WordPress class for registering users via Linkedin

a-theme-auth.php

<?php

function a_theme_auth_options_page()
{
    add_options_page( "A-Theme Auth options", "A-Theme Auth", "manage_options", "a-theme-auth", "a_theme_auth_options" );
}
add_action( 'admin_menu', 'a_theme_auth_options_page' );

function register_a_theme_auth_settings()
{
    register_setting( 'a_theme_auth_options_group', 'ath_auth_settings' );
}
add_action( 'admin_init', 'register_a_theme_auth_settings' );

function a_theme_auth_options()
{
    include( plugin_dir_path( __FILE__ ) . '/options-template.php' );
}

docs.md

#How does it work?

1. Read this - https://developer.linkedin.com/docs/oauth2
2. You send an API GET call to get the authorization code.
3. With the authorization code you send a POST call to get the access token.
4. With the access token you send a GET call to get the users data. Simple right?

You will probably need to tweak it to your needs, but this is a good starting point. The socialite class has all the methods that interacts with Linkedin.

linkedin-callback.php

<?php

function ath_linkedin_authentication()
{
    $socialite = new Socialite();
    //After this all will be handled by ath_linkedin_callback function. 
    $socialite->get_authorization_code();
}

function ath_linkedin_callback()
{
    $socialite = new Socialite();

    $homepage = network_site_url( '/' );

    $code  = $_GET['code'];
    $state = $_GET['state'];

    if( $socialite->state == $state )
    {
        $access_token = $socialite->get_access_token( $code );
    }

    if( $access_token )
    {
        $users_data = $socialite->get_users_data( $access_token );
    }

    $email         = $users_data->emailAddress;
    $profile_image = $users_data->pictureUrl;
    $first_name    = $users_data->firstName;
    $last_name     = $users_data->lastName;
    $username      = $users_data->firstName." ".$users_data->lastName;


    //If user exists we will simply log him in.
    $user = get_user_by( "email", $email );

    if( ! empty( $user ) )
    {
        wp_clear_auth_cookie();
        wp_set_current_user ( $user->ID );
        wp_set_auth_cookie  ( $user->ID, true );

        $_SESSION["home_success"] = "Welcome back $user->user_login!";
        wp_redirect( $homepage );
        exit;
    }

    $user_data = array(
        'user_login' =>  $username,
        'user_email' =>  $email,
        'user_pass'  =>  ""
    );

    $user_id = wp_insert_user( $user_data );

    if( is_wp_error( $user_id ) )
    {
        $_SESSION["errors"]["register_error_url"] = "Sorry, registration failed due to an unxpected error. We are working on fixing it as soon as possible.";
        wp_safe_redirect( $register_url );
        exit;
    }

    add_user_meta( $user_id, "profile_image", $profile_image );
    add_user_meta( $user_id, "provider", "linkedin" );

    //Login the user.
    wp_clear_auth_cookie();
    wp_set_current_user ( $user_id );
    wp_set_auth_cookie  ( $user_id, true );

    $_SESSION["home_success"] = "Welcome $username, you have registered successfully.";
    wp_safe_redirect( $homepage );
    exit;


}

login.php

<!-- 
An example of how the login/register buttin might look. The action and the hidden input are the most important parts. 
-->
<form class="form-horizontal" action="<?php echo get_admin_url() ?>admin-post.php">
    <div class="form-group">
        <input type='hidden' name='action' value='linkedin_authentication' />
        <button class="btn btn-block btn-social btn-linkedin" type="submit">
            <i class="fa fa-linkedin"></i> Sign in with Linkedin
        </button>
    </div>
</form>

main-file.php

<?php

define( 'ATH_AUTH_PATH', plugin_dir_path( __FILE__ ) );

include( ATH_AUTH_PATH . 'includes/options/a-theme-auth.php' );
include( ATH_AUTH_PATH . 'includes/socialite/socialite-class.php' );
include( ATH_AUTH_PATH . 'includes/socialite/callbacks/linkedin-callback.php' );

//For the linkedin button that the user will click
add_action('admin_post_nopriv_linkedin_authentication', 'ath_linkedin_authentication');
//For the callback URL
add_action('admin_post_nopriv_linkedin_callback', 'ath_linkedin_callback');

options-template.php

<div class="wrap">
<h1>A-Theme Auth settings page</h1>

<form method="post" action="options.php">

<?php settings_fields( 'a_theme_auth_options_group' ); ?>
<?php do_settings_sections( 'a_theme_auth_options_group' ); ?>
<?php
    $options = get_option( 'ath_auth_settings' );
?>

