Role-Based Group Membership

Jurisdictions, such as companies or organizations, typically have a hierarchical internal structure, perhaps based on subdivisions such as departments, groups, projects, and so on. Typically, an individual is associated with one or more of these subdivisions. Alternatively, jurisdictions might use an organizational structure that is based on the role of each individual.

Regardless of the type of structure, jurisdictions may have information services that describe and manage where an individual belongs within that structure. A directory system, such as X.500 or Microsoft's Active Directory, which is typically accessible using the Lightweight Directory Access Protocol (LDAP), is a common example of such an information service. Another example is found in Unix-type systems, which assign their users to groups for access control purposes. By exporting this information, or by creating and managing its own group definitions, a jurisdiction can use DACS to provide role-based security.

DACS uses the concept of a role-based group to allow a jurisdiction to implicitly create groups and associate users with them. At authentication time, a jurisdiction can indicate which roles a user belongs to within the jurisdiction. This information becomes part of the user's credentials and is consulted when determining whether the user is a member of a given group. The entire membership of a role-based group, potentially very large and possibly sensitive, need never be revealed or distributed to other jurisdictions.

Group information may sometimes be extracted from a directory system by processing the distinguished names of users. Consider a distinguished name like the following, which might be retrieved from a directory system:

{cou=CA, prov=BC, o=BigBank, ou=RandD, ou=Software, ou=Networks, cn=Auggie Doggie}

For this individual, a role descriptor asserting membership in three groups within the jurisdiction might be produced: 1) RandD, 2) Software within RandD, and 3) Networks within Software under RandD. Within DACS access control rules, these groups might be referred to as "%BigBank:RandD", "%BigBank:RandD-Software", and "%BigBank:RandD-Software-Networks", respectively. These group names may also be included in the membership of other groups. Also, a group having one of these names can be defined and administered using DACS's standard group membership methods; its membership is the union of the role-based group members and the explicitly named group members.

A concise syntax is available for expressing hierarchically-related elements of a role descriptor. The role descriptor "RandD/Software/Networks" is an equivalent way of expressing the three-element descriptor given above.

It is relatively easy for a jurisdiction to use its existing services to export the required role description to DACS. The Roles clause (see dacs.conf(5)) configures how this is done.

Group Syntax and Semantics

The following BNF syntax describes the names and symbols used in group definitions. Upper and lower case are distinct in the defined strings and all strings are constructed from a subset of the printable ASCII characters (e.g., the group name DSS:abc is different from the group name DSS:AbC).

<Jurisdiction-Name>       ::= [A-Za-z][A-Za-z0-9\-_]*
<Jurisdiction-Group-Name> ::= [A-Za-z][A-Za-z0-9\-_]*

Thus, jurisdiction names and group names are composed of upper and lower case letters, digits, dashes, and underscores and must begin with a letter.

The name of a group is formed from two components:

<Group-Name> ::= <Jurisdiction-Name> ':' <Jurisdiction-Group-Name>

The <Jurisdiction-Name> is the unique, officially-assigned abbreviated name for the DACS jurisdiction. The <Jurisdiction-Group-Name> is a unique name for the group within the jurisdiction that defines the <Group-Name>.

The following XML DTD is used as the external representation of group definitions and membership. It is used by DACS both to distribute this information from one jurisdiction to another.

<!ELEMENT groups (group_definition)* >

<!ELEMENT group_definition (group_member*) >
<!ATTLIST group_definition
    jurisdiction    CDATA #REQUIRED
    name            CDATA #REQUIRED
    mod_date        CDATA #REQUIRED
    type            (public | private) #REQUIRED
>

<!ELEMENT group_member EMPTY >
<!ATTLIST group_member
    jurisdiction    CDATA #REQUIRED
    name            CDATA #REQUIRED
    alt_name        CDATA #IMPLIED
    type            (role | dacs | username | meta) #REQUIRED
    dacs_url        CDATA #IMPLIED
    authenticates   (yes | no) #IMPLIED
    prompts         (yes | no) #IMPLIED
    auxiliary       CDATA #IMPLIED
>

A group_definition gives the official name of the jurisdiction that defined the group (jurisdiction), a name for the group that is unique with that jurisdiction (name), the date and time the group's definition was last changed (mod_date) and whether the group's membership is to be kept private (type). The date and time are expressed in UTC and using a 24 hour clock, in the format Wdy, DD-Mon-YYYY HH:MM:SS GMT, based on RFC 822, with the variations that the only legal time zone is GMT and the separators between the elements of the date must be dashes. If public, the type attribute indicates that the group membership may be distributed to other jurisdictions and included in the definition of another group that is distributed.

