$client = new Zend_Http_Client('https://www.example.com/', array(
'adapter' => 'Zend_Http_Client_Adapter_Proxy',
'proxy_host' => 'proxy.shr.secureserver.net',
'proxy_port' => 3128
));
$sessionToken = Zend_Gdata_AuthSub::getAuthSubSessionToken($singleUseToken, $client);
This can also be used with ClientLogin:
$clientLoginClient = Zend_Gdata_ClientLogin::getHttpClient($email, $passwd, 'cl', $client);