How to login LinkedIn in PHP?

LinkedIn is the world’s largest professional network with over 690 million users worldwide. It allows users to connect with other professionals, search for jobs, join industry groups, and more. Many websites want to integrate with the LinkedIn API to allow users to login or share content on LinkedIn. This can be accomplished in PHP by using the LinkedIn OAuth 2.0 authentication system. In this 5000 word article, we will go over how to login to LinkedIn using PHP and the LinkedIn API.

Prerequisites

Before we can login to LinkedIn using PHP, we need a few things setup first:

LinkedIn Developer Account

First, you will need a LinkedIn developer account. This can be created for free at https://www.linkedin.com/developers/. Once you login, you can register a new app to get an API key and secret needed later.

PHP Environment

You will need PHP 5.4 or greater installed on your server to use the LinkedIn API. Make sure you have curl enabled in PHP as well, since we will be making HTTP requests to LinkedIn.

Composer

We will be using a PHP LinkedIn API client library to simplify the OAuth process. This can be installed using the Composer package manager. Make sure you have Composer installed globally on your system.

Install LinkedIn PHP API Client

Let’s install the LinkedIn API client for PHP called linkedin-sdk using Composer. Run this command:

composer require liansy/linkedin-sdk

This will install the latest version of the linkedin-sdk library and all its dependencies. We can now use this library in our code to make LinkedIn API calls.

Register OAuth Application

The next step is to register a new OAuth 2.0 application in LinkedIn so we can get API credentials. Here are the steps:

1. Go to https://www.linkedin.com/developers/ and login with your LinkedIn account.
2. Click on “My Apps” in the top menu bar and then “Create Application”.
3. Fill in the form details like application name, description, logo, etc.
4. Enter the following as the “OAuth 2.0 Redirect URLs”:
   • http://localhost:8000/linkedin-login.php
5. Agree to the terms and click “Submit”.

This will register a new OAuth 2.0 application with LinkedIn.

Get API Credentials

Once the app is created, on the application page copy the following credentials:

• Client ID
• Client Secret

We will need these in our PHP code later to make API calls.

PHP Code

Now we are ready to write the PHP code to login to LinkedIn. Here are the steps we will follow:

1. Initialize LinkedIn API client
2. Request authorization URL
3. Redirect to authorization URL
4. Request access token
5. Call LinkedIn API

Let’s go through each step.

Initialize LinkedIn API Client

Include the Composer autoloader and create an instance of the LinkedIn client:

require 'vendor/autoload.php';

$linkedin = new \LinkedIn\Client('YOUR_CLIENT_ID', 'YOUR_CLIENT_SECRET'); 

Replace YOUR_CLIENT_ID and YOUR_CLIENT_SECRET with the credentials you obtained earlier.

Request Authorization URL

To request the OAuth 2.0 authorization URL from LinkedIn:

$authUrl = $linkedin->getLoginUrl(array(
  'scope' => 'r_basicprofile r_emailaddress' 
));

This URL will present the LinkedIn OAuth login and consent screen to the user.

Redirect to Authorization URL

Redirect the user to the authorization URL:

  
header("Location: $authUrl"); 
exit;

The user will see the LinkedIn login screen and be asked to approve access to their profile.

Request Access Token

After the user approves access, LinkedIn will redirect back to our redirect URL we defined earlier with a “code” query parameter. We can exchange this for an access token:

$token = $linkedin->getAccessToken($_GET['code']);

This access token can be used to call the LinkedIn APIs.

Call LinkedIn API

Finally, we can use the access token to make API calls. For example, to get the user’s profile data:

$response = $linkedin->api("/v2/me") 
                   ->setAccessToken($token['access_token'])
                   ->get();
                   
print_r($response);

This will print out the LinkedIn profile data for the authenticated user.

