Update api with registering handlers, middleware and authentication

api/middleware.go

@@ -0,0 +1,27 @@
+package api
+
+import "net/http"
+
+// Middleware is a function that can be added as a middleware to the API endpoint.
+type Middleware func(next http.Handler) http.Handler
+
+type mwHandler struct {
+	handlers []Middleware
+	final    http.Handler
+}
+
+func (mwh *mwHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
+	handlerLock.RLock()
+	defer handlerLock.RUnlock()
+
+	// final handler
+	handler := mwh.final
+
+	// build middleware chain
+	for _, mw := range mwh.handlers {
+		handler = mw(handler)
+	}
+
+	// start
+	handler.ServeHTTP(w, r)
+}