feat(integrations): automatically disable googlereader/fever when not used #3543

When there is no user of Fever/GoogleReader, there is no need to expose their
endpoints. This reduces quite a bit the exposition surface of miniflux, while
not breaking any existing deployments, and is pretty self-contained.

internal/fever/middleware.go

@@ -9,6 +9,7 @@ import (
 	"net/http"
 
 	"miniflux.app/v2/internal/http/request"
+	"miniflux.app/v2/internal/http/response"
 	"miniflux.app/v2/internal/http/response/json"
 	"miniflux.app/v2/internal/storage"
 )
@@ -21,6 +22,29 @@ func newMiddleware(s *storage.Storage) *middleware {
 	return &middleware{s}
 }
 
+func (m *middleware) maybeUnauthorizedFever(next http.Handler) http.Handler {
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		feverUsed, err := m.store.IsFeverUsed()
+		if err != nil {
+			builder := response.New(w, r)
+			builder.WithStatus(http.StatusInternalServerError)
+			builder.WithHeader("Content-Type", "text/plain")
+			builder.Write()
+			return
+		}
+
+		if !feverUsed {
+			builder := response.New(w, r)
+			builder.WithStatus(http.StatusUnauthorized)
+			builder.WithHeader("Content-Type", "text/plain")
+			builder.Write()
+			return
+		}
+
+		next.ServeHTTP(w, r)
+	})
+}
+
 func (m *middleware) serve(next http.Handler) http.Handler {
 	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		clientIP := request.ClientIP(r)