Professional ASP.NET 3.5 in C# and Visual Basic Part 108 pdf

Evjen c21.tex V2 - 01/28/2008 3:15pm Page 1028 Chapter 21: Security are configured. Highlight .aspx in the list of mappings and click the Edit button. Figure 21-16 shows the result. In the Executable text box, you can see that all .aspx pages map to the aspnet_isapi.dll from ASP.NET, and that you can also specify which types of requests are allowed in the application. You can allow either all verbs (for example, GET or POST ) or you can specify which verbs are allowed access to the application. One important point regarding these mappings is that you do not see .html , .htm , .jpg ,orotherfile extensions such as .txt in the list. Your application will not be passing requests for these files to ASP .NET. That might not be a big deal, but in working through the various security examples in this chapter, you might want to have the same type of security measures applied to these files as to .aspx pages. If, for instance, you want all .html pages to be included in the forms authentication model that you require for your ASP.NET application, you must add .html (or whatever file extension you want) to the list. To do so, click the Add button in the Application Configuration dialog. In the next dialog, you can add the ASP.NET DLL to the Executable text box, and the appropriate file extension and verbs to the list before adding the mapping to your application’s mapping table. This example is illustrated in Figure 21-17. Figure 21-17 When dealing with the security of your site, you have to remember all the files that might not be included in the default mapping list and add the ones you think should fall under the same security structure. If you are working with Windows Vista, you can get to the same functionality through the IIS Manager. In this tool, select Handler Mappings in the IIS section. You will find a large list of mappings that have already been provided. This is illustrated in Figure 21-18. By highlighting the *.aspx option and pressing the Edit button, you see that this extension is mapped to %windir% \ Microsoft.NET \ Framework \ v2.0.50727 \ aspnet_isapi.dll , as shown in Figure 21-19. Pressing the Request Restrictions button provides a dialog that enables you to select the verbs allowed (as shown in Figure 21-20). 1028 Evjen c21.tex V2 - 01/28/2008 3:15pm Page 1029 Chapter 21: Security Figure 21-18 Figure 21-19 1029 Evjen c21.tex V2 - 01/28/2008 3:15pm Page 1030 Chapter 21: Security Figure 21-20 Figure 21-21 1030 Evjen c21.tex V2 - 01/28/2008 3:15pm Page 1031 Chapter 21: Security Using the ASP.NET MMC Snap-In The ASP.NET MMC console (covered in more detail in Chapter 34) enables you to edit the web.config and machine.config files using an easy-to-use GUI instead of having to dig through the text of those files yourself to make the necessary changes. This option is only available in either Windows Server 2003 or Windows XP. Most of the items examined in this book can also be modified and changed using this dialog. The plug-in is available on the ASP.NET tab (see Figure 21-21) of your Web application running under IIS. When you make the changes directly in the dialog, you are also making the hardcoded changes to the actual configuration files. Click the Edit Configuration button on the ASP.NET tab, and the ASP.NET Configuration Settings dialog opens. There you can modify how your forms authentication model works in the GUI without going to the application’s web.config file directly. Figure 21-22 shows an example of working with forms authentication in the GUI. Figure 21-22 1031 Evjen c21.tex V2 - 01/28/2008 3:15pm Page 1032 Chapter 21: Security Using the IIS 7.0 Manager You will not find the ASP.NET MMC Snap In within Windows Vista. Instead, you will be able to make all the same site modifications through the Internet Information Services (IIS) Manager (as shown in Figure 21-23). Figure 21-23 After making any changes through this dialog, you can select the Apply Changes link in the Actions pane and it will notify you if t he changes made have been saved. When successful, the changes made a re applied to the site’s web.config file. Summary This chapter covered some of the foundation items of ASP.NET security and showed you how to apply both authentication and authorization to your Web applications. It reviewed some of the various authen- tication and authorization models at your disposal, such as Basic, Digest, and Windows Integrated Authentication. Other topics included forms-based authentication and how to construct your own forms-based authentication models outside of the ones provided via ASP.NET 3.5 by using the member- ship and role management capabilities it provides. The chapter also discussed how to use authentication properties within your applications and how to authorize users and groups based on those properties. 1032 Evjen c22.tex V2 - 01/28/2008 3:19pm Page 1033 State Management Why is state management such a difficult problem that it requires an entire chapter in a book on programming? In the old days (about 15 years ago), using standard client-server architecture meant using a fat client and a fat server. Perhaps your Visual Basic 6 application could talk to a database. The state was held either on the client-side or in the server-side database. Typically, you could count on a client having a little bit of memory and a hard drive of its own to manage state. The most important aspect of traditional client/server design, however, was that the client was always connected to the server. It’s easy to forget, but HTTP is a stateless protocol. For the most part, a connection is built up and torn down each time a call is made to a remote server. Yes, HTTP 1.1 includes a keep-alive technique that