WCF服务返回空认证信息问题求助：Basic调用异常排查

我正在修复一个此前正常运行的WCF服务，尝试使用Basic认证调用时，收到的服务响应中支持的认证头为空字符串。我怀疑客户修改了支持的认证方式，但多次询问项目相关人员仍无法获知具体支持的认证类型。

异常情况 #

正常情况下，服务会标注支持的认证头为Basic或其他类型，但当前返回的支持认证头为空字符串。

调用代码 #

// Create the binding.
var myBinding = new BasicHttpBinding()
{
    ReceiveTimeout = new TimeSpan(0, 20, 0),
    MaxReceivedMessageSize = 1000000000,
    Security =
    {
        Mode = BasicHttpSecurityMode.TransportCredentialOnly,
        Transport =
        {
            ClientCredentialType = HttpClientCredentialType.Basic, 
            ProxyCredentialType = HttpProxyCredentialType.Basic
        },
    }
};

var ea = new
    EndpointAddress(ConnectionStringOptions.SAPMEMaterialListEndPoint);

var materialList = (List<MaterialListItem>)await FetchDataPersistently(async () =>
{
    // Create the client.
    var cc = new XacuteWSSoapClient(myBinding, ea);
    // The client must provide a user name and password. The code
    // to return the user name and password is not shown here. Use
    // a database to store the user name and passwords, or use the
    // ASP.NET Membership provider database.
    cc.ClientCredentials.UserName.UserName = ConnectionStringOptions.OneERPUser;
    cc.ClientCredentials.UserName.Password = ConnectionStringOptions.OneERPPassword;

    var response = await cc.XacuteAsync(ConnectionStringOptions.OneERPUser,
    ConnectionStringOptions.OneERPPassword, new InputParams
    {
        Site = ConnectionStringOptions.OneERPSite
    });
});

疑问 #

服务返回空字符串的具体含义是什么？是配置错误还是隐含某种未明确的信息？

内容的提问来源于stack exchange，提问作者Zifnab