Not sure what more I can add here, so if you could come forth with questions that would be best.
Aggregate all (or more complex) operations your custom front-end would do, write a single function for each one of them, and then use them in your webapp.
Let me break it down a bit…
Integration gateway’s initial requirement/implementation was to handle webhooks and asynchronous requests, so there (currently) isn’t much flexibility in formatting responses (for GET /ap/some/data
as an example). Extensions are planned to be added but I don’t have a timeline for that. Authentication is not covered by the built-in auth system.
Sink routes are more flexible and allow you to set nearly anything as far as the HTTP response goes (headers, content, …).
The problem you’d have with sink routes is that you need to provide a sink signature in order for the request to be considered as authorized.
If you’ll only be building a web application (just the front-end) this won’t be ok for you. If you’ll be building a front-end with an intermediate API (like I’ve mentioned in my first reply), then you can use them (just make sure the signatures are hidden on the back-end).
Explicit automation can be invoked via REST API, they are protected by the built-in authentication (those JWT tokens and such).
They also allow you to set some response data so they could be used as custom API endpoints but you’d need to experiment with them a bit.
The last time I used them like so was in 2021.9
(I think) with server automation scripts.
Conclusion
I would suggest you start off with the SDK suggestion. We can discuss custom endpoints when/if we get to that point.