Authentication on Arduino Ethernet

hi eveyone, Excuse my English but I’m Italian, so speak simple please.
I have a problem with Arduino uno and Ethernet shield:
I made a web service HTTP based that allows me to turn on and off two led by the browser.

#include <SPI.h>
#include <Client.h>
#include <Ethernet.h>
#include <Server.h>

//DETERMINA IL MAC E L'IP DELLA PAGINA WEB
byte mac[] = { 0xDE, 0xAD, 0xBE, 0xEF, 0xFE, 0xEA };   
byte ip[] = { 192, 168, 0, 133 }; // indirizzo IP della shield  
byte gateway[] = { 192, 168, 0, 1 }; // indirizzo ip del router  
byte subnet[] = { 255, 255, 255, 0 }; //subnet mask  
EthernetServer server(80);  

//PORTA DI COMUNICAZIONE			


//SCRIVE IL NUMERO DI PIN CORRISPONDENTE AI LED
int ledPin1 = 9; 
int ledPin2 = 8;

//LUNGHEZZA DELLA STRINGA INVIATA
String readString = String(30);

//IMPOSTA ALL'AVVIO I LED SPENTI
boolean LEDON1 = false; 
boolean LEDON2 = false; 

void setup(){
  Ethernet.begin(mac, ip, gateway, subnet);  
  pinMode(ledPin1, OUTPUT);  
  pinMode(ledPin2, OUTPUT); 
  Serial.begin(9600);
}

void loop(){
  EthernetClient client = server.available();
  if (client) //SE ESISTE UN CLIENTE
  {
    while (client.connected()) // SE IL CLIENTE E' CONNESSO
    {
      if (client.available()) //SE E' TUTTO OK PER INIZIARE
      {
        char c = client.read(); //LEGGI I SINGOLI CARATTERI INVIATI
        if (readString.length() < 100) 
        {
          readString += c; //CONCATENA I CARATTERI
        }  
        if (c == '\n') //VEDE SE C'E' IL CARATTERE DI FINE STRINGA, PER INDIVIDUARE CHE E' FINITA
        {
          if(readString.indexOf("L1=1") > 0) //IMPOSTA UNA VARIABILE DI TIPO BOLEANA (VERO-FALSO) PER GLI STATI DEL LED
          {
            LEDON1 = true;
          } 
          else if (readString.indexOf("L2=1") > 0) 
          {
            LEDON2 = true;             
          }
          else if(readString.indexOf("L1=0") > 0)
          {
            LEDON1 = false;
          } 
          else if (readString.indexOf("L2=0") > 0) 
          {
            LEDON2 = false;             
          }

          //CREA LA PAGINA HTML (VERRA' AGGIORNATA AD OGNI ISTRUZIONE NUOVA)
          client.println("HTTP/1.1 200 OK");
          client.println("Content-Type: text/html");
          client.println();
          client.println("<html><head></head><body>");

          //TITOLO LED 1
          client.println("<h1>Led 1</h1>");

          //OPERAZIONI DA FARE QUANDO SI CLICCA PER ATTIVARE LEDON1:  
          if (LEDON1) { 
            digitalWrite(ledPin1, HIGH);   
            client.println("Stato: ON
");
          } 
          else {

            //OPERAZIONI DA FARE QUANDO SI CLICCA PER SPEGNERE LEDON1:  
            digitalWrite(ledPin1, LOW ); 
            client.println("Stato: OFF
"); 
          }

          //CREA I PULSANTI RELATIVI A LED1    
          client.println("<a href='?L1=0'>OFF</a>");
          client.println("<a href='?L1=1'>ON</a>");

          //INSERISCE IL DIVISORE
          client.println("
______________________________
");

          //TTOLO LED2
          client.println("<h1>Led 2</h1>");

          //OPERAZIONI DA FARE QUANDO SI CLICCA PER ATTIVARE LEDON2:  
          if (LEDON2) { 
            digitalWrite(ledPin2, HIGH);  
            client.println("Stato: ON
"); 
          } 
          else { 

            //OPERAZIONI DA FARE QUANDO SI CLICCA PER SPEGNERE LEDON2:    
            digitalWrite(ledPin2, LOW); 
            client.println("Stato: OFF
"); 
          } 

          //CREA I PULSANTI RELATIVI A LED2
          client.println("<a href='?L2=0'>OFF</a>");
          client.println("<a href='?L2=1'>ON</a>");

          //CHIUDE I TAG HTML PER LA PAGINA
          client.println("</body></html>");

          //SI PREPARA PER UNA NUOVA ISTRUZIONE
          readString="";

          //TERMINA LE OPERAZIONI CLIENTE
          client.stop();
        }
      }
    }
  }
}

the problem is that i want an authentication on the page, because I do not want anyone can turn on the lights.
thanks to all,
Simone

the problem is that i want an authentication on the page

What really is the problem?

The client makes a request. Regardless of the request, you respond exactly the same way.

What you need to do is exactly what a real server does. If the request does not contain a token that the server issued, it returns a login page, instead. When the user supplies known information, that the server validates, the server responds with a token that the client is supposed to remember and supply in future requests, until the token expires.

Typically, the client stores the token in a cookie, valid for some period of time.

You should NOT be expecting to be able to do this without understanding the process for clients and servers on larger computers. Or, being able to search for any of the hundreds of requests for how to do this, with solutions.