provides optimizations at the TCP level. Even with these optimizations, the server has no way to determine that subsequent connections came from the same client. Although the Web has the richness of DHTML and Ajax, JavaScript, and HTML 4.0 on the client side, the average high-powered Intel Core Duo with a few gigabytes of RAM is still being used only to render HTML. It’s quite ironic that such powerful computers on the client side are still so vastly underutilized when it comes to storing state. Additionally, although many individuals have broadband, it is not universally used. Developers must still respect and pay attention to the dial-up users of the world. When was the last time that your project manager told you that bandwidth was not an issue for your Web application? The ASP.NET concept of a Session that is maintained over the statelessness of HTTP is not a new one, and it existed before ASP.NET and even before classic ASP. It is, however, a very effective and elegant way to maintain state. There are, however, a number of different choices available to you, of which the ASP.NET session is just one. There have been a few subtle changes between ASP.NET 1.x and 2.0/3.5 that will be covered in this chapter. The Session objectremainsasbefore,butthe option to plug in your own session state provider is now available. Evjen c22.tex V2 - 01/28/2008 3:19pm Page 1034 Chapter 22: State Management What Are Your Choices? Given a relatively weak client, a stateless protocol such as HTTP, and ASP.NET on the server side, how do you manage state on the Web? Figure 22-1 is a generalized diagram that identifies the primary means available for managing state. The problem is huge, and the solution range is even larger. This chapter assumes that you are not using Java applets or ActiveX controls to manage state. Although these options are certainly valid (although complex) solutions to the state problem, they are beyond the scope of this book. Session Application ASP.Net worker process Web server Hidden HTML form field and/or JavaScript array Cookies (HTTP headers) http:// /page.aspx?state=some State in the URL Client Browser Cache OOP session state Figure 22-1 If you remember one thing about state management, remember this: There is no right answer. Some answers are more right than others, certainly; but there are many, many ways to manage state. Think about your last project. How many days were spent trying to decide where you should manage state? The trick is to truly understand the pros and cons of each method. To make an educated decision about a method, you should understand the lifecycle of a request and the opportunities for state management at each point in the process: 1. A Web browser makes an HTTP GET request for a page on your server, http://myserver/ myapp/mypage.aspx . This client Web b rowser has never visited your site before. 2. IIS and your ASP.NET application respond by returning HTML rendered by mypage.aspx . Additionally mypage.aspx returns a cookie with a unique ID to track this Web browser. Remember that a cookie is actually a slightly abstract concept. The cookie is set by return- ing a Set-Cookie HTTP Header to the client. The client then promises to return the values of the cookie in every subsequent HTTP call in the HTTP header. The state in this example is actually an agreement between the client and server to bounce the cookie back-and-forth on every request in response. 3. The HTML that is returned may contain hidden text boxes such as < input type="hidden" value="somestate"/ >. These text boxes are similar to cookies because they are passed back to the server if the form on this page is submitted. Cookies are set per domain; hidden form fields are set per page. 1034 Evjen c22.tex V2 - 01/28/2008 3:19pm Page 1035 Chapter 22: State Management 4. Upon the next request, the previously set cookies are returned to the server. If this request was the submission of the form as an HTTP POST, all fields in the Form are returned — hidden or otherwise. 5. The unique identifier that was set earlier as a cookie can now be used as a key into any kind of server-side state mechanism. That state might be as simple as an in-memory hashtable, or as complicated as a SQL database. One of the repeating themes you might notice is the agreement between the client and the server to pass information back and forth. That information can be in the URL, in HTTP headers, or even in the submitted Form as an input field. On the server side, you have a few options. You’ll want to weigh the options based on the amount of memory you have available, the amount of data you want to store, and how often you’ll require access to the data. The following tables express each of the server-side and client-side options and list a few pros and cons for each. Server-Side Option Pros Cons Application State Fast. Shared among all users. State is stored once per server in multiple server configurations. Cache Object (Application Scope) Like the Application State but includes expiration via Dependencies (see Chapter 23 on caching). State is stored once per server in multiple server configurations. Session State Three choices: in process, out of process, DB-backed. Can be configured as cookieless. Can be abused. You pay a serialization cost when objects leave the process. In process requires Web Server affinity. Cookieless configuration makes it easier to hijack. Database State can be accessed by any server in a Web farm. Pay a serialization and persistence cost when objects leave the process. Requires a SQL Server license. On the client side, every available option costs you in bandwidth. Each option involves passing data back and forth from client to server. Every byte of data you store will be paid for twice: