top.location.href='" . $auth_url . "' No longer Works.

The following PHP example demonstrates how to access the signed_request parameter and prompt the user to authorize your app:

$app_id = "YOUR_APP_ID";

$canvas_page = "YOUR_CANVAS_PAGE_URL";

$auth_url = "http://www.facebook.com/dialog/oauth?client_id="

. $app_id . "&redirect_uri=" . urlencode($canvas_page);

$signed_request = $_REQUEST["signed_request"];

list($encoded_sig, $payload) = explode('.', $signed_request, 2);

$data = json_decode(base64_decode(strtr($payload, '-_', '+/')), true);

if (empty($data["user_id"])) {

echo("");

} else {

echo ("Welcome User: " . $data["user_id"]);

}

?>

The line in red which says:

echo("");

redirect your app to the authentication screen. This however no longer works. Replace the line with:

            echo "";