Authentication is the process of identifying whether a client is genuine or not. When a server authenticates a client, it checks the username/password pair and creates session cookie/JWT.
Authorization is the process of differentiating one client from another after a successful authentication. In cloud services, the resources requested by a client need to be served by checking that the resources belong to that client but not the other client. The permissions and access to resources vary for different clients. For example, the admin has the highest privileges of resources. A normal user's access is limited.