Support Authorization header passed as ENV var

Some hosts (at this point I only know of Fortrabbit) require Authorization headers to be passed as an environment variable, which PHP will then shove into . See more: http://fortrabbit.com/docs/essentials/quirks-and-constraints\#authorization-header

src/League/OAuth2/Server/Resource.php

@@ -244,7 +244,15 @@ class Resource
      */
     protected function determineAccessToken($headersOnly = false)
     {
-        if ($header = $this->getRequest()->header('Authorization')) {
+        // Try to get it directly from a header
+        if (! $header = $this->getRequest()->header('Authorization')) {
+
+            // Failing that try getting it from a server variable
+            $header = $this->getRequest()->server('HTTP_AUTHORIZATION');
+        }
+
+        // One of them worked
+        if ($header) {
             // Check for special case, because cURL sometimes does an
             // internal second request and doubles the authorization header,
             // which always resulted in an error.
@@ -269,5 +277,4 @@ class Resource
 
         return $accessToken;
     }
-
 }