A B767-300 Captain refused to accept Dispatch's unilateral deferral of the APU for his ETOPS flight; citing the requirement for the Captain's concurrence to do so.

Narrative

Half an hour before schedule departure I called for the windshields to be washed. Fifteen minutes later the APU auto-shutdown. Five minutes after a mechanic shows up; even though he was said to be 'unavailable' to clean the windshields 20 minutes earlier (I suspect due to under staffing. Apparently a windshield wash was NOT as important as addressing a dispatch item that prevents an 'on-time' departure).The Mechanic restarted the APU and it appeared to be operating normally. He then left the cockpit to 'bite-check' the APU computer to determine the cause of the auto-shutdown. Near departure time I received an ACARS message from Dispatch stating 'APU DEFERRED INOP!' This was done unilaterally by a station Maintenance Supervisor WITH NO CONCURRENCE; INPUT OR DISCUSSION WITH THE CAPTAIN; directly opposed to established protocol for international flights! I called Dispatch to clarify 'what the heck was going on' inasmuch as the APU had been operating normally yet was now DEFERRED INOP! This deferral REQUIRES CAPTAIN'S CONCURRENCE. I believe the station Maintenance Supervisor tried to DIRECTLY CIRCUMVENT THE CAPTAIN'S AUTHORITY and ERODE THAT AUTHORITY IN THE NAME OF SCHEDULE EFFICIENCY OR OTHER 'COST-SAVING' POLICY ESTABLISHED BY MANAGEMENT. Without our back-up generator (one THIRD OF OUR CAPACITY) or alternative pressurization source supplied by the APU in an ETOPS arena; I had every right to know why the APU shutdown and if there was a possibility of fixing it with minor maintenance efforts. They tried to circumnavigate my authority as PIC. After determining the cause of the shutdown (ONLY AT MY INSISTENCE); and after discussion with other flight officers; we; collectively; determined it was safe to accept the deferral and departed about: 40 minutes late. It seemed that station management was more interested in getting the plane gone; than addressing safety and authoritative; collective protocol.