Returning Formal Data Structures in VB.NET

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Returning Formal Data Structures
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You can easily create a formal data structure to define the external interface of a web service by using a class. The data structure of the class will define the public interface of the web service, meaning that the web service interface is separate from the business object interface. The web service and this formal definition form a facade so that consumers of the web service don t know or care about the specific interface of the business object. For instance, you can define a class that describes the data for a project like this: Public Class ProjectData Private Private Private Private Private mId As Guid mName As String mStarted As String mEnded As String mDescription As String
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Public Property Id() As Guid Get Return mId End Get Set(ByVal value As Guid) mId = value End Set End Property ' remaining properties... End Class Then you can have the project-related web methods return a result of this type or even an array of results of this type. When this is returned as a result from a web method, its data will be
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CHAPTER 11 s WEB SERVICES INTERFACE
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converted into SOAP-formatted XML that s returned to the consumer. Figure 11-6 illustrates what I m talking about doing here.
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Figure 11-6. Using a facade to define the data returned to the consumer
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When consumers reference the web service, they will gain access to the definition of this type via the WSDL data that s associated with the service. This means that the consumer will have information about the data being returned in a very clear and concise format.
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s When creating a consumer for the web service, Visual Studio uses this information to create a proxy class Tip that mirrors the data structure. This gives consumer developers the benefits of IntelliSense, so that they can easily understand what data is required or returned from the web methods.
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The final consideration is authentication and security. Of course, there are many types and layers of security, but what I m focusing on here is how to use either CSLA .NET or Windows integrated security to identify the users and their roles. Even though the user in this case is a remote application, that application must still identify itself so that the business objects can apply their authorization rules. In short, a valid principal and identity object must be established to identify the calling application in some way. The remote consumer may use a hard-coded username and password, or prompt its actual user for credentials. What that application does is entirely its business, and really has nothing to do with the web service. All the web service can do is ensure that the consumer provides valid credentials so a principal and identity can be created. The business objects contain the authentication rules to do the rest. If you opt to use Windows integrated security, you ll need to configure IIS to disallow anonymous access to the virtual root containing the web service. You ll also add an <identity impersonate="true" /> element into the <system.web> section of the site s web.config file so that ASP.NET knows to impersonate the user account of the calling application. This will force the consumer to provide valid Windows credentials in order to interact with the web service.
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CHAPTER 11 s WEB SERVICES INTERFACE
No extra work is required in the web service or business object code, other than ensuring that the web.config file in the web service virtual root has the <appSettings> entry to configure CSLA .NET to use Windows security.
s Windows integrated security is probably not a viable option in most cases. It s relatively unlikely that Tip unknown clients on unknown platforms will be authenticated within your Windows domain. While the CSLA .NET architecture does support this option, using it would mean that consumers must start out with valid Windows domain accounts with which they can authenticate to your web server.
CSLA .NET security requires a bit more work, but avoids any necessity for the remote consumer (or its users) to have Windows domain user accounts in your environment. To implement CSLA .NET security, IIS should be left with the default configuration that allows anonymous users to access the virtual root. You must then include code in the web service to ensure that the calling code provides a username and password, which can be validated using the PTPrincipal class in the ProjectTracker.Library just like in the Windows Forms and Web Forms interfaces. The harder question is how to get the username and password from the consumer, and there are two basic approaches to an answer. The first of these is to have each web method include username and password parameters. Each time the consumer calls a web method, it would need to provide values for these two parameters (along with any other parameters the method requires). Within the web method, those two parameters could be passed to PTPrincipal.Login() to see if the credentials are valid. Although this can work, it pollutes the parameter lists of all the web methods. Each method ends up with these two extra parameters that really have nothing to do with the method itself. This is far from ideal. The other approach is to use the SOAP header to pass the information from consumer to server outside the context of the method, but as part of the same exchange of data. In other words, the username and password information will piggyback on the method call, but won t be part of the method call.
s Web Services Extensions (WSE) offers a more advanced implementation of this concept. WSE includes Tip the ability to encrypt the credentials over the network. In the future, Windows Communication Foundation (WCF or Indigo) will provide a similar advanced implementation. If you are going to pass credentials to web services, it is best to use one of these technologies that already provide the implementation.
This is a standard technique for passing extra information along with method calls. It s supported by the SOAP standard, and therefore by all SOAP-compliant client-development tools. What this means is that it s a perfectly acceptable approach in fact, it s the preferred approach. I ll use it in the sample interface in this chapter. One thing you need to keep in mind with this implementation is that the user s credentials are authenticated on every web service call. This could cause substantial load on your security database. Technologies such as WSE and WCF offer more advanced authentication options that may be more appropriate in many cases.
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