Beginning Web Development, Silverlight, and ASP.NET AJAX

CHAPTER 10 ■ .NET 3.0: PROGRAMMING WITH CARDSPACE 247
The Use Card! button is defined with this markup:
Use Card!
Upon clicking the button, the JavaScript function GoGetIt is invoked. Here’s the
function:
function GoGetIt()
{
var xmltkn=document.getElementById("_xmltoken");
var thetextarea = document.getElementById("xmltoken");
thetextarea.value = xmltkn.value ;
}
This script uses the element _xmltoken to get its value and load that into a var that will
fill a text box on the page. The _xmltoken field is a CardSpace object, whose definition looks
like this:
This is how you use CardSpace on a page—by declaring an object of type
application/x-informationcard and naming it. There are a number of properties supported
by this object, including the facility to specify the data that’s required by the site.
Remember the earlier example in which the last name, first name, and so on were
required data from the site—it is the requiredClaims property that dictates this. As you
can see, it contains a list of the schemas of the required values.
When you query its value property, the object invokes the CardSpace client and
allows you to specify a card. Should you specify and send a card, the value will become
the token associated with that card; otherwise it will be null. The JavaScript code then
loads the value of the token into the hidden text field xmltoken.
Next, when the user clicks “Sign in now!” they are in fact invoking a standard HTML
form whose action is the SignedIn.aspx page, and one of whose elements is the hidden
text field. This causes the token to be submitted to SignedIn.aspx from where it can be
parsed.