After countless hours, I finally managed to figure it out!
You have to call the getHttpClient()
on the REST object, and then call the function you need that's normally in the Zend_Http_Client()
after that.
Here's a quick example:
$client = new Zend_Rest_Client($base_url);
$client->getHttpClient()->setAuth($username, $password, Zend_Http_Client::AUTH_BASIC);
...
Hopefully this can help others who encounter the same problem eventually.