An IoT engineer is responsible for security at an organization. Humans and machines need to be allowed to access service

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An IoT engineer is responsible for security at an organization. Humans and machines need to be allowed to access services like database or compute on AWS.
The engineer decides to implement dynamic secrets.
Which method helps to get this implementation accurate from a security point of view?

A. Create a central secret system for humans and machine to obtain very short-lived dynamic secrets to access any service.
B. Humans cannot be trusted, and each time they authenticate they should be issued with dynamic secrets. Machines can be trusted, and they can be issued with static credentials.
C. Maintain a different service associated to secret systems to issue access.
D. After a user is authenticated by any trusted system, the user can be trusted to use any service.