表用户名和密码的验证建议

Question

Please take a look at this code. this is a restricted area where individuals can edit their details. at the moment I dont want individuals to edit username and password. is there any implementation to protect (validate) those fields but the details should still being displayed at the text box.

public function blabla($lllll)
{
    try {
        $con = new PDO( DB_DSN, DB_USERNAME, DB_PASSWORD );
        $con->setAttribute( PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION );
        $book = "SELECT * FROM x WHERE id =".$usr;
        $stmt = $con->prepare($book);
        $stmt->execute();
        $get = $stmt->fetch(PDO::FETCH_ASSOC);
        $ts = new Account;
        echo("<div id='box'>
        <div class='box-header'>". $get['']."</div>
        <div class='box-content'>
        <form method='post'>
        <table width='50%'>
        <tr>
            <td>Name:</td>
            <td><input type='text' size='0' name='name' value='".$get['name']."'  /></td>
        </tr>
        <tr>
            <td>Surname:</td>
            <td><input type='text' size='0' name='surname' value='".$get['surname']."'  /></td>
        </tr>
        <tr>
            <td>Username:</td>
            <td><input type='text' size='0' name='username' value='".$get['username']."'  /></td>
        </tr>
        <tr>
            <td>Password:</td>
            <td><input type='text' size='0' name='password' value='".$get['password']."'  /></td>
        </tr>
        <tr>
            <td>E-mail:</td>
            <td><input type='text' size='0' name='email' value='".$get['email']."'  /></td>
        </tr>
        ");
        echo("</table></form></div></div>");
    }catch( PDOException $e ) {
        return $e->getMessage();
    }
}