SecureString from webservices to workflow in PHP

Hi, i need to pass a data type SecureString from PHP to execute a workflow, but the workflow receive as null, see the example below:

$i = 0;

$this->inParamsWorkFlow[$i]['name']  = 'user';

$this->inParamsWorkFlow[$i]['type']    = 'vCloud:User';

$this->inParamsWorkFlow[$i]['value']   = “dunes://service.dunes.ch/CustomSDKObject?id='d07da236c21a1ece50dfd2afcd47c74848c8d3d89476b389455c1a471bfcd70////https://xx.xxx.xx.xx/admin/user/d572427f-3c7f-4e9e-affe-2ff155092fa4'&dunesName='vCloud:User'”

$i++;

$this->inParamsWorkFlow[$i]['name']   = 'emailAddress';

$this->inParamsWorkFlow[$i]['type']     = 'string';

$this->inParamsWorkFlow[$i]['value']    = 'jorge@email.com';

$i++;

$this->inParamsWorkFlow[$i]['name']   = 'fullName';

$this->inParamsWorkFlow[$i]['type']     = 'string';

$this->inParamsWorkFlow[$i]['value']    = 'admin';

$i++;

$this->inParamsWorkFlow[$i]['name']   = 'password';

$this->inParamsWorkFlow[$i]['type']     = 'SecureString';

$this->inParamsWorkFlow[$i]['value']    = '123456';

$this->client                                       = new SoapClient('https://10.100.76.26:8281/vmware-vmo-webcontrol/webservice?WSDL');

$this->param                                      = array( 'username' => 'usuarioVCO', 'password' =>'xxxxxxx');

$this->param['workflowInputs']              = $this->inParamsWorkFlow;                                                  

$this->param['workflowId']                    = '21684088-9183-4b22-a002-ea7b38f0ff51';

$this->result                                       = $this->client->executeWorkflow($this->param);              

And this is the result in the workflow:

The parameter password is null.

What is the way to send a SecureString from webservices to workflow in PHP?

Thanks..!