Codice PHP:
/*INDEX.PHP*/
<!DOCTYPE html>
<
html>
    <
head>
        <
title>index.php</title>
        <
meta name="viewport" content="width=device-width, initial-scale=1.0">
        <
meta charset="utf-8">
         <
script src="https://ajax.googleapis.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
        <script src="https://cdnjs.cloudflare.com/ajax/libs/mathjs/3.14.1/math.min.js"></script>
        <link href="config.css" type="text/css" rel="stylesheet">
    </head>

    <body>

        <div id="form-riconoscimento">
            <h4>modulo di riconoscimento</h4>
            <button onclick="generaUsername()">genera username</button>
                <table>
                    <form method="post" action="server.php">

                        <tr>
                            <td><input type="text" name="username" id="username" required></td>
                        </tr>    
                        <tr>    
                            <td><input type="password" name="password" placeholder="password"></td>
                        </tr>
                        <tr>
                            <td><input type="radio" name="opzioneUtente" value="registrareUtente">registrasi</td></tr>
                        <tr>
                            <td><input type="radio" name="opzioneUtente" value="loggareUtente" checked>accedere</td>
                        </tr>
                        <tr>
                            <td><input type="submit" value="invio"></td></tr>
                    </form>
                </table>
        </div>
        <script type="text/javascript">

            function generaUsername(){
                        codiceAlfa = "HAvc13nmsdw";
            caratteri = codiceAlfa.split(""); //return array
            codici = [];
                  for(i=0; i<=caratteri.length; i++){
                      codici.push(caratteri[math.randomInt(caratteri.length)]) ;
                  }
                codice = codici.join(""); //return string
                document.getElementById("username").value=codice;
            }
            
           
                username = document.getElementById("username");
            
                if(navigator.userAgent == "Mozilla/5.0 (Windows NT 6.1; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/69.0.3497.100 Safari/537.36")
                {username.setAttribute("value", "crom");
                }
                else if(navigator.userAgent == "Mozilla/5.0 (Windows NT 6.1; Win64; x64; rv:62.0) Gecko/20100101 Firefox/62.0")
                {username.setAttribute("value", "firefox");  }    
             
  
        </script> 

</body>
</html> 
Codice PHP:
<?php
/*SERVER.PHP*/
session_start();
$conex mysql_connect('localhost''root');
mysql_select_db("my_laboraccio"$conex);

/*variabili di index.php*/
$uname $_POST['username'];
$pw =  $_POST['password'];
$opzioneUtente $_POST['opzioneUtente'];

/*variabili di profilo.php */
echo $_GET['sms'];




if(
$_POST['sessione'] == "logout") {
    
session_unset();
    
session_destroy();
    
header("Refresh:10; url=http://www.laboraccio.altervista.org/");
    echo 
"sessione scaduta";
}
    function 
registraUtente(){
        global 
$uname;
        echo 
$uname;
        global 
$pw;
        
$sql "SELECT * FROM utenti WHERE username='$uname'";
        
$resource mysql_query($sql) or die (mysql_error());
        
$result mysql_num_rows($resource);
        echo 
$result;
        if(
$result == 0) {
            
$sql "INSERT INTO utenti (id, username, password) VALUES (NULL, '$uname', '$pw')";
            
mysql_query($sql);
            
header("Refresh:10; url=http://www.laboraccio.altervista.org/");
              echo 
"nuovo utente creato";
 
            echo 
"registrazione completata";
        }
        elseif(
$result == 1){
            echo 
"username gia in uso, riprova con un altro";
              
header("Refresh:10; url=http://www.laboraccio.altervista.org/");
           }
    }
    
        function 
loggareUtente(){
        global 
$uname;
        global 
$pw;
        
$sql "SELECT * FROM utenti WHERE username='$uname' AND password='$pw'";
        
$resource mysql_query($sql) or die (mysql_error());
        
$result mysql_num_rows($resource);
        if(
$result == 1) {
            
$_SESSION['username'] = $uname;
            
$_SESSION['password'] = $pw;
            echo 
"benvenuto alla tua area personale".$uname;
            
header("location:http://www.laboraccio.altervista.org/profilo.php");

        
        }
        elseif(
$result == 0) {print "utente non valido";  
        
header("Refresh:10; url=http://www.laboraccio.altervista.org/");
        }

    
    }


if(
$opzioneUtente == 'registrareUtente'){
    
registraUtente();
}
elseif(
$opzioneUtente == "loggareUtente") {
    
loggareUtente();
}

?>
Codice PHP:
<?php

/*PROFILO.PHP*/
session_start();

if(!isset(
$_SESSION['username'])) {
    
header("location: http://laboraccio.altervista.org/");
}

if(isset(
$_SESSION['username'])){
echo 
$_SESSION['username'];
}
?>
Ogni volta che faccio login mi rimanda sempre al index