The Web Services Stack defines an architecture in which SOAP over HTTP(S) is used as the transport layer protocol. As well, custom web services can be plugged into it. All web services in OpenSSO Enterprise (whether proprietary or custom) are front-ended by a servlet endpoint called the SOAPReceiver. The SOAPReceiver validates digital signatures or encryptions from incoming SOAP request messages and authenticates the remote web services client. From a high-level, a user requests a specific service which passes the request to the SOAPReceiver which, in turn, passes it to the Liberty Personal Profile Service (or a custom web service). Figure 12–2 illustrates the architecture of the Web Services Stack and how a web service client (WSC) communicates with the web service provider (WSP).