So far in this book, all the interactions between services were done without any form of authentication or authorization. Each HTTP request would happily return a result. This can't happen in production for two simple reasons: we need to know who is calling the service (authentication) and we need to make sure that the caller is allowed to perform the call (authorization). For instance, we probably don't want an anonymous caller to delete entries in a database.
In a monolithic web application, authentication happens with a login form, and once the user is identified, a cookie is set and used for all subsequent requests.
In a microservice-based architecture, we can't use that scheme everywhere because services are not users and won't use web forms to authenticate. We need a way to allow or reject a call between each service automatically...