once when it is passed to the server and once when it is passed back. Client-Side Option Pros Cons Cookie Simple Can be rejected by browser. Not appropriate for large amounts of data. Inappropriate for sensitive data. Size cost is paid on every HTTP Request and Response. Hidden Field Simple for page-scoped data Not appropriate for large amounts of data. Inappropriate for sensitive data. 1035 Evjen c22.tex V2 - 01/28/2008 3:19pm Page 1036 Chapter 22: State Management Client-Side Option Pros Cons ViewState Simple for page-scoped data Encoding of serialized object as binary Base64-encoded data adds approximately 30 percent overhead. Small serialization cost. Has a negative reputation, particularly with DataGrids. ControlState Simple for page-scoped control-specific data Like ViewState, but used for controls that require ViewState even if the developer has turned it off. QueryString (URL) Incredibly simple and often convenient if you want your URLs to be modified directly by the end user Comparatively complex.Can’tholdalotof information. Inappropriate for sensitive data. Easily modified by the end user. These tables provided you with some of the server-side and client-side options. The improvements to caching in ASP.NET 2.0/3.5 are covered in Chapter 23. Understanding the Session Object in ASP.NET In classic ASP, the Session object was held in-process (as was everything) to the IIS process. The user received a cookie with a unique key in the form of a GUID. The Session key was an inde x into a dictionary where object references could be stored. In all versions of ASP.NET the Session object offers an in-process option, but also includes an out-of- process and database-backed option. Additionally, the developer has the option to enable cookieless session state where the Session key appears in the URL rather than being sent as a cookie. Sessions and the Event Model The HttpApplication object raises a series of events during the life of the HTTP protocol request: ❑ BeginRequest : This event fires at the b eginning of every request. ❑ AuthenticateRequest : This event is used by the security module a nd indicates that a request is about to be authenticated. This is where the security module, or you, determines who the user is. ❑ AuthorizeRequest : This event is used by the security module and indicates that a request is about to be authorized. This is where the security module, or you, determines what the user is allowed to do. ❑ ResolveRequestCache : This event is used by the caching module to determine whether this now-authorized request can bypass any additional processing. ❑ AcquireRequestState : This event indicates that all session state associated with this HTTP request is about to be acquired. 1036 Evjen c22.tex V2 - 01/28/2008 3:19pm Page 1037 Chapter 22: State Management Session state is available to you, t he developer, after the AcquireRequestState event fires. The session state key that is unique to each user is retrieved either from a cookie or from the URL. ❑ PreRequestHandlerExecute : This is the last event you get before the HttpHandler class for this request is called. Your application code, usually in the form of a Page, executes at this point in the process. ❑ PostRequestHandlerExecute : This is the event that fires just after the HttpHandler is called. ❑ ReleaseRequestState : Indicates that the session state should be stored. Session state is persisted at this point, using whatever Session-state module is configured in web.config . ❑ UpdateRequestCache : All work is complete, and the resulting output is ready to be added to the cache. ❑ EndRequest : This is the last event called during a request. You can see from the preceding list that AcquireRequestState and ReleaseRequestState are two significant events in the life of the Session object. By the time your application code executes, the Session object has been populated using the Session key that was present in the cookie, or as you see later, from the URL. If you want to handle some processing at the time the Session begins, rather than handling it in AcquireRequestState , you can define an event handler for the Start event of a SessionState HttpModule. Sub Session_OnStart() ’this fires after session state has been acquired by the SessionStateModule. End Sub The Session object includes both Start and End events that you can hook event handlers to for your own needs. However, the Session_OnEnd event is supported only in the In-Process Session State mode. This event will not be raised if you use out-of-process State Server or SQL Server modes. The Session ends, but your handlers will never hear about it. Pre- and post-events occur at almost every point within the life of an HTTP request. Session state can be manipulated at any point after AcquireRequestState , including in the Global.asax within the Session_OnStart event. The HttpSessionState object can be used within any event in a subclass of the Page object. Because the pages you create in ASP.NET derive from System.Web.UI.Page , you can access Session State as a collection because System.Web.SessionState.HttpSessionState implements ICollection . 1037 . server-side and client-side options. The improvements to caching in ASP. NET 2.0 /3. 5 are covered in Chapter 23. Understanding the Session Object in ASP. NET In classic ASP, the Session object was held in- process. 01/28/2008 3: 15pm Page 1 030 Chapter 21: Security Figure 21-20 Figure 21-21 1 030 Evjen c21.tex V2 - 01/28/2008 3: 15pm Page 1 031 Chapter 21: Security Using the ASP. NET MMC Snap -In The ASP. NET MMC. available in either Windows Server 20 03 or Windows XP. Most of the items examined in this book can also be modified and changed using this dialog. The plug -in is available on the ASP. NET tab (see