           http://www.dss.ca

       33. LICENSE
           http://dacs.dss.ca/man/../misc/LICENSE