How to Provide security After LogOut

See more:

WCF

LINQ

.NET4

Silverlight4

I developed a Silverlight application that contains Login.xaml and UserDetails.xaml.

Now I created a WCF service for doing a login check like this:

//service for Login
       [OperationContract]
       public ClsFirstGuardion Login(string UserName, string Password)
       {ClsFirstGuardion list = new ClsFirstGuardion();
           DBDataContext db = new DBDataContext();
           var v = from i in db.fg0au000s
                   where i.Username == UserName && i.Password == Password
                   select new { i.Username };
           foreach (var i in v)
           {       if (i == null)
               {
                   list.PMessage = "invalid";
               }
               else if (i != null)
               {
                   list.PMessage = i.Username;
               }
           }
           return list;
       }

And in Login.xaml.cs, I called an event handler like this:

ServiceReference1.WcfServiceClient client = new ServiceReference1.WcfServiceClient("CustomBinding_WcfService", servAddr);
                 client.LoginCompleted += new EventHandler<LoginCompletedEventArgs>(client_LoginCompleted);
                 client.LoginAsync(textBox1.Text, passwordBox1.Password); 

void client_LoginCompleted(object sender, LoginCompletedEventArgs e)
         {
             ClsFirstGuardion cs = e.Result;
             if (cs.PMessage == null)
             {
                 txtbloxLoginMessage.Text = "The UserName or Password you Entered is InCorrect";
             }
             else
             { string StudentId = cs.PMessage;
                  this.NavigationService.Navigate(new Uri(String.Format("UserDetails.Xaml?id=", StudentId), UriKind.Relative));
             }
         }

Now I access the query string value In UserDetails.xaml page and I displayed that name.

Now my requirement is how to provide a logout functionality from this page?
I should not access this page(UserDetails.Xaml) after clicking logout.
In the logout event I wrote code to just navigate to Login.xaml page.

My problem is when I am clicking the browser's back button after clicking the logout button.
As it is then displaying UserDetails.xaml page. I need a solution for this requirement.

Can anyone please give me a procedure for my requirement?

Thanks,
Vijay