1. A method for maintaining service correlation within a network service access gateway, said method comprising: receiving a first service invocation into the service access gateway executing on one or more microprocessors, wherein said first service invocation includes a first service correlation identifier contained in a first request context; retrieving the first service correlation identifier from the first request context and storing said first service correlation identifier into a work context object, wherein the work context object is used to define properties that flow across remote requests and enable downstream components of the service access gateway to work in a same context of an invoking client; forwarding the first service invocation to a recipient; receiving a second service invocation to the service access gateway, wherein said second service invocation contains a second service correlation identifier in a second request context; associating the first service invocation with the second service invocation in the service access gateway upon matching the first service correlation identifier with the second service correlation identifier; and performing one or more functions based on the associations between the first and second service invocations using a custom service correlation service that implements an extensible application programming interface.