Linkedin 401 [Unauthorized] Invalid or Expired Tokens Error

I have a requirement to authenticate my site with Linkedin. I am using the following code to connect to an access token. I can see from the linked links doc the token validity is 60 days. Everything works for me getting access token, I can see "expires_in" as 5183999 seconds id (60 days).

My problem is when I request userinfo with this token after 2 days, I get a 401 error. The lifetime of the access token is unstable. I searched a lot for the 401 error, read, so there may be links, but not getting the exact answer. Why are you getting this 401 error?

Please help me to solve this problem. Your help is greatly appreciated.

{ 
        errorCode: 0,
        message: '[unauthorized] Invalid or expired token.',
        requestId: 'P7IR3JY3GZ',
        status: 401,
        timestamp: 1410937984755 
} 

      

        
        
        
      

    

// PHP code to 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);
    }