The HTTP API has a Stop command, though you need the session ID, which would be present in the DB or when you start it. (you should probably save the session idds in the workqueue - GetSessionId() )
Build a Blue Prism Process (lets call it StopAllSessions) to work through all Pending Items in the “SessionID” Queue and use a command line (use the Utility – Environment VBO) to send a /requeststop to each Session ID (see help pages) - Expose this as a webservice.
The HTTP API also has a Shutdown command to close down the resource PC.
