public void LogOn(UserModel user)
 {
     if (!this.users.Contains(user))
     {
         throw new SecurityException();
     }
 }
        public void LogOn(UserModel user)
        {
            Thread.Sleep(TimeSpan.FromSeconds(1));

            if (!this.users.Contains(user))
            {
                throw new SecurityException();
            }
        }
 public void LogOff(UserModel user)
 {
     Thread.Sleep(TimeSpan.FromSeconds(1));
 }
 public void LogOff(UserModel user)
 {
 }