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An authorization Rails plugin using a declarative DSL for specifying authorization rules in one place
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= Declarative Authorization

The declarative authorization plugin offers an authorization mechanism inspired 
by _RBAC_.  The most notable distinction to existing authorization plugins is the 
declarative authorization approach.  That is, authorization rules are not 
programmatically in between business logic but in an authorization configuration.

Currently, Rails authorization plugins only provide for programmatic 
authorization rules.  That is, the developer needs to specify which roles are 
allowed to access a specific controller action or a part of a view, which is
not DRY.  With a growing application code base and functions, as it happens 
especially in agile development processes, it may be decided to introduce new 
roles.  Then, at several places of the source code the new group needs to be 
added, possibly leading to omissions and thus hard to test errors.  Another 
aspect are changing authorization requirements in development or
even after taking the application into production.  Then, privileges of
certain roles need to be easily adjusted when the original assumptions
concerning access control prove unrealistic.  In these situations, a
declarative approach as offered by this plugin increases the development
and maintenance efficiency.

Plugin features
* Authorization at controller action level
* Authorization helpers for Views
* Authorization at model level
  * Authorize CRUD (Create, Read, Update, Delete) activities
  * Query rewriting to automatically only fetch authorized records
* DSL for specifying Authorization rules in an authorization configuration

* An authentication mechanism 
  * User object in Controller#current_user
* User object needs to respond to a method :roles, which should return an 
  array of role symbols
See below for installation instructions.

= Authorization Data Model

 ----- App domain ----|-------- Authorization conf ---------|------- App domain ------

                       includes                   includes
                        .--.                        .---.
                        |  v                        |   v
  .------.  can_play  .------.  has_permission  .------------.  requires  .----------.
  | User |----------->| Role |----------------->| Permission |<-----------| Activity |
  '------' *        * '------' *              * '------------' 1        * '----------'
                                           1 /        | 1     \ *
                                 .-----------.   .---------.  .-----------.
                                 | Privilege |   | Context |  | Attribute |
                                 '-----------'   '---------'  '-----------'

In the application domain, each *User* may be assigned to *Roles* that should 
define the users' job in the application, such as _Administrator_.  On the 
right-hand side of this diagram, application developers specify which *Permissions* 
are necessary for users to perform activities, such as calling a controller action,
viewing parts of a View or acting on records in the database.  Note that
Permissions consist of an *Privilege* that is to be performed, such as _read_, 
and a *Context* in that the Operation takes place, such as _companies_.

In the authorization configuration, Permissions are assigned to Roles and Role
and Permission hierarchies are defined.  *Attributes* may be employed to allow
authorization according to dynamic information about the context and the
current user, e.g. "only allow access on employees that belong to the
current user's branch."

= Examples

== Controller

If authentication is in place, enabling user-specific access control may be
as simple as one call to filter_access_to :all which simply requires the 
according privileges for present actions.  E.g. the privilege index_users is
required for action index.  This works as a first default configuration
for RESTful controllers, with these privileges easily handled in the
authorization configuration, which will be described below.

    class EmployeeController < ApplicationController
      filter_access_to :all
      def index

When custom actions are added to such a controller, it helps to define more
clearly which privileges are the respective requirements.  That is when the
filter_access_to call may become more verbose:

    class EmployeeController < ApplicationController
      filter_access_to :all
      # this one would be included in :all, but :read seems to be
      # a more suitable privilege than :auto_complete_for_user_name
      filter_access_to :auto_complete_for_employee_name, :require => :read
      def auto_complete_for_employee_name

For some actions it might be necessary to check certain attributes of the
object the action is to be acting on.  Then, the object needs to be loaded 
before the action's access control is evaluated.  On the other hand, some actions
might prefer the authorization to ignore specific attribute checks as the object is
unknown at checking time, so attribute checks and thus automatic loading of
objects needs to be enabled explicitly.

    class EmployeeController < ApplicationController
      filter_access_to :update, :attribute_check => true
      def update
        # @employee is already loaded from param[:id]
        @employee ||= Employee.find(param[:id])

If the access is denied, a +permission_denied+ method is called on the
current_controller, if defined and the issue is logged.
For further customization of the filters and object loading, have a look at 
the complete API documentation of filter_access_to in 

== Views

In views, a simple permitted_to? helper makes showing blocks according to the
current user's privileges easy:

    <% permitted_to?(:create, :employees) do %>
    <%= link_to 'New', new_employee_path %>
    <% end %>
    <% for employee in @employees %>
    <%= link_to 'Edit', edit_employee_path(company) if permitted_to?(:update, employee) %>
    <% end %>

See also Authorization::AuthorizationHelper.

