Professional ASP.NET 3.5 in C# and Visual Basic Part 106 ppt

Evjen c21.tex V2 - 01/28/2008 3:15pm Page 1008 Chapter 21: Security Attribute Description timeout Specifies the amount of time, in minutes, after which the cookie expires. The default value is 30 . cookieless Specifies whether the forms-based authentication process should use cookies when working with the authentication/authorization process. defaultUrl Specifies the default URL. domain Specifies the domain name to be sent with forms authentication cookies. slidingExpiration Specifies whether to apply a sliding expiration to the cookie. If set to True , the expiration of the cookie is reset with each request made to the server. The default value is False . enableCross AppsRedirect Specifies whether to allow for cross-application redirection. requireSSL Specifies whether a Secure Sockets Layer (SSL) connection is required when transmitting authentication information. After the web.config file is in place, t he next step is to create a typical page for your application that people can access. Listing 21-4 presents a simple page. Listing 21-4: A simple page — Default.aspx < %@ Page Language="VB" % > < html xmlns="http://www.w3.org/1999/xhtml" > < head runat="server" > < title > The Application < /title > < /head > < body > < form id="form1" runat="server" > < div > Hello World < /div > < /form > < /body > < /html > As you can see, this page simply writes Hello World to the browser. The real power of forms authentica- tion is shown in the Login.aspx page presented in Listing 21-5. Listing 21-5: The Login.aspx page VB < %@ Page Language="VB" % > < script runat="server" > Protected Sub Button1_Click(ByVal sender As Object, _ ByVal e As System.EventArgs) 1008 Evjen c21.tex V2 - 01/28/2008 3:15pm Page 1009 Chapter 21: Security If (TextBox1.Text = "BillEvjen" And TextBox2.Text = "Bubbles") Then FormsAuthentication.RedirectFromLoginPage(TextBox1.Text, True) Else Response.Write("Invalid credentials") End If End Sub < /script > < html xmlns="http://www.w3.org/1999/xhtml" > < head runat="server" > < title > Login Page < /title > < /head > < body > < form id="form1" runat="server" > < div > Username < br / > < asp:TextBox ID="TextBox1" runat="server" >< /asp:TextBox >< br / > < br / > Password < br / > < asp:TextBox ID="TextBox2" runat="server" TextMode="Password" >< /asp:TextBox >< br / > < br / > < asp:Button ID="Button1" OnClick="Button1_Click" runat="server" Text="Submit" / > < /div > < /form > < /body > < /html > C# < %@ Page Language="C#"% > < script runat="server" > protected void Button1_Click(object sender, EventArgs e) { if (TextBox1.Text == "BillEvjen" && TextBox2.Text == "Bubbles") { FormsAuthentication.RedirectFromLoginPage(TextBox1.Text, true); } else { Response.Write("Invalid credentials"); } } < /script > Login.aspx has two simple TextBox controls and a Button control that asks the user to submit his username and password. The Button1_Click event uses the RedirectFromLoginPage method of the FormsAuthentication class. This method does exactly what its name implies — it redirects the request from Login.aspx to the original requested resource. RedirectFromLoginPage takes two arguments. T he first is the name of the user, used for cookie authenti- cation purposes. This argument does not actually map to an account name and is used by ASP.NET’s URL authorization capabilities. The second argument specifies whether a durable cookie should be issued. If set to True , the end user does not need to log in again to the application from one browser session to the next. 1009 Evjen c21.tex V2 - 01/28/2008 3:15pm Page 1010 Chapter 21: Security Using the three pages you have constructed, each request for the Default.aspx page from Listing 21-4 causes ASP.NET to check that the proper authenticationtokenisinplace.Ifthepropertokenisnotfound, the request is directed to the specified login page (in this example, Login.aspx ). Looking at the URL in the browser, you can see that ASP.NET is using a querystring value to remember where to return the user after he has been authorized to proceed: http://localhost:35089/Security/Login.aspx?ReturnUrl=%2fSecurity%2fDefault.aspx Here, the querystring ReturnUrl is used with a value of the folder and page that was the initial request. Look more closely at the Login.aspx page from Listing 21-5, and note that the values placed in the two text boxes are checked to make sure they abide by a specific username and password. If they do , the RedirectFromLoginPage method is invoked; otherwise, the