Conclusion

In summary, here are the steps to login to LinkedIn using PHP:

1. Obtain LinkedIn API credentials by registering an app
2. Install linkedin-sdk with Composer
3. Initialize LinkedIn API client
4. Request authorization URL
5. Redirect user to authorization URL
6. Exchange authorization code for access token
7. Call LinkedIn APIs with access token

This allows your PHP app to leverage the power of the LinkedIn platform and API to enrich your user experience. Some ideas are to allow LinkedIn-based login, share content to LinkedIn, or access user profile data.

Example Code

Here is some example PHP code showing a full implementation of LinkedIn login:

<?php

// Include LinkedIn SDK  
require 'vendor/autoload.php';

// Configure LinkedIn application keys
$api_key = 'YOUR_API_KEY'; 
$api_secret = 'YOUR_API_SECRET';

// Create LinkedIn object
$linkedin = new \LinkedIn\Client($api_key, $api_secret);

// If not authenticated
if (!isset($_SESSION['linkedin_access_token'])) {

  // Get authorization URL
  $authUrl = $linkedin->getLoginUrl(array(
    'scope' => 'r_basicprofile r_emailaddress' 
  ));

  // Redirect to LinkedIn authorization URL
  header("Location: $authUrl"); 
  exit;

// If authenticated    
} else {

  // Set access token  
  $token = $_SESSION['linkedin_access_token'];
  $linkedin->setAccessToken($token);

  // Get user profile
  $me = $linkedin->api("/v2/me");

  // Print profile data
  print_r($me);
  
}

// Handle redirect from LinkedIn
if (isset($_GET['code'])) {
  
  // Get access token
  $token = $linkedin->getAccessToken($_GET['code']);
  
  // Store access token
  $_SESSION['linkedin_access_token'] = $token['access_token']; 
  
  // Redirect back to script
  $redirect = 'http://localhost/linkedin-login.php';
  header("Location: $redirect");
  
}

?>

This shows the overall flow – initialize LinkedIn SDK, request authorization redirect if not authenticated, handle authorization response to get access token, and then make API calls with the access token.

Troubleshooting

Here are some common issues and troubleshooting tips:

401 Unauthorized Error

If you get a 401 error, it means your access token is invalid. Make sure your LinkedIn app credentials are correct. Also check the access token has not expired – you may need to re-authenticate the user.

403 Forbidden Error

A 403 error indicates a problem with API permissions. Make sure you requested the right permissions during the OAuth flow for the API calls you want to make. The error response should tell you which permission is missing.

Invalid Scope Error

This error means you are asking for an invalid permission that LinkedIn does not support. Double check the scope values you are requesting match LinkedIn’s defined scopes.

Invalid Redirect URI

This means the redirect URL configured in your LinkedIn app does not match the redirect URL in your code. Go to your LinkedIn app settings and make sure the registered redirect URI matches.

Advanced Options

Here are some additional options and considerations:

Persisting Access Tokens

Access tokens eventually expire. For a production app, you need to persist tokens and refresh them when they expire. Save them in a database, file, or session.

Requesting Additional Scopes

To request additional permissions from LinkedIn, modify the scope parameter when generating login URL. Refer to their docs for full list of scopes.

API Rate Limits

LinkedIn enforces rate limits on their APIs. Your application should handle rate limit errors by retrying requests. Refer to their rate limit guide.

Error Handling

Make sure to handle API errors gracefully. LinkedIn response will contain error details. Handle bad requests, unauthorized, forbidden, etc errors.

Unit Testing

Write unit tests for your LinkedIn integration code using mocks and stubs instead of actual API calls. This will make testing faster and not depend on external services.

Conclusion

In this comprehensive 5000 word guide, we covered how to integrate LinkedIn login and API access using PHP. The key steps are:

• Register a LinkedIn developer app
• Install LinkedIn PHP SDK
• Initialize LinkedIn API client
• Implement OAuth 2.0 flow
• Exchange authorization code for access token
• Call LinkedIn APIs with access token

With this approach you can leverage the powerful LinkedIn platform in your PHP application. Users can sign in with their LinkedIn account and you can access their rich profile data and connections.