Today, what are commonly called APIs, or Application Programming Interfaces, group together a raft of inter-application communication methods ranging from web services (REST or SOAP) to local or remote calls between processes (RPCs). These types of web services, while not the only ones to use APIs, have spread like wildfire in recent years, and are now a widely used and essential communication mechanism for all companies that have embraced digital transformation. These days, they can be found in an increasing number of use cases: public, personal, and sensitive data – mobile applications, exchanges between partners, the IoT, so-called ”client-side“ applications, and so on.