Response.Write() statement is used. In most cases, you do not want to hardcode a username and password in your code. Many other options exist for checking whether usernames and passwords come from authorized users. Some of the other options follow. Authenticating Against Values Contained in the web.config File The previous example is not the best approach for dealing with usernames and passwords offered for authentication. It is never a good idea to hardcode these things directly into your applications. Take a quick look at storing these values in the web.config file itself. The < forms > element in web.config that you worked with in Listing 21-3 can also take a sub-element. The sub-element, < credentials >, allows you to specify username and password combinations directly in the web.config file. You can choose from a couple of ways to add these values. The simplest method is shown in Listing 21-6. Listing 21-6: Modifying the web.config file to add username/password values < system.web > < authentication mode="Forms" > < forms name="Wrox" loginUrl="Login.aspx" path="/" > < credentials passwordFormat="Clear" > < user name="BillEvjen" password="Bubbles" / > < /credentials > < /forms > < /authentication > < authorization > < deny users="?" / > < /authorization > < /system.web > The < credentials > element has been included to add users and their passwords to the configuration file. < credentials > takes a single attribute — passwordFormat . The possible values of passwordFormat are Clear , MD5 ,and SHA1 . The following list describes each of these options: ❑ Clear : Passwords are stored in clear text. The user password is compared directly to this value without further transformation. ❑ MD5 : Passwords are stored using a Message Digest 5 (MD5) hash digest. When credentials are validated, the user password is hashed using the MD5 algorithm and compared for equality with 1010 Evjen c21.tex V2 - 01/28/2008 3:15pm Page 1011 Chapter 21: Security this value. The clear-text password is never stored or compared. This algorithm produces better performance than SHA1. ❑ SHA1 : Passwords are stored using the SHA1 hash digest. When credentials are validated, the user password is hashed using the SHA1 algorithm and compared for equality with this value. The clear-text password is never stored or compared. Use this algorithm for best security. In the example from Listing 21-6, you use a setting of Clear .Thisisnotthemostsecuremethod,butitis used for demonstration purposes. A sub-element of < credentials > is < user >; that is where you define the username and password for the authorized user with the attributes name and password . The next step is to change the Button1_Click event on the Login.aspx page shown earlier. This is illus- trated in Listing 21-7. Listing 21-7: Changing the Login.aspx page to work with the web.config file VB < %@ Page Language="VB" % > < script runat="server" > Protected Sub Button1_Click(ByVal sender As Object, _ ByVal e As System.EventArgs) If FormsAuthentication.Authenticate(TextBox1.Text, TextBox2.Text) Then FormsAuthentication.RedirectFromLoginPage(TextBox1.Text, True) Else Response.Write("Invalid credentials") End If End Sub < /script > C# < %@ Page Language="C#"% > < script runat="server" > protected void Button1_Click(object sender, EventArgs e) { if (FormsAuthentication.Authenticate(TextBox1.Text, TextBox2.Text)) { FormsAuthentication.RedirectFromLoginPage(TextBox1.Text, true); } else { Response.Write("Invalid credentials"); } } < /script > In this example, you simply use the Authenticate() method to get your ASP.NET page to look at the credentials stored in the web.config file for verification. The Authenticate() method takes two parameters — the username and the password that you are passing in to be checked. If the credential lookup is successful, the RedirectFromLoginPage method is invoked. It is best not to store your users’ passwords in the web.config file as clear text as the preceding example did. Instead, use one of the available hashing capabilities so you can keep the end user’s password out of 1011 Evjen c21.tex V2 - 01/28/2008 3:15pm Page 1012 Chapter 21: Security sight of prying eyes. To do this, simply store the hashed password in the configuration file as shown in Listing 21-8. Listing 21-8: Using encrypted passwords < forms name="Wrox" loginUrl="Login.aspx" path="/" > < credentials passwordFormat="SHA1" > < user name="BillEvjen" password="58356FB4CAC0B801F011B397F9DFF45ADB863892" / > < /credentials > < /forms > Using this kind of construct