aşağıdaki şekilde deneyiniz

$client = new SoapClient('http://data.altinkaynak.com/DataService.asmx?WSDL');  

$auth = new stdClass();  
$auth->Username = 'AltinkaynakWebServis';  
$auth->Password = 'AltinkaynakWebServis';  

$header = new SoapHeader('http://data.altinkaynak.com/', 'AuthHeader', $auth, false);  
$client->__setSoapHeaders($header);  

$response = $client->GetCurrency();  

$xml = simplexml_load_string($response->GetCurrencyResult);  

$dolar = $xml->Kur[0]->Satis; 
$euro = $xml->Kur[1]->Satis; 


settype($euro, "string"); 
settype($dolar, "string");

if($_POST['dolar']):
$dolar = $_POST['dolar'];
$euro = $_POST['euro'];
endif;