Amazon and Microsoft both have IoT services that manage message and state brokering. These sort of services generally require machines to have unique security certificates embedded into the firmware so that they can securely authenticate with the service.
How do these sort of security certificates find their way into the firmware of mass manufactured products? Is it the manufacturers job to burn the firmware onto the microcontroller with a unique security certificate installed per machine? Or does a company hire their own workers to accept shipment on microcontrollers, load the firmware, and send them off to the manufacturers pre-loaded?
Curious how this is actually done in practice.