Facebook PHP SDK V5和AJAX Graph API页面请求

I'm trying without success for 2 days now to retrieve page feed with Facebook PHP SDK. Details :

• I got a user, who is page admin
• I created an app (not public, is that a problem?)
• I use an AJAX called PHP script to try to retrieve feed, because I don't want to pollute main page loading.

All stuff given on PHP SDK doc is related to manual login and access token retrieval. I Managed to retrieve a user token using the 2-scripts code (login, and callback), with manage_pages speical grant require :

$fb = new Facebook\Facebook([
   'app_id' => $app_id,
   'app_secret' => $app_secret,
   'default_graph_version' => 'v2.2',
]);

$helper = $fb->getRedirectLoginHelper();

$permissions = ['manage_pages']; // Optional permissions
$loginUrl = $helper->getLoginUrl('http://domain.com/fb_callback.php',       $permissions);

How can achieve the same thing without manual redirection, is one script, in AJAX context? SHould I use Curl to emulate manual redirection?

THing which puzzle me out is that the same stuff tok 2 lines using JS framework :

window.fbAsyncInit = function() {
    // Framework init with Vinexpo app ID
    FB.init({
        appId      : '012345789',
        xfbml      : true,
        version    : 'v2.4'
    });

    // Check status
    FB.getLoginStatus(function(response) {
        if (response.status === 'connected') {

            // If connected, get last 2 posts on Facebook page
            FB.api(
                "/page_ID/posts?limit=2",
                {
                    access_token : response.authResponse.accessToken
                },
                function (responsePost) {
                    if (responsePost && !responsePost.error) {
                        // Fill tiles on social network panel

                    }
                }
            );
        }
    });

Thanks in advance for answers or leads.