Outside of authentication, are you seeking to somehow embed Flarum into your pre-existing app, or have users use it as a separate website/progressive web app? If to completely integrate, that's possible, but would require a custom extension / custom code that would call the Flarum REST API. If you just want authentication (people log into Flarum through your current site), that should be easily doable with just a few extensions.
ravi99 Thanks much... Is there an article which would give me an idea of how to start with the integration.
Each integration is different, but I would recommend that you start by searching around for existing extensions and support questions that try to do something similar.
