public abstract class CustomAuthenticator

// Custom autenticator class. 
// Note: For brevity, some details are intentionally omitted. 

public class TestAuthenticator : CustomAuthenticator
{
   // Empty constructor required
   public TestAuthenticator() : base()
   {
   }

   protected override IIdentity AuthenticateTokenCore(AuthenticationContext context)
   {
       string userName = String.Empty;
       string portalConnectionInfo = null;
       // Assuming the token is contained in the request header
       string token = context.Context.Request.Headers["token"];

       System.Configuration.Configuration webConfig =
           System.Web.Configuration.WebConfigurationManager.OpenWebConfiguration(null);

       // This exampel relies on custom settings.
       if (0 < webConfig.AppSettings.Settings.Count)
       {
           System.Configuration.KeyValueConfigurationElement customSetting =
               webConfig.AppSettings.Settings["PortalConnectionInfo"];

           // Required setting throw exception if it doesn't exist.
           if (null != customSetting)
           {
               portalConnectionInfo = customSetting.Value;
           }
           else
           {
               // Error, throw exception
           }
       }
       else
       {
           // Error, throw exception
       }

       // 
       // Authenticate against the Portal server using
       // portalConnectionInfo, assign the user name
       // corresponding to the <c>token</c> to the 
       // <c>userName</c> parameter. 
       // 

       // Use the CreateIdentity helper method to create an
       // IIdentity object of correct type. 
       return CreateIdentity(userName);
   }
}