makes it impossible for even the developer to discover a password because the clear text password is never used. The Authenticate() method in the Login.aspx page hashes the password using SHA1 (because it is the method specified in the web.config ’s < credentials > node) and compares the two hashes for a match. If a match is found, the user is authorized to proceed. When using SHA1 or MD5, the only changes you make are in the web.config file and nowhere else. You do not have to make any changes to the login page or to any other page in the application. To store hashed passwords, however, you use the FormsAuthenticationHashPasswordForStoringInConfig- File method (probably the longest method name in the .NET Framework). You accomplish this in the following manner: FormsAuthentication.HashPasswordForStoringInConfigFile(TextBox2.Text, "SHA1") Authenticating Against Values in a Database Another common way to retrieve username/password combinations is by getting them directly from a datastore of some kind. This enables you, for example, to check the credentials input by a user against values stored in Microsoft’s SQL Server. The code for this is presented in Listing 21-9. Listing 21-9: Checking credentials in SQL Server (Login.aspx) VB < %@ Page Language="VB" % > < %@ Import Namespace="System.Data" % > < %@ Import Namespace="System.Data.SqlClient" % > < script runat="server" > Protected Sub Button1_Click(ByVal sender As Object, _ ByVal e As System.EventArgs) Dim conn As SqlConnection Dim cmd As SqlCommand Dim cmdString As String = "SELECT [Password] FROM [AccessTable] WHERE" & _ " (([Username] = @Username) AND ([Password] = @Password))" conn = New SqlConnection("Data Source=localhost;Initial " & _ "Catalog=Northwind;Persist Security Info=True;User ID=sa") cmd = New SqlCommand(cmdString, conn) cmd.Parameters.Add("@Username", SqlDbType.VarChar, 50) cmd.Parameters("@Username").Value = TextBox1.Text 1012 Evjen c21.tex V2 - 01/28/2008 3:15pm Page 1013 Chapter 21: Security cmd.Parameters.Add("@Password", SqlDbType.VarChar, 50) cmd.Parameters("@Password").Value = TextBox2.Text conn.Open() Dim myReader As SqlDataReader myReader = cmd.ExecuteReader(CommandBehavior.CloseConnection) If myReader.Read() Then FormsAuthentication.RedirectFromLoginPage(TextBox1.Text, False) Else Response.Write("Invalid credentials") End If myReader.Close() End Sub < /script > C# < %@ Page Language="C#"% > < %@ Import Namespace="System.Data" % > < %@ Import Namespace="System.Data.SqlClient" % > < script runat="server" > protected void Button1_Click(object sender, EventArgs e) { SqlConnection conn; SqlCommand cmd; string cmdString = "SELECT [Password] FROM [AccessTable] WHERE" + " (([Username] = @Username) AND ([Password] = @Password))"; conn = new SqlConnection("Data Source=localhost;Initial " + "Catalog=Northwind;Persist Security Info=True;User ID=sa"); cmd = new SqlCommand(cmdString, conn); cmd.Parameters.Add("@Username", SqlDbType.VarChar, 50); cmd.Parameters["@Username"].Value = TextBox1.Text; cmd.Parameters.Add("@Password", SqlDbType.VarChar, 50); cmd.Parameters["@Password"].Value = TextBox2.Text; conn.Open(); SqlDataReader myReader; myReader = cmd.ExecuteReader(CommandBehavior.CloseConnection); if (myReader.Read()) { FormsAuthentication.RedirectFromLoginPage(TextBox1.Text, false); } else { Response.Write("Invalid credentials"); } Continued 1013 Evjen c21.tex V2 - 01/28/2008 3:15pm Page 1014 Chapter 21: Security myReader.Close(); } < /script > Leave everything e lse from the previous examples the same, except for the Login.aspx page. You can now authenticate usernames and passwords against data stored in SQL Server. In the Button1_Click event, a connection is made to SQL Server. (For security reasons, you should store your connection string in the web.config file.) Two parameters are passed in — the inputs from TextBox1 and TextBox2 .Ifa result is returned, the RedirectFromLoginPage() method is invoked. Using the Login Control with Forms Authentication You have seen how to use ASP.NET forms authentication with standard ASP.NET server controls, such as simple TextBox and Button controls. You can also use the ASP.NET server controls — such as the Login server control — with your custom-developed forms-authentication framework instead of using other controls. This really shows the power of ASP.NET — you can combine so many pieces to construct the solution you want. Listing 21-10 shows a modified Login.aspx page using the new Login server control. Listing 21-10: Using the Login server control on the