<table class="form-table">

    <tr valign="top">
        <th scope="row">Linkedin client id</th>
        <td>
            <?php $linkedin_client_id = ( isset( $options['linkedin_client_id'] ) ) ? "*******".substr( $options['linkedin_client_id'], -4 ) : ""; ?>
            <input class="regular-text" type="text" name="ath_auth_settings[linkedin_client_id]" value="<?php echo $linkedin_client_id; ?>"/>
        </td>
    </tr>

     <tr valign="top">
         <th scope="row">Linkedin client secret</th>
         <td>
             <?php $linkedin_client_secret = ( isset( $options['linkedin_client_secret'] ) ) ? "*******".substr( $options['linkedin_client_secret'], -4 ) : ""; ?>
             <input class="regular-text" type="text" name="ath_auth_settings[linkedin_client_secret]" value="<?php echo $linkedin_client_secret; ?>"/>
         </td>
     </tr>

 </table>

<?php submit_button(); ?>
</form>
</div>

socialite.php

<?php

class Socialite
{
    private $linkedin_client_id;
    private $linkedin_client_secret;
    private $redirect_uri           = "http://localhost:3000/water/wp-admin/admin-post.php?action=linkedin_callback";
    private $linkedin_scope         = "r_basicprofile r_emailaddress";
    private $linkedin_auth_uri      = "https://www.linkedin.com/oauth/v2/authorization";
    private $linkedin_token_uri     = "https://www.linkedin.com/oauth/v2/accessToken";
    private $linkedin_people_uri    = "https://api.linkedin.com/v1/people/";
    public  $state                  = "bhjbbcjheghjbcvjhcbbjcjnsfece";

    public function __construct()
    {
        $options                      = get_option( 'ath_auth_settings' );
        $this->linkedin_client_id     = ( isset( $options['linkedin_client_id'] ) ) ? $options['linkedin_client_id'] : "";
        $this->linkedin_client_secret = ( isset( $options['linkedin_client_secret'] ) ) ? $options['linkedin_client_secret'] : "";
    }

    public function get_authorization_code()
    {
        $curl = curl_init( $this->linkedin_auth_uri."?".http_build_query( array(
                "response_type" => "code",
                "client_id"     => $this->linkedin_client_id,
                "redirect_uri"  => $this->redirect_uri,
                "state"         => $this->state,
                "scope"         => $this->linkedin_scope
            ) )
        );

        $response = curl_exec( $curl );
        $info     = curl_getinfo( $curl );
        curl_close( $curl );
        wp_redirect( $info['redirect_url'] );

    }

    public function get_access_token( $code )
    {
        $curl = curl_init();
        curl_setopt_array($curl, array(
                    CURLOPT_HTTPHEADER => array('Content-Type: application/x-www-form-urlencoded'),
                    CURLOPT_RETURNTRANSFER => 1,
                    CURLOPT_URL => $this->linkedin_token_uri,
                    CURLOPT_POST => 1,
                    CURLOPT_POSTFIELDS => http_build_query ( array(
                        "client_id" => $this->linkedin_client_id,
                        "client_secret" => $this->linkedin_client_secret,
                        "grant_type" => "authorization_code",
                        "redirect_uri" => $this->redirect_uri,
                        "code" => $code
                    )),
                ));

        $response = json_decode( curl_exec( $curl ) );
        $info     = curl_getinfo( $curl );
        if( $info['http_code'] != 200 )
        {
            return false;
        }
        curl_close( $curl );
        return $response->access_token;
    }

    public function get_users_data( $access_token )
    {
        $curl = curl_init();
        $login_url = network_site_url( '/login' );

        curl_setopt_array($curl, array(
            CURLOPT_HTTPHEADER => array( 'Authorization: Bearer'.$access_token ),
            CURLOPT_RETURNTRANSFER => 1,
            CURLOPT_URL => $this->linkedin_people_uri.'~:(email-address,first-name,last-name,picture-url)?format=json'
        ));
        $response = json_decode( curl_exec( $curl ) );
        $info     = curl_getinfo( $curl );
        curl_close( $curl );
        if( $info['http_code'] == 401 )
        {
            $_SESSION["errors"]["login_error_url"] = "Something went wrong. Please try again or contact us.";
            wp_redirect( $login_url );
            exit;
        }
        return $response;
    }
}