This tutorial shows how to implement a "Continue with Facebook" button with just PHP. No JS required.

If you prefer to render the button with JS, see my other tutorial.

JS vs PHP rendering

This tutorial uses PHP to render the button. There are pros/cons compared to a JS version:

Cons:

• More coding;
• Vulnerable to future API "breaking changes"

Pros:

• It works on Firefox private mode;
• It works with "Facebook Container" plugin (it shows the button);

0. Create an app on FB’s developer

Go to

https://developers.facebook.com/apps (opens new window)

Create an app

Get the ID and SECRET

1. Install PHP SDK on your project folder

cd my-project
composer require facebook/graph-sdk

2. The code

Save this code on a file (ex. test-fb.php) run it on a server (ex. php -S localhost:3000) and open it in your browser.

The code is self-explanatory. But let me know in the comments if you think it is not.

<?php
/**
  * FB auth example - PHP SDK only
  * PHP SDK Install: composer require facebook/graph-sdk
  */
define('fbAppId', '1279821668858940');
define('fbAppSecret', '519da09587a63abd4318caf1fcea9d17');
define('fbVersion', 'v3.3');
define('thisUrl', 'http://localhost:3000/test-fb.php');

/* Load library */
require_once __DIR__ . '/vendor/autoload.php';

/* Sessions */
if (!session_id()) {
  session_start();
}

/* Init FB */
$fb = new \Facebook\Facebook([
  'app_id' => fbAppId,
  'app_secret' => fbAppSecret,
  'default_graph_version' => fbVersion
]);

/* Use the helper classes to get a Facebook\Authentication\AccessToken entity. */
$helper = $fb->getRedirectLoginHelper();

/* Has a token in cache. Check if valid */
if ($_SESSION['accessToken']) {
  $oauth = $fb->getOAuth2Client();
  $meta = $oauth->debugToken($_SESSION['accessToken']);
  $accessToken = $meta->getIsValid() ? $_SESSION['accessToken'] : null;
} else {
  /* Not in cache. Try to get a token based on GET arguments */
  $accessToken = $helper->getAccessToken();
}

/* Save token in cache for the next page load. getAccessToken() can only be used once per authorization */
$_SESSION['accessToken'] = (string) $accessToken;

/* Not signed in: show login button */
if (!$accessToken) {
  /* Generate Link */
  $permissions = ['email']; // Optional permissions
  $loginUrl = $helper->getLoginUrl(thisUrl, $permissions);
  echo '<a href="' . $loginUrl . '">Log in with Facebook!</a>';
}

/* Signed in: show user information */
else {
  /* Set token as default, for all communication */
  $fb->setDefaultAccessToken($accessToken);

  /* Get the \Facebook\GraphNodes\GraphUser object for the current user */
  $response = $fb->get('/me?fields=id,name,email');
  $me = $response->getGraphUser();

  /* Print info */
  echo "Logged in as {$me->getName()} ({$me->getEmail()})<br>";
  var_dump($response);
  var_dump($me);
}

Publishing

After testing, you need to publish your FB app: