Facebook Login Error: failed to open stream: HTTP request failed! HTTP/1.0 400 Bad Request

Question

I'm trying to follow the example to create a server side login to Facebook from here, but with no luck. In step 7, when I try to exchange the code with a token and store it in a session for later use, I always get this error :

  file_get_contents(): failed to open stream: HTTP request failed! HTTP/1.0 400 Bad Request

I know this already asked many times, but I still unable to solve this, as per this question, I tried using cURL, but it still does not work, it just returned false.

Other question told me to use the PHP SDK, but I don't know which method to use. So I'm completely lost in here.

---

Here's my code for calling the login form :

<a href="<?php echo LOGIN_URL; ?> ?>" class="btn btn-primary">Login with Facebook</a>

where LOGIN_URL is defined as :

define("LOGIN_URL", $facebook->getLoginUrl(array("redirect_uri" => APP_URL . "fb_login")));

in fb_login, I have this code :

$app->get("/fb_login", function() use($app, $facebook)
{
    $code = $_REQUEST["code"];

    $token_url = "https://graph.facebook.com/oauth/access_token?"
       . "client_id=" . APP_ID . "&redirect_uri=" . APP_URL . $_SESSION["request_uri"] // Previous URL
       . "&client_secret=" . APP_SECRET . "&code=" . $code;

    $response = file_get_contents($token_url); // Doesn't work
    $params = null;
    parse_str($response, $params);

    $_SESSION["access_token"] = $params["access_token"];

    // Let's try with cURL...
    // $ch = curl_init();
    // curl_setopt($ch, CURLOPT_URL, $token_url);
    // curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
    // $output = curl_exec($ch); // Returns false
    // curl_close($ch);

    $graph_url = "https://graph.facebook.com/me?access_token="
      . $params["access_token"];

    $user = json_decode(file_get_contents($graph_url));
    echo("Hello " . $user->name);

    var_dump($code); die();
});

Any help is appreciated. Thanks before.

Answer 1

To directly answer the question, the problem is most likely that you do not urlencode (make safe for URL transport) the redirect URL. The fastest fix will be:

$token_url = "https://graph.facebook.com/oauth/access_token?"
   . "client_id=" . APP_ID . "&redirect_uri=" . urlencode(APP_URL . $_SESSION["request_uri"])
   . "&client_secret=" . APP_SECRET . "&code=" . $code;

However, I would also suggest that you look at the Facebook SDK as this does this all for you.