Application Programming Interfaces (APIs) are a standard feature of any application that exposes its functionalities to external invokers. APIs can becomposed thus obtaining new programs with new functionalities. However API composition easily becomes a frustrating and time-costly task that hinders API reuse. The issue derives from technology-dependent features of API composition such as the need of extensive documentation, protocol integration, security issues, etc.. In this paper we introduce the perspective of the API-as-a-Service (APIaaS) layer as tool to ease the development and deployment of applications based on API composition, abstracting communication protocols and message formats. We elicit the desirable features of such a layer and provide a proof-of-concept prototype implemented using a service-oriented language.