== Models

There are two destinct features for model security built into this plugin:
authorizing CRUD operations on objects as well as query rewriting to limit
results according to certain privileges.

See also Authorization::AuthorizationInModel.

=== Model security for CRUD opterations
To activate model security, all it takes is an explicit enabling for each
model that model security should be enforced on, i.e.

    class Employee < ActiveRecord::Base

fails, if the current user is not allowed to :create :employees according
to the authorization rules.  For the application to find out about what 
happened if an operation is denied, the filters throw 
Authorization::NotAuthorized exceptions.

As access control on read are costly, with possibly lots of objects being
loaded at a time in one query, checks on read need to be actived explicitly by
adding the :include_read option.

=== Query rewriting using named scopes
When retrieving large sets of records from databases, any authorization needs
to be integrated into the query in order to prevent inefficient filtering
afterwards and to use LIMIT and OFFSET in SQL statements.  To keep authorization
rules out of the source code, this plugin offers query rewriting mechanisms
through named scopes.  Thus,


returns all employee records that the current user is authorized to read.  In
addition, just like normal named scopes, query rewriting may be chained with
the usual find method:

    Employee.with_permissions_to(:read).find(:all, :conditions => ...)

If the current user is completely missing the permissions, an 
Authorization::NotAuthorized exception is raised.  Through 
Model.obligation_conditions, application developers may retrieve
the conditions for manual rewrites.

== Authorization Rules

Authorization rules are defined in config/authorization_rules.rb.  E.g.

    authorization do
      role :admin do
        has_permission_on :employees, :to => [:create, :read, :update, :delete]

There is a default role :+guest+ that is used if a request is not associated
with any user or with a user without any roles.  So, if your application has
public pages, :+guest+ can be used to allow access for users that are not
logged in.  All other roles are application defined and need to be associated
with users by the application.

Privileges, such as :create, may be put into hierarchies to simplify
maintenance.  So the example above has the same meaning as

    authorization do
      role :admin do
        has_permission_on :employees, :to => :manage

    privileges do
      privilege :manage do
        includes :create, :read, :update, :delete

Privilege hierarchies may be context-specific, e.g. applicable to :employees.

    privileges do
      privilege :manage, :employees, :includes => :increase_salary

For more complex use cases, authorizations need to be based on attributes.  E.g.
if a branch admin should manage only employees of his branch:

    authorization do
      role :branch_admin do
        has_permission.on :employees do
          to :manage
          # user refers to the current_user when evaluating
          if_attribute :branch => is {user.branch}

Lastly, not only privileges may be organized in a hierarchy but roles as well.
Here, project manager inherit the permissions of employees.

      role :project_manager do
        includes :employee

See also Authorization::Reader.

= Installation of declarative_authorization and Usage

To install simply execute in your applications root directory
  cd vendor/plugins && git clone git://

* provide the requirements as noted below, 
* create a basic config/authorization_rules.rb--you might want to take the 
  provided example authorization_rules.dist.rb in the plugin root as a starting 
* add +filter_access_to+, +permitted_to+? and model security as needed.

== Providing the Plugin's Requirements
The requirements are
* An authentication mechanism 
* A user object returned by controller.current_user
* An array of role symbols returned by user.roles

Of the various ways to provide these requirements, here is one way employing

* Install restful_authentication
   cd vendor/plugins && git clone git:// restful_authentication
   ruby script/generate authenticated user sessions
* Move "include AuthenticatedSystem" to ApplicationController
* Add +before_filter+ :+login_required+ to controllers where a user should be
  forced to log in;  if parts of your application are public, 
  +filter_access_to+ calls as described above are sufficient.
* If you'd like to use model security, add a before_filter that sets the user 
  globally to your ApplicationController.  Note, this is by no means thread-safe.
   before_filter :set_current_user
   def set_current_user
     Authorization.current_user = current_user

* Add roles field to User model: a migration and table for roles,
  +has_many+ :+roles+ in User model and a roles method that returns the roles 
  as an Array of Symbols, e.g.
   def roles
     (super || []).map {|r| r.title.to_sym}

== Debugging Authorization

Currently, the main means of debugging authorization decisions is logging and
exceptions.  Denied access to actions is logged to +warn+ or +info+, including
some hints about what went wrong.

All bang methods throw exceptions which may be used to retrieve more
information about a denied access than a Boolean value.

== Contact

Steffen Bartsch
TZI, Universität Bremen, Germany
sbartsch at

== Licence

Copyright (c) 2008 Steffen Bartsch, TZI, Universität Bremen, Germany
released under the MIT license

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