Not sure exactly if this is what you need but probably you can implement your own backend app to communicate with FusionAuth however you see fit. Just like what I did here in NestJS. Then in my react app I have a normal form and then sends an HTTP request to my backend endpoint. So in other word I am not using startLogin
helper function.
Yes, I know it is not angular. But just to light your creativity I thought it is a good idea too look at it from a different perspective.
BTW I appreciate it if you could give my repo a star if it did help you.