Feature/merge 3 0 develop (#298)

* merging 3.0 into develop

* N°5102 - Allow to send emails (eg. notifications) using GSuite SMTP and OAuth
* migration to iTop 3.1

Co-authored-by: Eric Espie <eric.espie@combodo.com>

lib/league/oauth2-google/examples/index.php

@@ -0,0 +1,35 @@
+<?php
+
+$provider = require __DIR__ . '/provider.php';
+
+if (!empty($_GET['error'])) {
+
+    // Got an error, probably user denied access
+    exit('Got error: ' . htmlspecialchars($_GET['error'], ENT_QUOTES, 'UTF-8'));
+
+} elseif (empty($_GET['code'])) {
+
+    // If we don't have an authorization code then get one
+    $authUrl = $provider->getAuthorizationUrl();
+    $_SESSION['oauth2state'] = $provider->getState(); 
+    header('Location: ' . $authUrl);
+    exit;
+
+} elseif (empty($_GET['state']) || ($_GET['state'] !== $_SESSION['oauth2state'])) {
+
+    // State is invalid, possible CSRF attack in progress
+    unset($_SESSION['oauth2state']);
+    exit('Invalid state');
+
+} else {
+
+    // Try to get an access token (using the authorization code grant)
+    $token = $provider->getAccessToken('authorization_code', [
+        'code' => $_GET['code']
+    ]);
+
+    $_SESSION['token'] = serialize($token);
+
+    // Optional: Now you have a token you can look up a users profile data
+    header('Location: /user.php');
+}