Securing WCF Data Services
This topic describes security considerations that are specific to developing, deploying, and running WCF Data Services and applications that access services that support the Open Data Protocol (OData). You should also follow recommendations for creating secure .NET Framework applications.
When planning how to secure a WCF Data Services-based OData service, you must address both authentication, the process of discovering and verifying the identity of a principal, and authorization, the process of determining whether an authenticated principal is allowed to access the requested resources. You should also consider whether to encrypt the message by using SSL.
Authenticating Client Requests
WCF Data Services does not implement any kind of authentication of its own, but rather relies on the authentication provisions of the data service host. This means that the service assumes that any request that it receives has already been authenticated by the network host and that the host has correctly identified the principle for the request appropriately via the interfaces provided by WCF Data Services. These authentication options and approaches are detailed in OData and Authentication series.
Authentication Options for a WCF Data Service
The following table lists some of the authentication mechanisms that are available to help you authenticate requests to a WCF Data Service.
|Anonymous authentication||When HTTP anonymous authentication is enabled, any principle is able to connect to the data service. Credentials are not required for anonymous access. Use this option only when you want to allow anyone to access the data service.|
|Basic and digest authentication||Credentials consisting of a user name and password are required for authentication. Supports authentication of non-Windows clients. Security Note: Basic authentication credentials (user name and password) are sent in the clear and can be intercepted. Digest authentication sends a hash based-on the supplied credentials, which makes it more secure than basic authentication. Both are susceptible to man-in-the-middle attacks. When using these authentication methods, you should consider encrypting communication between client and the data service by using the Secure Sockets Layer (SSL).
Microsoft Internet Information Services (IIS) provides an implementation of both basic and digest authentication for HTTP requests in an ASP.NET application. This Windows Authentication Provider implementation enables a .NET Framework client application to supply credentials in the HTTP header of the request to the data service to seamlessly negotiate authentication of a Windows user. For more information, see Digest Authentication Technical Reference.
When you want to have your data service use basic authentication based on some custom authentication service and not Windows credentials, you must implement a custom ASP.NET HTTP Module for authentication.
For an example of how to use a custom basic authentication scheme with WCF Data Services, see the post on Custom Basic Authentication in the OData and authentication series.
|Windows authentication||Windows-based credentials are exchanged by using NTLM or Kerberos. This mechanism is more secure than basic or digest authentication, but it requires that the client be a Windows-based application. IIS also provides an implementation of Windows authentication for HTTP requests in an ASP.NET application. For more information, see ASP.NET Forms Authentication Overview.
For an example of how to use Windows authentication with WCF Data Services, see the post on Windows Authentication in the OData and authentication series.
|ASP.NET forms authentication||Forms authentication lets you authenticate users by using your own code and then maintain an authentication token in a cookie or in the page URL. You authenticate the user name and password of your users using a login form that you create. Unauthenticated requests are redirected to a login page, where the user provides credentials and submits the form. If the application authenticates the request, the system issues a ticket that contains a key for reestablishing the identity for subsequent requests. For more information, see Forms Authentication Provider. Security Note: By default, the cookie that contains the forms authentication ticket is not secured when you use forms authentication in a ASP.NET Web application. You should consider requiring SSL to protect both the authentication ticket and the initial login credentials.
For an example of how to use forms authentication with WCF Data Services, see the post on Forms Authentication in the OData and authentication series.
|Claims-based authentication||In claims-based authentication, the data service relies on a trusted "third-party" identity provider service to authenticate the user. The identity provider positively authenticates the user that is requesting access to data service resources and issues a token that grants access to the requested resources. This token is then presented to the data service, which then grants access to the user based on the trust relationship with the identity service that issued the access token.
The benefit of using a claims-based authentication provider is that they can be used to authenticate various types of clients across trust domains. By employing such a third-party provider, a data service can offload the requirements of maintaining and authenticating users. OAuth 2.0 is a claims-based authentication protocol that is supported by Windows Azure AppFabric Access Control for federated authorization as a service. This protocol supports REST-based services. For an example of how to use OAuth 2.0 with WCF Data Services, see the post on OData and OAuth in the OData and authentication series.
Authentication in the Client Library
By default, the WCF Data Services client library does not supply credentials when making a request to an OData service. When login credentials are required by the data service to authenticate a user, these credentials can be supplied in a NetworkCredential accessed from the Credentials property of the DataServiceContext, as in the following example:
// Set the client authentication credentials. context.Credentials = new NetworkCredential(userName, password, domain);
' Set the client authentication credentials. context.Credentials = _ New NetworkCredential(userName, password, domain)
For more information, see How to: Specify Client Credentials for a Data Service Request.
When the data service requires login credentials that cannot be specified by using a NetworkCredential object, such as a claims-based token or cookie, you must manually set headers in the HTTP request, usually the
Cookie headers. For more information about this kind of authentication scenario, see the post OData and Authentication: Client-Side Hooks. For an example of how to set HTTP headers in a request message, see How to: Set Headers in the Client Request.
Generally, the data service accesses required resources, such as files on the server or a database, by using the credentials of the worker process that is hosting the data service. When using impersonation, ASP.NET applications can execute with the Windows identity (user account) of the user making the request. Impersonation is commonly used in applications that rely on IIS to authenticate the user, and the credentials of this principle are used to access the required resources. For more information, see ASP.NET Impersonation.
Configuring Data Service Authorization
Authorization is the granting of access to application resources to a principle or process that is identified based on a previously successful authentication. As a general practice, you should only grant sufficient rights to users of the data service to perform the operations required by client applications.
Restrict Access to Data Service Resources
By default, WCF Data Services enables you to grant common read and write access against data service resources (entity set and service operations) to any user that is able to access the data service. Rules that define read and write access can be defined separately for each entity set exposed by the data service, as well as to any service operations. We recommend limiting both read and write access to only the resources required by the client application. For more information, see Minimum Resource Access Requirements.
Implement Role-Based Interceptors
Interceptors enable you to intercept requests against data service resources before they are acted on by the data service. For more information, see Interceptors. Interceptors enable you to make authorization decisions based the authenticated user that is making the request. For an example of how to restrict access to data service resources based on an authenticated user identity, see How to: Intercept Data Service Messages.
Restrict Access to the Persisted Data Store and Local Resources
The accounts that are used to access the persisted store should be granted only enough rights in a database or the file system to support the requirements of the data service. When anonymous authentication is used, this is the account used to run the hosting application. For more information, see How to: Develop a WCF Data Service Running on IIS. When impersonation is used, authenticated users must be granted access to these resources, usually as part of a Windows group.
Other Security Considerations
Secure the Data in the Payload
OData is based on the HTTP protocol. In an HTTP message, the header may contain valuable user credentials, depending on the authentication implemented by the data service. The message body may also contain valuable customer data that must be protected. In both of these cases, we recommend that you use SSL to protect this information over the wire.
Ignored Message Headers and Cookies
HTTP request headers, other than those that declare content types and resource locations, are ignored and are never set by the data service.
Cookies can be used as part of an authentication scheme, such as with ASP.NET Forms Authentication. However, any HTTP cookies set on an incoming request are ignored by WCF Data Services. The host of a data service may process the cookie, but the WCF Data Services runtime never analyzes or returns cookies. The WCF Data Services client library also does not process cookies sent in the response.
Custom Hosting Requirements
By default, WCF Data Services is created as an ASP.NET application hosted in IIS. This enables the data service to leverage the secure behaviors of this platform. You can define WCF Data Services that are hosted by a custom host. For more information, see Hosting the Data Service. The components and platform hosting a data service must ensure the following security behaviors to prevent attacks on the data service:
Limit the length of the URI accepted in a data service request for all possible operations.
Limit the size of both incoming and outgoing HTTP messages.
Limit the total number of outstanding requests at any given time.
Limit the size of HTTP headers and their values, and provide WCF Data Services access to header data.
Detect and counter known attacks, such as TCP SYN and message replay attacks.
Values Are Not Further Encoded
Property values sent to the data service are not further encoded by the WCF Data Services runtime. For example, when a string property of an entity contains formatted HTML content, the tags are not HTML encoded by the data service. The data service also does not further encode property values in the response. The client library also does not perform any additional encoding.
Considerations for Client Applications
The following security considerations apply to applications that use the WCF Data Services client to access OData services:
The client library assumes that the protocols used to access the data service provide an appropriate level of security.
The client library uses all the default values for timeouts and parsing options of the underlying platform-provided transport stacks.
The client library does not read any settings from application configuration files.
The client library does not implement any cross domain access mechanisms. Instead, it relies on the mechanisms provided by the underlying HTTP stack.
The client library has no user interface elements, and it never tries to display or render the data that it receives or sends.
We recommend that client applications always validate user input as well as data accepted from untrusted services.
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