Each group_member specifies a member of the group. The type is role if the named member is a role, username if it is a DACS username, and dacs if it is the name of another DACS group. The special type meta is reserved for the internal use of DACS and associated with this type only is the presence of information about the jurisdiction: dacs_url, name, altname, authenticates, and prompts, each of which must be present for this type, and auxiliary, which is optional. Refer to DACS Metadata for additional information.

<group_member jurisdiction="METALOGIC" name="Metalogic"
  type="meta" alt_name="Metalogic Software Corp."
  dacs_url="%2+/metalogic/dacs" authenticates="yes"
 prompts="no" auxiliary="local" />

http://test-03.example.com/fedadmin/dacs/dacs_list_jurisdictions

http://test-03.example.com/metalogic/dacs 

<group_member jurisdiction="DACS" name="DSS Inc." type="meta"
 alt_name="DSS Inc." dacs_url="%0:%p/cgi-bin/dacs" authenticates="yes"
 prompts="no" auxiliary="local" />

https://dacs.dss.ca:8443/cgi-bin/dacs/dacs_list_jurisdictions

https://dacs.dss.ca:8443/cgi-bin/dacs

If the type is role, any user who has credentials that name the given role is a member of the group.

The appearance of a group name in the membership list of a group definition effectively inserts the entire membership of that referenced group in the definition. This type of inclusion is recursive, allowing for a configurable maximum depth. A cycle of inclusions is detected and not considered an error. Duplicate members are culled from the final membership list. All invalid group definitions are considered by DACS to have no members (that is, they are treated as having an empty membership list). The included group may belong to the same jurisdiction as the one being defined or it may refer to a group defined by some other jurisdiction. In the latter case, the administrator who defines the group delegates part of the responsibility for the group definition to another administrator who might do the same.

A group may be defined to be empty (i.e., not having any members).

DACS Metadata

At each jurisdiction in a federation, DACS requires metadata that describes the jurisdictions. This information might be used by middleware or client-side software, for instance, for creating a menu to present to the user, which would need to obtain a list of jurisdictions. The metadata is also used for various internal purposes.

Group information about jurisdictions is indicated by the meta attribute value for the type attribute.

This example group definition describes a four jurisdiction DACS federation:

<groups>
  <group_definition
    jurisdiction="DACS" name="jurisdictions" mod_date="Tue, 11-Sep-2001 3:00:00 GMT" type="public">

  <group_member jurisdiction="METALOGIC"
    name="Full name of this jurisdiction, in English"
    alt_name="Full name of this jurisdiction, in French"
    type="meta"
    dacs_url="http://metalogic.example.com/cgi-bin"
    authenticates="yes"
    prompts="no" />

  <group_member jurisdiction="BC"
    name="Full name of this jurisdiction, in English"
    alt_name="Full name of this jurisdiction, in French"
    type="meta"
    dacs_url="http://bc.example.com/cgi-bin"
    authenticates="yes"
    prompts="no" />

  <group_member jurisdiction="ON"
    name="Full name of this jurisdiction, in English"
    alt_name="Full name of this jurisdiction, in French"
    type="meta"
    dacs_url="http://on.example.com/cgi-bin/dacs"
    authenticates="yes"
    prompts="no" />

  <group_member jurisdiction="NF"
    name="Full name of this jurisdiction, in English"
    alt_name="Full name of this jurisdiction, in French"
    type="meta"
    dacs_url="http://nf.example.com/cgi-bin"
    authenticates="yes"
    prompts="yes" />

  </group_definition>
</groups>