Desenvolvimeto de app mobile para criar interfaces gráficas baseadas em html de forma flexível.

I need an app that can behave like a webserver, to serve static files for himselfe to render UX. Initially, the files will be loaded from a webserver hosted in a local network. Then when the user opens the app from another network, the same files should be available as they where oppened from LAN server.
Almost like a SPA. The only difference is on js calls to mqtt server, that instead of getting data from lan server, the connection is now to a cloud server hosted on internet and data is forwarded to and from the lan server. In short, this app must allow the user to have the same experience acessing webpages when he is directly accessing the LAN server or when he is abroad.
A cloud server (mqtt preferably) can handle live data exchange, where´s no need to reload all webpages. Live data exchange is used to get status and send commands to automation devices controlled by the LAN server.
Perhaps there is a better approuch or solution for this scenario, and suggestions are well apreciated.
Since there are many lan servers, and each one has a different ux and different webpages, there is no single ux that could be used for all servers and we don´t want to devolop a app for each client.