Magento – No connection with Magento 1 SOAP API via https (SSL)

I try to get customer datas via a PHP script and the Magento 1 SOAP API. At my development system, every thing is works well.

But now when I try to use it at the online Shop with active SSL, I get no connections to the wsdl object.

My PHP call

$wsdl = 'https://urltoshop/api/v2_soap/index/?wsdl=1';
$user = 'soapuser';
$pass = 'paasword';
...
//options for ssl in php 5.6.5
$opts = array(
    'ssl' => array(
            'ciphers' => 'SHA-256',
            'verify_peer' => false,
            'verify_peer_name' => false
    )
);
// SOAP 1.2 client
$params = array(
    'encoding' => 'UTF-8',
    'verifypeer' => false,
    'verifyhost' => false,
    'soap_version' => SOAP_1_2,
    'trace' => 1,
    'exceptions' => 1,
    'connection_timeout' => 180,
    'stream_context' => stream_context_create($opts)
);
$proxy = new SoapClient($wsdl);
... 
try {
   $sessionId = $proxy->login($user, $pass);
} catch (Exception $e) {
   $sessionId = null;
   echo $e->getMessage();
}

And I get always the error message like this:

SoapFault: SOAP-ERROR: Parsing WSDL: Couldn't load from 'https://urltoshop/api/v2_soap/index/?wsdl=1' : failed to load external entity

This url works in a webbrowser, and I get the xml structure. I have already try a lot of SoapClient options like:

'verifyhost' => false, 
'verify_peer' => false, '
'verify_peer_name' => false 
 'ssl' => array('allow_self_signed' => true)); 

etc…

But nothing works for me.

Is this a problem with my PHP script, or a config problem in my Apache Webserver? Or something in the Magento configuration?

Has any of you guys any experience with such a constellation like this?

Does everyone know a good manual page, how to setup the SOAP API in Magento incl. a https:// connection?