Assuming you have followed the previous post and now have a Silverlight client that can authenticate users via the membership providers then the next step is to write your web services.
1. Create Service
Although you can as a web service to the current ASP.NET site it’s probably more likely that you’ll want a separate web service project so Add->New Project->Web Service. If you’re using the default templates then you should see a HelloWorld web method created for you.
[WebMethod]
public string HelloWorld()
{
return "Hello World";
}
2. Connect the Service to the same Membership database
As I mentioned in my previous post, you’re better off providing your own connection string for the membership store, so now you’ve created a new site you have to add the same connection string to the web service, something like;
<connectionStrings>
<remove name="LocalSqlServer"/>
<add name="LocalSqlServer" connectionString="Data Source=.\MySQLServer;Initial Catalog=aspnetdb;Integrated Security=True" providerName="System.Data.SqlClient"/>
</connectionStrings>
3. Add a reference from your Silverlight client to the service
In the Silverlight project Add Service Reference and press discover. If your service doesn’t show make sure you’ve built the project, VS sometimes won’t spot the new project until it has been built.
4. Add the code to call your service
Nothing special here except you may want to catch exceptions because the user isn’t authenticated (forgive the rubbish use of Execption here);
private void TestService_Click(object sender, RoutedEventArgs e)
{
ServiceReference1.Service1SoapClient testService = new ApplicationServicesDemo.ServiceReference1.Service1SoapClient();
testService.HelloWorldCompleted += new EventHandler<ApplicationServicesDemo.ServiceReference1.HelloWorldCompletedEventArgs>(testService_HelloWorldCompleted);
testService.HelloWorldAsync();
}
void testService_HelloWorldCompleted(object sender, ApplicationServicesDemo.ServiceReference1.HelloWorldCompletedEventArgs e)
{
try
{
TestService.Content = "Test -" + e.Result;
}
catch (Exception)
{
TestService.Content = "Please sign in";
}
}
To handle the exception correctly you need to delve into the inner exception but hopefully you get the idea.
5. Secure the web method
The easiest way to secure the method is to add a System.Security.Permissions attribute to the method;
[WebMethod]
[PrincipalPermission(SecurityAction.Demand, Authenticated = true)]
public string HelloWorld()
{
return "Hello World";
}
There you have it. One "secure" web service. If your user is authenticated via membership then they’ll have access, if they don’t then the service will tell a white lie and say the service doesn’t exist.
IT Bytes 
hi Pauliom, i wanna know which was your previous post about integrating Asp.Net Membership on Silverlight app …it would be helpfull thx
This is the link you’re looking for (sounds a bit like Star Wars);
https://pauliom.wordpress.com/2009/01/18/integrating-silverlight-with-asp-net-authentication/
yes, sounds epical! …i’ve been gathering info about asp.net auth so thanks for the link.