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Access Control Mechanisms

You can control access in several way with Windows Communication Foundation (WCF). This topic briefly discusses the various mechanisms and provides suggestions on when to use each; it is intended to help you select the correct mechanism to use. The access technologies are listed in order of complexity. The simplest is the PrincipalPermissionAttribute; the most complex is the Identity Model.

In addition to these mechanisms, impersonation and delegation with WCF is explained in Delegation and Impersonation with WCF.

The PrincipalPermissionAttribute is used to restrict access to a service method. When the attribute is applied to a method, it can be used to demand a specific caller's identity or membership in a Windows group or ASP.NET role. If the client is authenticated using an X.509 certificate, it is given a primary identity that consists of the subject name plus the thumbprint of the certificate.

Use the PrincipalPermissionAttribute to control access to resources on the computer that the service is running on, and if the users of the service will always be part of the same Windows domain that the service is running on. You can easily create Windows groups that have specified levels of access (such as none, read-only, or read and write).

For more information about using the attribute, see How to: Restrict Access with the PrincipalPermissionAttribute Class. For more information about identity, see Service Identity and Authentication.

A feature of ASP.NET is the membership provider. Even though the membership provider is not technically an access control mechanism, it allows controlling access to the service by limiting the set of possible identities that can access the service's endpoint. The membership feature includes a database that can be populated with user name/password combinations that enable users of a Web site to establish accounts with the site. To access a service that uses the membership provider, a user must log on with his or her user name and password.

Note Note

You must first populate the database using the ASP.NET feature before a WCF service can use it for authorization purposes.

You can also use the membership feature if you already have a membership database from an existing ASP.NET Web site and you want to enable the same users to use your service, authorized with the same user names and passwords.

For more information about using the membership feature in a WCF service, see How to: Use the ASP.NET Membership Provider.

Another feature of ASP.NET is the ability to manage authorization using roles. The ASP.NET role provider enables a developer to create roles for users and to assign each user to a role or roles. As with the membership provider, the roles and assignments are stored in a database, and can be populated using tools provided by a particular implementation of the ASP.NET role provider. As with the membership feature, WCF developers can use the information in the database to authorize service users by roles. They can, for example, use the role provider in combination with the PrincipalPermissionAttribute access control mechanism described above.

You can also use the ASP.NET role provider if you have an existing ASP.NET role provider database and want to use the same set of rules and user assignments in your WCF service.

For more information about using the role provider feature, see How to: Use the ASP.NET Role Provider with a Service.

Another feature combines the Authorization Manager (AzMan) with the ASP.NET role provider to authorize clients. When ASP.NET hosts a Web service, AzMan can be integrated into the application so that authorization to the service is done through AzMan. ASP.NET role manager provides an API that enables you to manage application roles, add and remove users from roles, and check role membership, but it does not allow you to query whether a user is authorized to perform a named task or operation. AzMan allows you to define individual operations and combine them into tasks. With AZMan, in addition to role checks, you can also check whether a user can perform a task. Role assignment and task authorization can be configured outside of the application or performed programmatically within the application. The AzMan administration Microsoft Management Console (MMC) snap-in allows administrators to change the tasks a role can perform at run time and to manage each user's membership of roles.

You can also use AzMan and the ASP.NET role provider if you already have access to an existing AzMan installation and want to authorize your service users using the features of the AzMan/role provider combination.

For more information about AzMan and the ASP.NET role provider, see How To: Use Authorization Manager (AzMan) with ASP.NET 2.0. For more information about using AzMan and the role provider for WCF services, see How to: Use the ASP.NET Authorization Manager Role Provider with a Service.

The Identity Model is a set of APIs that enable you to manage claims and policies to authorize clients. With the Identity Model, you can examine every claim contained in credentials that the caller used to authenticate itself to the service, compare the claims to the set of policies for the service, and grant or deny access based on the comparison.

Use the Identity Model if you need fine control and the ability to set specific criteria before granting access. For example, when using the PrincipalPermissionAttribute, the criterion is simply that the identity of the user is authenticated and belongs to a specific role. In contrast, using the Identity Model, you can create a policy that states the user must be over 18 years of age and possesses a valid driver's license before being allowed to view a document.

One example where you can benefit from the Identity Model claim-based access control is when using federation credentials in the issued token scenario. For more information about federation and issued tokens, see Federation and Issued Tokens.

For more information about the Identity Model, see Managing Claims and Authorization with the Identity Model.

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