AJAX Chat Register Code

<!DOCTYPE html>
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<html>
    <head>
        <meta charset="UTF-8">
        <title>Register to chat</title>
        <link type="text/css" rel="stylesheet" href="css/MyBB.css">
    </head>
    <body>
        <form method="post" onclick="register.php">
            Username: <input type="text" name="username">
            Password: <input type="password" name="password">
            Confirm Password: <input type="password" name="passconf">
            <input type="submit" value="Submit!">
        </form>
        <?php
        if (!empty($_POST)) {
            $password = $_POST['password'];
            $passconf = $_POST['passconf'];
            if ($pasword == $passconf) {
                $idFile = fopen("lib/id.txt", "r") or die("Error: Unable to open id file. Please try again. If this error persists, consult the Head Admin.");
                $id = fread($idFile, filesize("lib/id.txt"));
                $id = $id + 1;
                fclose($idFile);
                $idf2 = fopen("lib/id.txt", "r") or die("Error: Unable to open id file. Please try again. If this error persists, consult the Head Admin.");
                fwrite($idf2, $id);
                fclose($idf2);
                $userFile = fopen("lib/data/users.php", "a+") or die("Error: Unable to open users file. Please try again. If this error persists, consult the Head Admin");
                fwrite($userFile, '\n$users[' . $id . '] = array();\n' . '$users[' . $id . '][\'userRole\'] = AJAX_CHAT_USER;\n' . '$users[' . $id . '][\'userName\'] = \'' . $_POST['username'] . '\';\n' . '$users[' . $id . '][\'password\'] = \'' . $_POST['password'] . '\';\n' . '$users[\'' . $id . '\'][\'channels\'] = array(0,1);\n');
                echo "<br>Your user has been created. Click <a href=\"index.php\">here</a> to login.<br>";
            } else {
                echo "<br><span style=\"color:red;\">Your password does not match your confirmation of your pasword. Please try again.</span><br>";
            }
        }
        ?>
    </body>
</html>