<%@ WebService Language="C#" Class="SecureSample" %>

using System.Web.Services;
using System.Web.Security;

public class SecureSample : WebService
{
  [WebMethod]
  public string WhoAreYou()
  {
    return User.Identity.Name;
  }

  [WebMethod]
  public bool Authenticate(string username, string password)
  {
    if ((username == "John") && (password == "password"))
    {
      FormsAuthentication.SetAuthCookie(username, true);
      
      return true;
    }

    return false;
  }
}