Detailed view on Azure Function Custom Handlers
Custom Handler is a feature in Azure Functions which lets you bring your own command, script, or executable, and hook it up to Azure Functions Triggers and Bindings. Custom Handler implements a lightweight Web Server. In other words, you can write your own APIs, in any language i.e. it need not be a language supported by Azure functions. You can just hook up your Azure function host with your custom API and let your function act as a proxy.