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1.1 Conceptual Overview

Authorization is the process of controlling access to resources. Once authentication has been accomplished, the next task is to decide whether a particular request is authorized. Management of network systems often models broad authorization decisions through roles, groups, and claims; for example, all engineers who have access to a specific printer, all sales personnel who have access to a certain web server, or confidential information where access is granted only to certain authorized user groups or users based on the claims configured. Making authorization information consistently available to a number of services allows for simpler management.

The authorization system always deals with two entities, the security principal (subject) and the resource (object) or business operation/task, as shown in the following diagram. When a security principal requests access to a resource or needs to perform a business operation/task that requires access, the authorization system checks all accesses that are requested by the security principal.

The following diagram shows a generic authorization model.


Figure 1: Generic authorization model

To perform the tasks that they are designed for, applications must carry out operations and access system resources on behalf of the application's user while protecting these operations and resources from unauthorized access. Administrators can control whether a process can access securable objects or perform various system administration tasks.

Windows was originally designed to meet the requirements of the C2 level of the Trusted Computer System Evaluation Criteria (TCSEC). The TCSEC program has since been supplanted by profiles that were written under the Common Criteria for Information Technology Security Evaluation specified in [CCITSE3.1-3], such as the Controlled Access Protection Profile (CAPP).

The C2 requirements (and later the CAPP requirements) for authorization are centered upon discretionary access control. For discretionary access control, the owner of a particular resource (or a delegate of the owner) determines the level of access others should have, which is in contrast to mandatory access control schemes in which another party maintains control over the resource regardless of the expectations of the owner.

This control was initially provided through the Discretionary Access Control (DAC) Model, which is an object-centric model using access control lists (ACLs). Each system object has an associated list of trustees (user account and group account) with specific sets of access rights for that object. This model lends itself well to securing access to well-defined, persistent resources, such as Active Directory, files, and the registry.

Windows Server 2003 operating system introduced a complementary authorization interface, called Authorization Manager (AzMan), which enables the role-based access control (RBAC) authorization model. Authorization Manager provides a natural framework for business process applications that require representing the organizational model within the application security framework.

In the DAC model, a resource manager (RM) manages its own set of objects, which are protected by a security descriptor. Whenever a client requests access to a resource protected by an RM, the RM makes a call to the authorization system to verify the authorization of the client's identity. In turn, the authorization system looks at the client security token, the requested access to the object, and the security descriptor on the object. The authorization system responds to the RM with "yes" or "no," enabling the RM to determine whether the client should be allowed to access the object.

In contrast to object-centric management, AzMan Role-Based Access Control (RBAC) provides a framework for developers to develop applications that are oriented around the notion of the role. Rather than managing access control on objects in the application, AzMan RBAC facilitates application development by providing a central object—a role—that a user is assigned to perform a particular job function within an application. A role directly implies authorization permissions on some defined set of resources.

Through the abstractions of the operation and task, AzMan RBAC permissions are typically granted through higher-level abstractions corresponding to high-level tasks defined by the application developer. Operations represent a single unit of application code, whereas tasks can be composed of multiple operations (and other tasks). Consider, for example, a web-based application that enables users to report project status, to publish status for viewing, and to view status. The COM development framework also has the notion of an application-specific role, which is very similar to the one used in the context of the AzMan RBAC model. The key difference with the AzMan RBAC is that the COM+ roles access control model can only be used in COM/COM+ applications, whereas the AzMan RBAC model can be integrated into any application type.

This section provides an overview of the following concepts, which are required to understand this document.

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