Little class to handle Facebook API authentification with the PHP-SDK

facebook-auth.php

<?php
require './vendor/autoload.php';

use Facebook\Facebook;
use Facebook\Exceptions\FacebookResponseException;
use Facebook\Exceptions\FacebookSDKException;

define( 'FB_GROUP_APP_BASE_URL', 'https://wdj.ac' );
define( 'FB_GROUP_APP_CALLBACK_URL', FB_GROUP_APP_BASE_URL . '/facebook-auth.php?action=verify-user' );
define( 'FB_GROUP_APP_ID', '' );
define( 'FB_GROUP_APP_SECRET', '' );
define( 'FB_GROUP_APP_GRAPH_VERSION', 'v2.10' );
define( 'FB_GROUP_APP_PERMISSION_MANAGED_GROUPS', 'user_managed_groups' );
define( 'FB_GROUP_APP_PERMISSION_PUBLISH_ACTIONS', 'publish_actions' );
define( 'FB_GROUP_APP_ADD_NEW_USER_KEY', '' );
define( 'FB_GROUP_APP_TOKEN_FILENAME', './.fb-token' );

class FacebookAuth {

	private $fb;
	public $canvasHelper;
	public $loginHelper;
	public $oAuth2Client;

	public $permissions = [ FB_GROUP_APP_PERMISSION_MANAGED_GROUPS, FB_GROUP_APP_PERMISSION_PUBLISH_ACTIONS ];
	public $tokenFileName = FB_GROUP_APP_TOKEN_FILENAME;
	private $accessToken;
	private $validateNewUser;
	public $callbackURL = FB_GROUP_APP_CALLBACK_URL;

	public function __construct( $user = true, $validateNewUser = false, $appID = FB_GROUP_APP_ID, $appSecret = FB_GROUP_APP_SECRET, $graphVersion = FB_GROUP_APP_GRAPH_VERSION ) {

		$app                   = array(
			'app_id'                => $appID,
			'app_secret'            => $appSecret,
			'default_graph_version' => $graphVersion,
			//'persistent_data_handler' => 'memory' //session
		);
		$this->fb              = new Facebook( $app );
		$this->canvasHelper    = $this->fb->getCanvasHelper();
		$this->loginHelper     = $this->fb->getRedirectLoginHelper();
		$this->oAuth2Client    = $this->fb->getOAuth2Client();
		$this->validateNewUser = $validateNewUser;

		if ( ! $user ) {
			$this->addUser();
		} else {
			$this->initiate();
		}
	}

	/**
	 * File based:
	 * Initial logic to handle access token
	 */
	private function initiate() {
		try {
			// Get access token from file
			if ( file_exists( $this->tokenFileName ) && ! $this->validateNewUser ) {
				$token            = file_get_contents( $this->tokenFileName );
				$lastTokenRefresh = time() - filemtime( $this->tokenFileName );
				// Refresh token after 7 days (60 * 60 * 24 * 7)
				if ( $lastTokenRefresh > 604800 ) {
					$newToken = $this->refreshToken( $token );
					file_put_contents( $this->tokenFileName, (string) $newToken );
					$this->setAccessToken( (string) $newToken );
				} else {
					$this->setAccessToken( (string) $token );
				}
			} // If new user oAuth
			elseif ( file_exists( $this->tokenFileName ) && $this->validateNewUser ) {
				unlink( $this->tokenFileName );
				$this->setAccessToken( $this->loginHelper->getAccessToken() );
			} // Initial app start (never used before)
			else {
				$this->setAccessToken( $this->loginHelper->getAccessToken() );
				//$this->setAccessToken( $this->loginHelper->getAccessToken()->getValue() );
			}
		}
		catch ( FacebookResponseException $e ) {
			$this->exceptionHandler( $e->getMessage(), 'Facebook Graph returned an error:' );
		}
		catch ( FacebookSDKException $e ) {
			$this->exceptionHandler( $e->getMessage(), 'Facebook SDK returned an error:' );
		}

