Extract backend auth middleware

Dockerfile

@@ -27,6 +27,7 @@ RUN npm ci --omit=dev
 COPY backend/index.js ./index.js
 COPY backend/db.js ./db.js
 COPY backend/config ./config
+COPY backend/middleware ./middleware
 COPY backend/policies ./policies
 COPY backend/services ./services
 COPY backend/utils ./utils