DACS.ACLS(5)                  DACS Formats Manual                 DACS.ACLS(5)

       dacs.acls - DACS access control rules

       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

           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:

       •   denyexpression

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

       •   revokeexpression

           The expression 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.

               It is not currently possible to construct a single expression
               that tests multiple credentials. If this creates difficulties,
               consider using the ACS_CREDENTIALS_LIMIT[11] or
               AUTH_SINGLE_COOKIE[12] directive.

       •   disableexpression

           The expression 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.

       •   blockexpression

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

       •   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

       DACS expressions are described in dacs.exprs(5)[13].


           # 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("") or from(""))

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

           # 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.

           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.

           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.

           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

       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

       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:${Conf::FEDERATIONS_ROOT}/\
           VFS "[dacs_acls]dacs-fs:${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".

           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:


               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

           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:


               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

           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:


           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

               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).

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

           the set of users the rule applies to; and

           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">
               <service url_pattern="/cgi-bin/dacs/myprog.php"/>

             <rule order="allow,deny">

       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.

           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 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
           Apachemod_access[19] module's Order directive.

           The allow,deny ordering denies access by default and causes allow
           elements to be evaluated beforedeny 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

           The deny,allow ordering permits access by default and causes deny
           elements to be evaluated beforeallow 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

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

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

       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, 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.

           DACS employs expressions in access control rules and in
           configuration files (see dacs.exprs(5)[13]). 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 Trueprecondition 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)[13].


                   <!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.


                   <!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

               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, 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.


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

               This element groups service and delegate elements.


                   <!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 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

               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

                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

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

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

               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

               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 -->

               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

                   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

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


                   <!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

                2. any defaults specified in the acl_rule element will be

                3. processing of the current ruleset is terminated

                4. the ruleset identified by the rule_uri attribute will be

                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

                   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

                   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.


                   <!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


                   <!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.

                   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 name="DSS:smith"/>
                      <user name="%METALOGIC:admin/>
                      <user name=""/>
                      <user name=""/>
                      <user name="DACS:"/>
                      <user name="unauth"/>


                   <!ELEMENT predicate (#PCDATA)>

               A predicate contains an expression (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


                   <!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 (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.


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

               A deny element contains an expression (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.

               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

               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.

               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

           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

           •   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

           •   Evaluation of allow elements always stops when one evaluates to

           •   Evaluation of deny elements always stops when one evaluates to

           •   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.

           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.

       For conciseness, some of the following examples omit the services

        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

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

                   (${Args::SCALE} gt 1000 and user("auth"))
                      or (${Args::SCALE} gt 10000 and user("unauth"))

           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">
                    ${Args::SCALE} lt 10000
                     and (${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-"))


        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">
                     <user name="%METALOGIC:forest-inventory"/>

                   not user("METALOGIC:rmorriso")

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

           If the first rule's precondition were instead:

                   user("%METALOGIC:forest-inventory") and user("DSS:")

           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

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

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

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

        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">
                    <service url_pattern="/any-user/*"/>
                 <rule order="allow,deny">
                    <allow constraint="read-only">

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

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

                   <allow constraint="read-write">

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

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

                  <rule order="allow,deny">

       11. Every user will be able to invoke the service
           /cgi-bin/metalogic/group if CGI parameter OP is LIST_GROUPS or
           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">
                    <service url_pattern="/cgi-bin/metalogic/group"/>

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

                      (${Args::OP} eq:i "ADD_GROUP"
                         or ${Args::OP} eq:i "DELETE_GROUP"
                         or ${Args::OP} eq:i "MODIFY_GROUP")
                         and user("%DSS:admin")

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

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

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

        1. RFC 1738

        2. RFC 2396

        3. RFC 3986

        4. dacs_acs(8)

        5. dacsacl(1)

        6. dacs_authenticate(8)

        7. dacs_auth_transfer(8)

        8. dacs_auth_agent(8)

        9. dacsauth(1)

       10. dacscheck(1)



       13. dacs.exprs(5)

       14. RFC 2616

       15. mod_auth_dacs

       16. Portable Filename Character Set

       17. contributed resource

       18. acl.dtd

       19. mod_access

       20. dacsrlink(1)

       21. concise user syntax

       22. Rlinks

       23. rule clause processing

       24. user()

       25. dacs_current_credentials(8)


       27. Action

       28. Options

       29. Authorization Caching

       30. dacs.groups(5)

       31. dacs_admin(8)

       32. www.dss.ca

       33. LICENSE

DACS 1.4.28b                      02/04/2014                      DACS.ACLS(5)