I'm trying to find the answer why WCF-BasicHttp, WCF-WSHttp based Receive Locations or Send ports do not allow null or empty string for Service Certificate prop (if choose Transport type security with certificate)?
Is it a bug or there a way to do it.
As per MS doc its default value is empty string. How to Configure a WCF-WSHttp Send Port
I have only once SSL cert that I have to use as Client.
That's because when you select Transport type security with certificate you are telling it to use certificates to both authenticate yourself and the server you are connecting too.
You should be able to obtain the certificate you need for the Service Certificate just by browsing to the web service and then using the browser to copy the certificate to a file and then installing it into the Other People store in the Local Machine location and putting the Thumbprint into the ServiceCertificate setting. If that does not work, as the owners of the service to send you the public cert. In fact to use the service with client certificate authentication, you will most likely have to send your public certificate to the owner of the web service.
If the service does not have a SSL/TSL certificate then you cannot use it with security Transport as the transport layer is not secure.