MLPortClient merlionApiClient = new MLPortClient();
merlionApiClient.ClientCredentials.UserName.UserName = @"Имя_пользователя";
merlionApiClient.ClientCredentials.UserName.Password = @"Пароль";
merlionApiClient.helloWorld( "TEST" );

          serv = new MerlionIZ.MLPortClient();
          serv.ClientCredentials.UserName.UserName = login;
          serv.ClientCredentials.UserName.Password = pass;

WSHttpBinding myBinding = new WSHttpBinding();
myBinding.Security.Mode = SecurityMode.Transport;
myBinding.Security.Transport.ClientCredentialType = HttpClientCredentialType.Basic;

EndpointAddress ea = new EndpointAddress( @"https://apitest.merlion.com/dl/mlservice3?wsdl" );
MLPortClient merlionApiClient = new MLPortClient( myBinding, ea );

merlionApiClient.ClientCredentials.UserName.UserName = @"TC0051047|API";
merlionApiClient.ClientCredentials.UserName.Password = @"8yKP2BaWfo";
merlionApiClient.helloWorld( "TEST" );

<?php
$wsdl_url = "https://api.merlion.com/re/mlservice3?wsdl";
$params = array('login' => "ABC0123|MYLOGIN"
, 'password' => "LIzsldhf9"
, 'encoding' => "Windows-1251"
, 'features' => SOAP_SINGLE_ELEMENT_ARRAYS
);
try {
$client = new SoapClient($wsdl_url, $params);
$cat = $client->getCatalog('N1');
foreach ($cat->item as $row) {
echo $row->ID_PARENT." - ".$row->ID." - ".$row->Description."<br>";
}
} catch (SoapFault $E) {
echo $E->faultstring;
}
?>

WSHttpBinding binding = new WSHttpBinding();
binding.Security.Mode = SecurityMode.Transport;
binding.Security.Transport.ClientCredentialType = HttpClientCredentialType.Basic;
binding.MessageEncoding = WSMessageEncoding.Text;
binding.TextEncoding = Encoding.GetEncoding( "Windows-1251" );

EndpointAddress endpoint = new EndpointAddress( wsdlUri );

MLPortClient clientMerlionAPI = new MLPortClient( binding, endpoint );
clientMerlionAPI.ClientCredentials.UserName.UserName = login;
clientMerlionAPI.ClientCredentials.UserName.Password = password;
clientMerlionAPI.Open();

var topGroup = clientMerlionAPI.getCatalog( "Order" );

internal static readonly Encoding[] SupportedEncodings = new Encoding[] { Encoding.UTF8, Encoding.Unicode, Encoding.BigEndianUnicode };