Methods to integrate your use case
Regardless of your SaaS application tech stack, the typical integration flow can use three methods:
In this approach the user dashboard html pages are also hosted on SaaSBox. API requests load user specific data from a separate API server. Once integrated and your workflow is settled, you have less work to do with this approach. This is ideal to launch a small SaaS application that requires a handful of custom API calls. In this approach the maintenance burden is limited to your your dashboard UI and those few API calls you need, which is a much smaller surface area compared to managing it all.

SaaSBox hosts the user dashboard UI. Data is loaded from API server on each request
A sub-type of this approach is not using API calls, but simply embedding an application as an iframe inside SaaSBox. You can succesfully launch a service in this way using nocode application building tools such as Bubble, Retool, Appsmith, or Superblocks. Check out our guides on each for details.

In this approach SaaSBox is still your storefront and hosts yourdomain.com. Your application is served at the yourdomain.com/app path through SaaSBox, even when hosted at a separate server. The user session is created and shared with your standalone application.
Both approaches create a clear-cut separation between the generic part of your SaaS maintained by SaaSBox, and the core part of your SaaS maintained by you. Thanks to this separation SaaSBox team can maintain, host and keep the generic part always up to date (saving you ~1-2 developers each month) while you focus your resources on the core part that makes you unique.
As an example, let us assume Stripe changes their API or adds new capabilities. You would not need to worry about such changes, as they will be incorporated and updates pushed to your SaaS by SaaSBox. Similarly user authentication updates can be incorporated with no changes needed by your team.