LoginModule.cs

using System;
using UnityEngine;

[DefaultExecutionOrder(ExecuteOrder.LOGIN_INIT)]
public class LoginModule : MonoBehaviour
{
    void Awake()
    {
        byte[] bytes = new byte[0];
        
        ILoginModule loginModule = new LocalLoginModule();
        loginModule.Login(bytes, result =>
        {
            switch ((ELoginError)result) {
                case ELoginError.Undefined:
                    Debug.Log("Undefined");
                    break;
                case ELoginError.PortClosed:
                    Debug.Log("Login Failed");
                    break;
                case ELoginError.Success:
                    Debug.Log("Login success");
                    break;
                default:
                    throw new ArgumentOutOfRangeException(nameof(result), result, null);
            }
        });
    }
}

public class LocalLoginModule : ILoginModule {
    
    public void Login(byte[] bytes, Action<int> loginResult)
    {
        Debug.Log("Try Log in...");
        
        if (UnityEngine.Random.Range(0, 10) % 9 == 0) {
            loginResult.Invoke((int) ELoginError.PortClosed);
        }
        else {
            loginResult.Invoke((int) ELoginError.Success);
        }
    }
}

public interface ILoginModule {
    void Login(byte[] bytes, Action<int> loginResult);
}

public enum ELoginError {
    Undefined = -1,
    Success = 0,
    PortClosed = 100,
}