You can use Capacitor for this; if you’ve already built the website for mobile and you’re happy with it, you don’t need to use the Ionic components. The advantage of the Ionic components is that they adopt the design of the platform the app is run on (Apple style on iOS, Google style on Android), but if you don’t want/need this, you can just get your website running “as an app” with Capacitor.
If you have an existing website, it should be pretty straightforward, but since you have login and the app will communicate with the website, I would make my network calls with the HTTP Plugin, as that can avoid CSRF issues.