Make username work on WebGL

hi, i got a project that requires a game , made by WebGL , with username and password but work offline. so i following up some tutorials that can make username and password work offline. but i got some problem that didnt work on WebGL. only work with exe. here's my code.

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 using UnityEngine.UI;
 using System;
 using System.Text.RegularExpressions;
 using UnityEngine.SceneManagement;
 
 public class Register : MonoBehaviour {
 
     public GameObject username;
     public GameObject kantorWilayah;
     public GameObject statusCabang;
     public GameObject cabangKoord;
     public GameObject kodeCabang;
     public GameObject inisialCabang;
     public GameObject alamat;
     public GameObject password;
     public GameObject confirmPassword;
     private string Username;
     private string KantorWilayah;
     private string StatusCabang;
     private string CabangKoord;
     private string KodeCabang;
     private string InisialCabang;
     private string Alamat;
     private string Password;
     private string ConfirmPassword;
     private string form;
 
     public void Back()
     {
         SceneManager.LoadScene ("AdminPanel");
     }
 
     public void EditID()
     {
         SceneManager.LoadScene ("EditID");
     }
 
     public void RegisterButton()
     {
         bool UN = false;
         bool KW = false;
         bool SC = false;
         bool CK = false;
         bool KC = false;
         bool IC = false;
         bool ALM = false;
         bool PW = false;
         bool CPW = false;
         //jika terisi username
         if (Username != "") {
             if (!System.IO.File.Exists (@"D:/UnityAdministrationFolder/" + Username + ".txt")) {
                 UN = true;
             } else {
                 print ("Kepake");
             }
         } else {
             print ("Kosong");
         }
         //password
         if(Password != "")
         {
             if(Password.Length > 5)
             {
                 PW = true;
             }
             else{
                 Debug.LogWarning("Password kudu lebih dr 6 karakter");
             }
         }
         else{
             Debug.LogWarning("Password kosong");
         }
         if(ConfirmPassword != "")
         {
             if(ConfirmPassword == Password)
             {
                 CPW = true;
             }else{
                 Debug.LogWarning("Konfirmasi Password ga sama");
             }
         }else{
             Debug.LogWarning("Konfirmasi Password kosong");
         }
         //KantorWilayah
         if (KantorWilayah != "") {
             KW = true;
         }
         if (StatusCabang != "") {
             SC = true;
         }
         if (CabangKoord != "") {
             CK = true;
         }
         if (KodeCabang != "") {
             KC = true;
         }
         if (InisialCabang != "") {
             IC = true;
         }
         if (Alamat != "") {
             ALM = true;
         }
 
         if(UN == true&&PW == true&&CPW == true&&KW == true&&SC == true&&CK == true&&KC == true&&IC == true&&ALM == true)
         {
             bool Clear = true;
             int i = 1;
             foreach(char c in Password)
             {
                 if(Clear)
                 {
                     Password = "";
                     Clear = false;
                 }
                 i++;
                 char Encrypted = (char)(c * i);
                 Password += Encrypted.ToString();
             }
 
             form = (Username + Environment.NewLine + KantorWilayah + Environment.NewLine + StatusCabang + Environment.NewLine + KodeCabang + Environment.NewLine + InisialCabang + Environment.NewLine + Alamat + Environment.NewLine + Environment.NewLine + Password);
             System.IO.File.WriteAllText(@"D:/UnityAdministrationFolder/" + Username + ".txt", form);
             username.GetComponent<InputField> ().text = "";
             kantorWilayah.GetComponent<InputField> ().text = "";
             statusCabang.GetComponent<InputField> ().text = "";
             cabangKoord.GetComponent<InputField> ().text = "";
             kodeCabang.GetComponent<InputField> ().text = "";
             inisialCabang.GetComponent<InputField> ().text = "";
             alamat.GetComponent<InputField> ().text = "";
             password.GetComponent<InputField> ().text = "";
             confirmPassword.GetComponent<InputField> ().text = "";
             SceneManager.LoadScene ("Title");
         }
     }
     
     // Update is called once per frame
     void Update () {
         if (Input.GetKeyDown (KeyCode.Tab)) {
             if (kantorWilayah.GetComponent<InputField> ().isFocused) {
                 statusCabang.GetComponent<InputField> ().Select ();
             }
             if (statusCabang.GetComponent<InputField> ().isFocused) {
                 cabangKoord.GetComponent<InputField> ().Select ();
             }
             if (cabangKoord.GetComponent<InputField> ().isFocused) {
                 kodeCabang.GetComponent<InputField> ().Select ();
             }
             if (kodeCabang.GetComponent<InputField> ().isFocused) {
                 inisialCabang.GetComponent<InputField> ().Select ();
             }
             if (inisialCabang.GetComponent<InputField> ().isFocused) {
                 alamat.GetComponent<InputField> ().Select ();
             }
             if (alamat.GetComponent<InputField> ().isFocused) {
                 username.GetComponent<InputField> ().Select ();
             }
             if (username.GetComponent<InputField> ().isFocused) {
                 password.GetComponent<InputField> ().Select ();
             }
             if (password.GetComponent<InputField> ().isFocused) {
                 confirmPassword.GetComponent<InputField> ().Select ();
             }
         }
 
         if (Input.GetKeyDown (KeyCode.Return)) {
             if (Username != ""&&StatusCabang != ""&&Password != ""&&ConfirmPassword != ""&&KantorWilayah != ""&&CabangKoord != ""&&KodeCabang != ""&&InisialCabang != ""&&Alamat != "") {
                 RegisterButton ();
             }
         }
         Username = username.GetComponent<InputField> ().text;
         Password = password.GetComponent<InputField> ().text;
         ConfirmPassword = confirmPassword.GetComponent<InputField> ().text;
         KantorWilayah = kantorWilayah.GetComponent<InputField> ().text;
         StatusCabang = statusCabang.GetComponent<InputField> ().text;
         CabangKoord = cabangKoord.GetComponent<InputField> ().text;
         KodeCabang = kodeCabang.GetComponent<InputField> ().text;
         InisialCabang = inisialCabang.GetComponent<InputField> ().text;
         Alamat = alamat.GetComponent<InputField> ().text;
     }
 }
 

hope someone can help. i looking for a solution out there , but i didnt understand how to use ExternalCall or ExternalEval. someone can help me? thanks for any help