You create a Microsoft ASP.NET application by using the Microsoft .NET Framework
version 3.5.

You create a login Web form by using the following code fragment.

<asp:ScriptManager ID=”ScriptManager1″ runat=”server” />
<asp:TextBox runat=”server” ID=”txtUser” Width=”200px” />
<asp:TextBox runat=”server” ID=”txtPassword” Width=”200px” />
<asp:Button runat=”server” ID=”btnLogin” Text=”Login” OnClientClick=”login(); return false;” />

When a user clicks the btnLogin Button control, the login() client-side script is called
to authenticate the user. The credentials provided in the TextBox controls are used to
call the client-side script.

You also add the following client-script code fragment in the Web form. (Line numbers
are included for reference only.)

01 <script type=”text/javascript”>
02 function login() {
03 var username = $get(‘txtUser’).value;
04 var password = $get(‘txtPassword’).value;
05
06 // authentication logic.
07 }
08 function onLoginCompleted(validCredentials, userContext,
09 methodName)
10 {
11 // notify user on authentication result.
12 }
13
14 function onLoginFailed(error, userContext, methodName)
15 {
16 // notify user on authentication exception.
17 }
18 </script>

The ASP.NET application is configured to use Forms Authentication. The ASP.NET AJAX authentication service is activated in the Web.config file.

You need to ensure that the following workflow is maintained:

– On successful authentication, the onLoginCompleted client-script function is called to notify the user.
– On failure of authentication, the onLoginFailed client-script function is called to display an error message.

Which code segment should you insert at line 06?

A.
var auth = Sys.Services.AuthenticationService;
auth.login(username, password, false, null, null,onLoginCompleted, onLoginFailed, null);

B.
var auth = Sys.Services.AuthenticationService;
auth.set_defaultFailedCallback(onLoginFailed);var validCredentials = auth.login(username, password, false, null, null, null, null, null);
if (validCredentials)onLoginCompleted(true, null, null);
elseonLoginCompleted(false, null, null);

C.
var auth = Sys.Services.AuthenticationService;auth.set_defaultLoginCompletedCallback(onLoginCompleted);
try { auth.login(username, password, false, null, null, null, null, null);
}catch (err) { onLoginFailed(err, null, null);}

D.
var auth = Sys.Services.AuthenticationService;
try { var validCredentials = auth.login(username, password, false, null, null, null, null, null);
if (validCredentials) onLoginCompleted(true, null, null);
else onLoginCompleted(false, null, null);
}
catch (err) { onLoginFailed(err, null, null);}