Hi,
I know this option is not the most clean, but in my case it works.
In the method makeRequest of the file lib/google/lib/curlio.php, I had to add
....
global $CFG;
.....
// Parse out the raw response into usable bits.
list($responseHeaders, $responseBody) = self::parseHttpResponse($respdata, $respheadersize);
if (!empty($CFG->proxyhost)) {
list($responseHeaders, $responseBody) = self::parseHttpResponse($responseBody,0);
}
....
I hope it is useful.