try {
    $opts = array(
        'http' => array(
            'user_agent' => 'PHPSoapClient'
        )
    );
    $context = stream_context_create($opts);
 
    $wsdlUrl = 'https://www.n11faturam.com/integrationservicewithoutmtom/IntegrationService.asmx?WSDL';
    $client = new SoapClient($wsdlUrl, array(
        'trace' => 1,
        'cache_wsdl' => WSDL_CACHE_NONE,
        'stream_context' => stream_context_create(array(
            'ssl' => array(
            'ciphers'=>'AES256-SHA', // eklediğim kısım burası
                'verify_peer' => false,
                'verify_peer_name' => false,
                'allow_self_signed' => true
            )
        ))
     ));
 
        $CorporateCode = 'xxx';
        $LoginName = 'xxx';
        $Password = 'xxx';
 
    $result = $client->GetFormsAuthenticationTicket($CorporateCode,$LoginName,$Password);
    print_r($result);
}
catch(Exception $e) {
    echo $e->getMessage();