Added support for multiple chained proxies that append a comma and their hostnames to the previous X-Forwarded-Host header.

    If we have Client <---> Fwd Proxy1 (first.proxy) <---> Fwd Proxy2 (second.proxy )<---> Application (third.server), then we
    will have these values for a script executed on third.server::

    $_SERVER['HTTP_X_FORWARDED_HOST'] = 'first.proxy, second.proxy';
    $_SERVER['HTTP_HOST'] = 'third.server';

    If we use the raw value from $_SERVER['HTTP_X_FORWARDED_HOST'] for composing return URLs, we will generate invalid return URLs,
    in our case 'http://first.proxy, second.proxy/fb_oauth.php', and get a 'Oauth exception 191' or some other error message.

    If we properly process the X-Forwarded-Host value by taking the leftmost host, we will not get errors.

Author: moisadoru

src/base_facebook.php

@@ -1156,7 +1156,7 @@ protected function getUrl($name, $path='', $params=array()) {
 
   protected function getHttpHost() {
     if ($this->trustForwarded && isset($_SERVER['HTTP_X_FORWARDED_HOST'])) {
-      return $_SERVER['HTTP_X_FORWARDED_HOST'];
+      return strtok($_SERVER['HTTP_X_FORWARDED_HOST'], ',');
     }
     return $_SERVER['HTTP_HOST'];
   }