//Exemplo 3 com negotiate
$username ='xxxx';
$password = 'xxxx';
$url = 'http://suapaginadeapi.com.br/api';
$client = new Zend_Http_Client($url);
$client->setHeaders('WWW-Authenticate', 'Negotiate');
$client->setAuth($username, $password, Zend_Http_Client::AUTH_BASIC);
$response = $client->request('GET');
print_r($response->getBody());