php中，怎么通过soap传递两个参数，（ms-security下）

$xml = '
            
            
            admin
            PasswordText
            
            ';

        $header = new SoapHeader('http://docs.oasis-open.org/wss/2004/01/oasis-200401-wss-wssecurity-secext-1.0.xsd', 'CallbackHandler', new SoapVar($xml, XSD_ANYXML), TRUE);

        $this->client = new SoapClient($wsdl);
        $this->client->__setSoapHeaders(array($header));

        $userInfo = turnObjectToArray($this->client->__call('checkUser', array('username' => array('username' => 'username', 'password' => 'password'))));

SoapFault exception: [soap:Server] Fault occurred while processing. in 

$info = turnObjectToArray($this->client->__call('getClasses', array('gradeId' => array('gradeId' => $data['id']))));