Login.aspx page VB < %@ Page Language="VB" % > < script runat="server" > Protected Sub Login1_Authenticate(ByVal sender As Object, _ ByVal e As System.Web.UI.WebControls.AuthenticateEventArgs) If (Login1.UserName = "BillEvjen" And Login1.Password = "Bubbles") Then FormsAuthentication.RedirectFromLoginPage(Login1.UserName, _ Login1.RememberMeSet) Else Response.Write("Invalid credentials") End If End Sub < /script > < html xmlns="http://www.w3.org/1999/xhtml" > < head runat="server" > < title > Login Page < /title > < /head > < body > < form id="form1" runat="server" > < div > < asp:Login ID="Login1" runat="server" OnAuthenticate="Login1_Authenticate" > < /asp:Login > < /div > < /form > < /body > < /html > C# < %@ Page Language="C#" % > 1014 Evjen c21.tex V2 - 01/28/2008 3:15pm Page 1015 Chapter 21: Security < script runat="server" > protected void Login1_Authenticate(object sender, AuthenticateEventArgs e) { if (Login1.UserName == "BillEvjen" && Login1.Password == "Bubbles") { FormsAuthentication.RedirectFromLoginPage(Login1.UserName, Login1.RememberMeSet); } else { Response.Write("Invalid credentials"); } } < /script > Because no Button server control is on the page, you use the Login control’s OnAuthenticate attribute to point to the authentication server-side event — Login1_Authenticate . The event takes care of the authorization lookup (although the values are hardcoded in this example). The username text box of the Login control can be accessed via the Login1.UserName declaration, and the password can be accessed using Login1.Password .The Login1.RememberMeSet property is used to specify whether to persist the authentication cookie for the user so that he is remembered on his next visit. This example is a bit simpler than creating your own login form using TextBox and Button controls. You can give the Login control a predefined look-and-feel that is provided for you. You can also get at the subcontrol properties of the Login control a bit more easily. In the end, it really is up to you as to what methods you employ in your ASP.NET applications. Looking Closely at the FormsAuthentication Class As you can tell from the various examples in the forms authentication part of this chapter, a lot of what goes on depends on the FormsAuthentication class itself. For this reason, you should learn what that class is all about. FormsAuthentication provides a number of methods and properties that enable you to read and con- trol the authentication cookie as well as other information (such as the return URL of the request). The following table details some of the methods and properties available in the FormsAuthentictation class. Method/Property Description Authenticate This method is used to authenticate credentials that are stored in a configuration file (such as the web.config file). Decrypt Returns an instance of a valid, encrypted authentication ticket retrieved from an HTTP cookie as an instance of a FormsAuthenticationTicket class. Encrypt Creates a string which contains a valid encrypted authentication ticket that can be used in an HTTP cookie. FormsCookieName Returns the name of the cookie for the current application. FormsCookiePath Returns the cookie path (the location of the cookie) for the current application. GetAuthCookie Provides an authentication cookie for a specified user. 1015 Evjen c21.tex V2 - 01/28/2008 3:15pm Page 1016 Chapter 21: Security Method/Property Description GetRedirectUrl Returns the URL t o which the user is redirected after being authorized by the login page. HashPasswordFor Storing InConfigFile Creates a hash of a provided string password. This method takes two parameters — o ne is the password and the other is the type of hash to perform on the string. Possible hash values include SHA1 and MD5 . Initialize Performs an initialization of the FormsAuthentication class by reading the configuration settings in the web.config file, as well as getting the cookies and encryption keys used in the given instance of the a pplication. RedirectFromLogin Page Performs a redirection of the HTTP request back to the original requested page. This should be performed only after the user has been authorized to proceed. RenewTicketIfOld Conditionally updates the sliding expiration on a FormsAuthenticationTicket instance. RequireSSL Specifies whether the cookie should be transported via SSL only (HTTPS). SetAuthCookie Creates an authentication ticket and attaches it to a cookie that is contained in the outgoing response. SignOut Removes the authentication