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Tcl in packages/acs-kernel
Tcl in packages/acs-kernel
The goal of the Permissions system is to provide generic means to both programmers and site administrators to designate operations (methods) as requiring permissions, and then to check, grant, or revoke permissions via a consistent interface. For example, we might decide that the transaction that @@ -23,7 +23,7 @@ those package objects on which a user has certain permissions.
For site administrators and other authorized users, the Permissions UI provides a means to aggregate the primitive operations (methods) made available by the programmer into logical privileges (like read, write, and -admin) that can be granted and revoked.
In earlier versions of the OpenACS, permissions and access control was handled +admin) that can be granted and revoked.
In earlier versions of the OpenACS, permissions and access control was handled on a module-by-module basis, often even on a page-by-page basis. For example, a typical module might allow any registered user to access its pages read-only, but only allow members of a certain group to make changes. The way @@ -34,28 +34,28 @@ control were many, the two major ones being inconsistency, and repeated/redundant code. Thus the drive in OpenACS 4 to provide a unified, consistent permissions system that both programmers and administrators can -readily use.
The core of the permissions data model is quite simple. Unfortunately, the +readily use.
The core of the permissions data model is quite simple. Unfortunately, the hierarchical nature of default permissions entails quite a number of tree queries which could slow the system down. Since every page will have at least one permissions check, a number of views and auxiliary tables (de-normalizations of the data model) have been created to speed up access queries. As a consequence, speed of updates are decreased and requirements -for additional storage space increase.
As described in section V., the core of the permissions data model is +for additional storage space increase.
As described in section V., the core of the permissions data model is simple, though a number of views and auxiliary tables exist to ensure adequate performance. The core model consists of five tables:
The set of all defined methods.
The set of all defined privileges.
A relation describing the set of methods directly +
A relation describing the set of methods directly associated with each privilege.
A relation describing which privileges directly +
A relation describing which privileges directly "contain" other privileges.
A table with one (party, object, privilege) -row for every privilege directly granted on any object in +row for every privilege directly granted on any object in the system - this is a denormalization of acs_privilege_method_rules and acs_privilege_hierarchy
There are also a number of views to make it easier to ask specific @@ -78,7 +78,7 @@ a party is a member of a group (at any depth).
Relation with every (object, party, method) -tuple implied by the above trees.
In general, only acs_object_party_method_map +tuple implied by the above trees.
In general, only acs_object_party_method_map should be used for queries from other modules. The other views are intermediate steps in building that query.
The data model also includes two simple PL/SQL procedures (acs_permission.grant_permission and @@ -94,16 +94,16 @@ have taken methods from (at any level) (see acs_privilege_hierarchy)
objects get access control from direct grants, or inherit permissions from their context (unless the "don't inherit" flag is -set)
There are three essential areas in which all transactions in the -permissions system fall:
Modification of methods and privileges
Modification of permissions
Queries on permissions
"Modification of methods and privileges." This +set)
There are three essential areas in which all transactions in the +permissions system fall:
Modification of methods and privileges
Modification of permissions
Queries on permissions
"Modification of methods and privileges." This refers to actions that happen mainly at package installation time - a package will create a number of methods for its own use, then associate them with the system's standard privileges, or new privileges which the package has created. The association step might also happen later, if the site-wide administrator chooses to change permissions policy.
These steps involve directly manipulating the acs_methods, acs_privileges, and acs_privilege_method_rules tables. A web page for manipulating these features should be limited to site-wide -administrators.
"Modification of permissions" - involves fairly +administrators.
"Modification of permissions" - involves fairly common operations. Users are typically able to administer permissions for objects they themselves create. The two basic operations here are "grant" and "revoke". Granting permissions is done via @@ -112,7 +112,7 @@ acs_permissions table.
Web pages for making these changes are available to all users, so they should not be in an admin area. In order to grant and revoke permissions on an object, the user must have the administer_privileges method -permission on that object.
"Queries on permissions" - by far the most +permission on that object.
"Queries on permissions" - by far the most common operation is querying the permissions database. Several kinds of questions are commonly asked: First, and most commonly, "Can this party perform this method on this object?" Two Tcl functions are provided to @@ -126,16 +126,16 @@ against acs_object_party_method_map, or by calling the Tcl functions for appropriate methods.
Finally, when administering the permissions for an object, a web page needs to know all permissions directly granted on that object. This is done -by querying against acs_permissions.
The API to the permissions system consists of a few well-known tables, -plus a pair of PL/SQL procedures and a pair of Tcl functions.
Tables
acs_methods, acs_privileges, and +by querying against acs_permissions.
The API to the permissions system consists of a few well-known tables, +plus a pair of PL/SQL procedures and a pair of Tcl functions.
Tables
acs_methods, acs_privileges, and acs_privilege_method_rules manage the set of permissions in the system. At installation time, a package will add to these three tables to introduce new permissions into the system.
The main table for queries is acs_object_party_method_map, which contains (object, party, method) triples for all allowed operations in the system.
Also of interest for queries is acs_permissions, which lists directly granted privileges. Neither acs_object_party_method_map (which is a view) nor acs_permissions should be updated -directly.
PL/SQL Procedures
acs_permissions.grant_permission introduces new permissions for +directly.
PL/SQL Procedures
acs_permissions.grant_permission introduces new permissions for an object. It should be given an (object, party, privilege) triple, and will always succeed. If the permission is already in the system, no change occurs. The interface for this procedure @@ -154,14 +154,14 @@ privilege acs_permissions.privilege%TYPE );
These procedures are defined in -permissions-create.sql
Tcl Procedures
Two tcl procedures provide a simple call for the query, "Can this +permissions-create.sql
Tcl Procedures
Two tcl procedures provide a simple call for the query, "Can this user perform this method on this object?" One returns true or false, the other presents an error page.
To receive a true or false value, Tcl code should call:
ad_permission_p $object_id $object_type $method -user_id $user_id
If the user_id argument is left out, then the currently logged in user is checked. To create an error page, Tcl code should call:
ad_require_permission $object_id $object_type $method -
These procedures are defined in acs-permissions-procs.tcl.
All users of the permissions system are the same at the user-interface +
These procedures are defined in acs-permissions-procs.tcl.
All users of the permissions system are the same at the user-interface level. If you have the administer_privileges method permission on an object, then you may edit privileges for that object with the UI.
The UI currently provides a list of all granted permissions on the object. If the user wishes to revoke privileges, she may select a set of grants, @@ -173,15 +173,15 @@ one object" screen.
If it makes sense, the system will also display a checkbox which the user may select to toggle whether permissions are inherited from the object's context.
There are a number of potential future enhancements for the permissions -UI, outlined below.
The most important future changes to the Permissions system are likely to +UI, outlined below.
The most important future changes to the Permissions system are likely to be in the UI:
There should be a page displaying a list of all objects for which the current user is allowed to administer privileges.
Users should be able to view the permissions on any object, or perhaps on objects which they have the "read_permissions" method. This would allow them to see what grants are affecting their objects through -inheritance.
| Document Revision # | Action Taken, Notes | When? | By Whom? |
| 0.1 | Creation | 9/11/2000 | John Prevost |
| 0.2 | Edited for ACS 4 Beta release | 10/04/2000 | Kai Wu |
| Document Revision # | Action Taken, Notes | When? | By Whom? |
| 0.1 | Creation | 9/11/2000 | John Prevost |
| 0.2 | Edited for ACS 4 Beta release | 10/04/2000 | Kai Wu |