		if ( $this->getAccessToken() ) {
			if ( file_exists( $this->tokenFileName ) ) {
				$this->fb->setDefaultAccessToken( file_get_contents( $this->tokenFileName ) );
			} else {
				// OAuth 2.0 client handler
				// $oAuth2Client = $this->fb->getOAuth2Client();
				// Exchanges a short-lived access token for a long-lived one
				try {
					$longLivedAccessToken = $this->oAuth2Client->getLongLivedAccessToken( (string) $this->getAccessToken() );
					file_put_contents( $this->tokenFileName, (string) $longLivedAccessToken );
					$this->fb->setDefaultAccessToken( $longLivedAccessToken );
					$this->setAccessToken( $longLivedAccessToken );

				}
				catch ( FacebookSDKException $e ) {
					$this->exceptionHandler( $e->getMessage(), 'Facebook SDK returned an error:' );
				}
			}

			if ( $this->validateNewUser ) { //&& $this->getAccessToken()->isLongLived()
				$this->validateNewUser = false;
				echo "Succesfully connected!";
				echo "<script>window.setTimeout(function() { window.top.location.href='" . FB_GROUP_APP_BASE_URL . "'; }, 5000);</script>";
				exit;
			}
		} else {
			$this->exceptionHandler( 'No Facebook Connection!', 'Initiate error:' );
			exit();
		}
	}

	/**
	 * Start Facebook oAuth to connect new user
	 */
	public function addUser() {
		$loginUrl = $this->loginHelper->getLoginUrl( $this->callbackURL, $this->permissions );
		echo "<script>window.top.location.href='" . $loginUrl . "'</script>";
	}

	/**
	 * Refresh long-lived access token
	 * New since 2017-12-18
	 *
	 * @param $token
	 *
	 * @return \Facebook\Authentication\AccessToken
	 */
	public function refreshToken( $token ) {
		try {
			return $this->oAuth2Client->getAccessTokenFromCode(
				$this->oAuth2Client->getCodeFromLongLivedAccessToken(
					$token
				)
			);
		}
		catch ( FacebookSDKException $e ) {
			$this->exceptionHandler( $e->getMessage(), 'Facebook SDK returned an error:' );

			return $token;
		}
	}

	/**
	 * Validate the access token
	 *
	 * @return bool
	 */
	public function validate() {
		try {
			$request = $this->fb->get( '/me' );
		}
		catch ( FacebookResponseException $e ) {
			// When Graph returns an error

			if ( $e->getCode() == 190 ) {
				// When token is expired
				unlink( $this->tokenFileName );
				$this->exceptionHandler( 'Der Token ist abgelaufen!', 'Graph returned an error:' );

				return false;
			} else {
				// All other Graph errors
				$this->exceptionHandler( $e->getMessage(), 'Graph returned an error:' );

				return false;
			}
		}
		catch ( FacebookSDKException $e ) {
			// When validation fails or other local issues
			$this->exceptionHandler( $e->getMessage(), 'Facebook SDK returned an error:' );

			return false;
		}

		return true;
	}

}


/************************************
 * All the following is for directly calling the file
 ************************************/
$userAccessKey = FB_GROUP_APP_ADD_NEW_USER_KEY;   // Security access key for adding new connected user

// When action parameter is set and key is correct
if (
	( $action = filter_input( INPUT_GET, 'action', FILTER_SANITIZE_STRING ) ) &&
	( ( $key = filter_input( INPUT_GET, 'key', FILTER_SANITIZE_STRING ) ) && $key === $userAccessKey )
) {
	switch ( $action ) {
		// Start Facebook oAuth
		case 'add-user':
			$fb = new FBAutopost( 0 );
			break;
	}
} // When Facebook oAuth callback
elseif ( isset( $_GET['code'] ) && $action = filter_input( INPUT_GET, 'action', FILTER_SANITIZE_STRING ) && $action === 'verify-user' ) {
	$fb = new FBAutopost( 1, 1 );
}