A system is configured to authorize client access to an application programming interface (API) of a host device. A proxy is configured to handle network traffic between a host and a client. Clients engage the host through the proxy to access an API of the host. An authorized client-side application permitted use of the API is distributed to clients and includes a Software Development Kit configured to generate a unique token and provide the token in association with an API request when challenged by the proxy. For example, the proxy may challenge a client to present a token in response to receiving an API request lacking a token or when a token is expired. The proxy verifies the token to authenticate the client and permits authorized clients access to the API by passing API requests received from authenticated clients on to the host for servicing.