C# Program to Illustrate User Authentication

// C# implementation of User Authentication
// Include namespace system
using System;
using System.Text.RegularExpressions;
public class GFG
{
    public const String NAME = "GEEKSFORGEEKS";
    public const String USERNAME = "GEEKS";
    public const String PASSWORD = "Geeks@123";
    public static bool SignUp(String name, String userName, String password)
    {
        // Verify password length
        if (password.Length < 8 || password.Length > 16)
        {
            Console.WriteLine("Password must be in range of 8-16 characters.");
            return false;
        }
          Regex regex = new Regex("^(?=.*[a-z])(?=.*[A-Z])(?=.*\\d)(?=.*[@$!%*?&])[A-Za-z\\d@$!%*?&]+");

      if (regex.Match(password).Value=="")
        {
            Console.WriteLine("Password must contains alphanumeric characters and atleast 1 special symbol.");
            return false;
        }
        
        return true;
    }
    public static bool Login(String userName, String password)
    {
        if (userName == USERNAME && password == PASSWORD)
        {
            return true;
        }
        Console.WriteLine("Enter Valid Username Or Password!");
        return false;
    }
    public static void Main(String[] args)
    {
        // Try SignUp With Invalid Password    (Length < 8)
        Console.WriteLine("User 1 : ");
        if (GFG.SignUp(NAME, USERNAME, "Geeks12"))
        {
            Console.WriteLine("Account Created Successfully.");
        }
        // Try SignUp With Invalid Password    (Excluding Special Symbol)
        Console.WriteLine("User 2 : ");
        if (GFG.SignUp(NAME, USERNAME, "Geeks123"))
        {
            Console.WriteLine("Account Created Successfully.");
        }
        // With Valid Password
        Console.WriteLine("User 3 : ");
        if (GFG.SignUp(NAME, USERNAME, PASSWORD))
        {
            Console.WriteLine("Account Created Successfully.");
        }
        // With Wrong Username Or Password
        Console.WriteLine("User 2 : ");
        if (GFG.Login(USERNAME, "Geeks123"))
        {
            Console.WriteLine("Log In Successful.");
        }
        // With Valid Username And Password
        Console.WriteLine("User 3 : ");
        if (GFG.Login(USERNAME, PASSWORD))
        {
            Console.WriteLine("Log In Successful.");
        }
    }
}