The first visible result of the REXEC and AUTH commands is a process called 'dmlibsrv' on the remote machine. 'dmlibsrv' runs with the operating system security credentials of the build area. If you are a UNIX superuser, you can see this process and check which user it is using, by using the 'ps -elf' command at the UNIX prompt. From SDSF on MVS you can see this process from the 'PS' display.
The process 'dmlibsrv' now runs the build. All actions are performed from this user.