ticket. SlidingExpiration Provides a Boolean value indicating whether sliding expiration is enabled. Passport Authentication Another method for the authentication of your end users is using Microsoft’s Passport identity system. Users with a passport account can have a single sign-on solution, meaning that he needs only those credentials to log in to your site and into other Passport-enabled sites and applications on the Internet. When your application is enabled for Passport authentication, the request is actually redirected to the Microsoft Passport site where the user can enter his credentials. If the authentication is successful, the user is then authorized to proceed, and the request is redirected back to your application. Very few Internet sites and applications use Microsoft’s Passport technologies. In fact, Microsoft has completely de-emphasized Passport in 2005, and most companies interested in global authentication/ authorization standards are turning toward the Project Liberty endeavors for a solution ( www.projectliberty.org ). Authenticating Specific Files and Folders You may not want to require credentials for each and e very page or resource in your application. For instance, you might have a public Internet site with pages anyone can access without credentials, although you might have an administration section as part of your application that may require authen- tication/authorization measures. 1016 Evjen c21.tex V2 - 01/28/2008 3:15pm Page 1017 Chapter 21: Security URL authorization enables you to use the web.config file to apply the settings you need. Using URL authorization, you can apply any of the authentication measures to only specific files or folders. Listing 21-11 shows an example of locking down a single file. Listing 21-11: Applying authorization requirements to a single file < configuration > < system.web > < authentication mode="None" / > < ! The rest of your web.config file settings go here > < /system.web > < location path="AdminPage.aspx" > < system.web > < authentication mode="Windows" / > < authorization > < allow users="ReutersServer \ EvjenB" / > < deny users="*" / > < /authorization > < /system.web > < /location > < /configuration > This web.config construction keeps the Web application open to the general public while, at the same time, it locks down a single file contained within the application — the AdminPage.aspx page. This is accomplished through the < location > element. < location > takes a single attribute ( path )tospecify the resource defined within the < system.web > section of the web.config file. In the example, the < authentication > and < authorization > elements are used to provide the authen- tication and authorization details for the AdminPage.aspx page. For this page, Windows authentication is applied, and the only user allowed access is EvjenB in the ReutersServer domain. You can have as many < location > sections in your web.config file as you want. Programmatic Authorization So far, you have seen a lot of authentication examples that simply provide a general authorization to a specific page or folder within the application. Yet, you may want to provide more granular authorization measures for certain items on a page. For instance, you might provide a link to a specific document only for users who have an explicit Windows role. Other users may see something else. You also might want additional commentary or information for specified users, while other users see a condensed version of the information. Whatever your reason, this role-based authorization practice is possible in ASP.NET by working with certain objects. You can use the Page object’s User property, which provides an instance of the IPrincipal object. The User property provides a single method and a single property: ❑ Identity : This property provides an instance of the System.Security.Principal.IIdentity object for you to get at specific properties of the authenticated user. 1017 . browser. The real power of forms authentica- tion is shown in the Login.aspx page presented in Listing 21 -5. Listing 21 -5: The Login.aspx page VB < %@ Page Language="VB" % > < script. authenticationtokenisinplace.Ifthepropertokenisnotfound, the request is directed to the specified login page (in this example, Login.aspx ). Looking at the URL in the browser, you can see that ASP. NET is using. credentials input by a user against values stored in Microsoft’s SQL Server. The code for this is presented in Listing 21-9. Listing 21-9: Checking credentials in SQL Server (Login.aspx) VB < %@