Follow the below steps in order to use the linkedin API.

• Go to the Apps page at LinkedIn Developer Network and login with your LinkedIn account credentials https://www.linkedin.com/secure/developer

• Click on the Add New Application link for create new App

• Enter the new application details into the app registration form.

After successfully registered you will get the linkedin API key and Secret Key .

You have to download Twitter OAUTH library which can available very easily in Git hub. You will get below files ,

• class.linkedClass.php // Class Get user Information
• config.php // Configuration file
• linkedinoAuth.php // Call methods
• OAuth.php // Twitter OAUTH library

Edit config.php

<?php

$config['base_url']             =   'http://demo.phpgang.com/'; 
$config['callback_url']         =   'http://demo.phpgang.com/index.php';
//linkedin configuration
$config['linkedin_access']      =   'your_linkedin_access';
$config['linkedin_secret']      =   'your_linkedin_secret'; 
$config['linkedin_library_path']=   'linkedinoAuth.php';
?>

Index.php

Shows a button for linkedin authorization if not authorized.

Redirect you to linkedin.php generate token and redirect to linkedin app authorization page.

<?php
    session_start();
    include_once 'oAuth/config.php';
    include_once 'oAuth/linkedinoAuth.php';

    # First step is to initialize with your consumer key and secret. We'll use an out-of-band oauth_callback
    $linkedin = new LinkedIn($config['linkedin_access'], $config['linkedin_secret'], $config['base_url'] . 'linkedin_login_oauth/linkedinauth.php' );
//    $linkedin->debug = true;

    # Now we retrieve a request token. It will be set as $linkedin->request_token
    $linkedin->getRequestToken();
    $_SESSION['requestToken'] = serialize($linkedin->request_token);

    # With a request token in hand, we can generate an authorization URL, which we'll direct the user to
   ## echo "Authorization URL: " . $linkedin->generateAuthorizeUrl() . "\n\n";
    header("Location: " . $linkedin->generateAuthorizeUrl());
?>

Once you Allow access it will redirect you on linkedinauth.php (defined in linkedin.php) and show all data of authorized user.