$auth_sql = mysql_query("SELECT salt, password, username FROM users WHERE username='$username'") or die("Error, checking salt");

        $auth_row = mysql_fetch_array($auth_sql)
            $db_salt = $auth_row['salt'];
            $db_username = $auth_row['username'];
            $db_password = $auth_row['password'];

            if($db_username === $username){
                $password = sha1($password.$db_salt);
            }