cXML Invoicing

Hi 

I am trying to set up cXML invoicing in PeopleSoft. While I have been able to successfully send cXML invoice through sendmaster, I would like to understand how I can expose the webservice to internet so that vendors can send the invoices directly to that link. Has someone exposed such a service externally to internet? Does it require any customization? How do I authenticate that the sender is a valid user / organization that should be posting invoices to my URL?

Thanks in advance

Regards

Srinivasan