input: Write a python function to simulate a login system with token and password authentication.
  assert login_system("user1", password="password123") == "Login successful"
  assert login_system("user1", token="valid_token_123") == "Login successful"
  assert login_system("user1", password="wrong_password") == "Password login failed, unknown user or wrong password!"
  assert login_system("user1", token="invalid_token") == "Token login failed, unknown user or wrong password!"
output: def login_system(username, password=None, token=None):
      users = {
          "user1": {"password": "password123", "token": "valid_token_123"}
      }
      
      if username in users:
          if password and users[username]["password"] == password:
              return "Login successful"
          elif token and users[username]["token"] == token:
              return "Login successful"
      
      if password:
          return "Password login failed, unknown user or wrong password!"
      elif token:
          return "Token login failed, unknown user or wrong password!"