Linkedin 401 [unauthorized] Invalid or expired token error - php

Question

I have a requirement to authenticate my site with Linkedin. Am using following code to get linkedin Access token. I can see from the linkedin docs the validity of token is 60 days. Everything works for me am getting access token, i can see the "expires_in" as 5183999 seconds id (60 days).
My problem is when i request for userinfo using this token after 2 days, am getting a error 401 response. The access token lifetime is not stable. I have searched a lot for 401 error, read so may links but not get the exact answer. Why am getting this 401 error ?
Please help me to solve this issue. Your help is much appreciated.
{
errorCode: 0,
message: '[unauthorized] Invalid or expired token.',
requestId: 'P7IR3JY3GZ',
status: 401,
timestamp: 1410937984755
}
// PHP CODE TO GET ACCESS TOKEN
<?php
// Change these
require "config.php";
//define('API_KEY', $ );
//define('API_SECRET', 'secret' );
//define('REDIRECT_URI', 'redirecturl');//http://' . $_SERVER['SERVER_NAME'] . $_SERVER['SCRIPT_NAME']);
define('SCOPE', 'w_messages rw_company_admin r_fullprofile r_emailaddress rw_nus r_network rw_company_admin rw_groups' );
// You'll probably use a database
session_name('linkedin');
session_start();
// OAuth 2 Control Flow
if (isset($_GET['error'])) {
// LinkedIn returned an error
print $_GET['error'] . ': ' . $_GET['error_description'];
exit;
} elseif (isset($_GET['code'])) {
// User authorized your application
if ($_SESSION['state'] == $_GET['state']) {
print_r("ssssssssssssssssssssssssssssssssssssssss");
// Get token so you can make API calls
getAccessToken();
} else {
// CSRF attack? Or did you mix up your states?
exit;
}
} else {
if ((empty($_SESSION['expires_at'])) || (time() > $_SESSION['expires_at'])) {
// Token has expired, clear the state
$_SESSION = array();
}
if (empty($_SESSION['access_token'])) {
// Start authorization process
print_r("ddddddddddddddddddddd");
getAuthorizationCode();
}
}
// Congratulations! You have a valid token. Now fetch your profile
$user = fetch('GET', '/v1/people/~:(id,first-name,last-name,picture-url)');
$pages = fetch2('GET', '/v1/companies:(id,name,logo-url)');
$user->pages = $pages;
$user->accesstoken = $_SESSION['access_token'];
echo "expiry time". $_SESSION['expires_in'];
print_r($pages);
print_r($user);
$SCRIPT = '<script>window.opener.postMessage('.json_encode($user) .',"*");</script>';
session_name('linkedin') ;
session_unset();
echo $SCRIPT;
echo '<h1>', HtmlSpecialChars($user->firstName),
' you have logged in successfully with LinkedIn!</h1>';
echo '<pre>', HtmlSpecialChars(print_r($user, 1)), '</pre>';
//print "Hello $user->firstName $user->lastName.";
exit;
function getAuthorizationCode() {
$params = array('response_type' => 'code',
'client_id' => API_KEY,
'scope' => SCOPE,
'state' => uniqid('', true), // unique long string
'redirect_uri' => REDIRECT_URI,
);
// Authentication request
$url = 'https://www.linkedin.com/uas/oauth2/authorization?' . http_build_query($params);
// Needed to identify request when it returns to us
$_SESSION['state'] = $params['state'];
// Redirect user to authenticate
header("Location: $url");
exit;
}
function getAccessToken() {
$params = array('grant_type' => 'authorization_code',
'client_id' => API_KEY,
'client_secret' => API_SECRET,
'code' => $_GET['code'],
'redirect_uri' => REDIRECT_URI,
);
// Access Token request
$url = 'https://www.linkedin.com/uas/oauth2/accessToken?' . http_build_query($params);
// Tell streams to make a POST request
$context = stream_context_create(
array('http' =>
array('method' => 'POST',
)
)
);
// Retrieve access token information
$response = file_get_contents($url, false, $context);
// Native PHP object, please
$token = json_decode($response);
// Store access token and expiration time
$_SESSION['access_token'] = $token->access_token; // guard this!
$_SESSION['expires_in'] = $token->expires_in; // relative time (in seconds)
$_SESSION['expires_at'] = time() + $_SESSION['expires_in']; // absolute time
return true;
}
function fetch($method, $resource, $body = '') {
$params = array('oauth2_access_token' => $_SESSION['access_token'],
'format' => 'json',
);
// Need to use HTTPS
$url = 'https://api.linkedin.com' . $resource . '?' . http_build_query($params);
// Tell streams to make a (GET, POST, PUT, or DELETE) request
$context = stream_context_create(
array('http' =>
array('method' => $method,
)
)
);
// Hocus Pocus
$response = file_get_contents($url, false, $context);
// Native PHP object, please
return json_decode($response);
}
function fetch2($method, $resource, $body = '') {
$params = array('is-company-admin'=>'true','format' => 'json','oauth2_access_token' => $_SESSION['access_token'],
);
// Need to use HTTPS
$url = 'https://api.linkedin.com' . $resource . '?' . http_build_query($params);
// Tell streams to make a (GET, POST, PUT, or DELETE) request
$context = stream_context_create(
array('http' =>
array('method' => $method,
)
)
);
// Hocus Pocus
$response = file_get_contents($url, false, $context);
// Native PHP object, please
return json_decode($response);
}