public static void saveUser(string username, string password) {
     User entity = new User();
     var user = entity.AddLike<IUser>();        
     user.username = username;
     user.password = password;
     MongoDBController.Usuarios.Save(user);
 }
 public static void saveUser(User user)
 {
     var obj = user.AddLike<IUser>();
     MongoDBController.Empresas.Save(obj);
 }