Session variable loses value after redirection - php

Question

I have three files.
File 1: index.php
which redirects to second.php and sends id=$var to second.php.
code:
$var=52013;
window.open('second.php?id=$var','name','width=1000,height=700,scrollbars=yes');
File 2: second.php
In this file I have received $var, when I print it in logs it displays value of $var.
<?php
session_start();
$_SESSION['id'] = $_REQUEST['id'];
$GLOBALS["log"]->fatal("Get id of order = ".$_SESSION['id']);
//Here it redirects to third file for some varification online.
//This condition is true first time when this page is called but after
//redirection from third.php this condition becomes false.So code below
//this if statement will be executed after redirection from third file.
if(condition==true)
{
header("Location: http://third.php");
}
print "Please visit:\n$authUrl\n\n";
print "Please enter the auth code:\n";
//After redirection from third.php i want to write document using value stored
//in session variable which we get at top.($_SESSION['id'])
$val = $_SESSION['id'];
//Write a file
$file_open = fopen("modules/doc/views/document.txt","wb");
$content = $val;
fwrite($file_open,$content);
fclose($file_open);
File 3: Third.php
This file do some varification online and then redirect to second.php in order to write session id in document.txt
So the problem is that when third.php redirects to second.php file the session variable loses its value. I want to write the value of session variable in document.txt after redirection from third.php but at that time $_SESSION['id'] contains nothing.
But the process should be same, I don't want to change it. It's the requirement.
i.e index.php -> second.php -> third.php -> second.php -> write session value.
Thanks

Answer 1

at the begining of the second.php you do this:
session_start();
$_SESSION['id'] = $_REQUEST['id'];
which is clears the session, and puts into $_SESSION['id'] whatever was received in $_REQUEST['id']. That is why you have nothing in $_SESSION['id'] when commint from third.php. Note that when you do this:
window.open('second.php?id=$var' ...
you just send string '$var' in id