API's (and REST API's) need to be carefully protected through mechanisms limiting access on the basis of identity and authorizing and authenticating through managed and controlled mechanisms. Usually certificates and IP-addresses are being used to restrict access to API's, but a more granular approach is advisable from a Security Architecture perspective. Other architectures being used as Integratio Protocols in Digital Manufacturing Platforms are JSON (for its near real time capabilities) and MQ (message bus architectures). The letter being less secure, since it provides a continuous stream of information which is being sent to a destination. 

Authorisation is the process of allowing an entity (humans, systems or devices) to access information systems or facilities where information and processing capabilities are being stored. More practical in an industrial setting for Digital Manufacturing Platforms, an authorized person can get access to an operational machine in order to update it, or investigate its contents. Unauthorized access could be someone who has been able to access the network from the outside, performing actions that have not been authorized and cannot be justified.

Authentication is a means to assess the authorization rules of an entity by means of a set of instruments. In the case of Digital Manufacturing Platforms it would be the instruments like user name and password, and in addition a second factor such as a physical token or a mobile phone that can authenticate the person accessing the platform. The physical token connects the person to something he has, the password to something he knows. 

A third A in the AAA-architecture is related to Access. Once authorized, and authenticated, access can be granted to the location, system, application, and / or information. Access control levels can thus be set up on different layers. These can be physical (access to the country, to the plant, to the building, the room and the environment where the system is located), and logical (using authentication technologies). In Digital Manufacturing Platforms this means the systems could be accessible only on premise, in the factory or for instance in the (private or public) cloud. As a result different access mechanisms needs to be considered, depending on the risk and intended security levels and controls. 

https://en.wikipedia.org/wiki/AAA_(computer_security) ; https://en.wikipedia.org/wiki/Authorization