Integration testing the redirect flow (golang)

I’ve followed Sign users in to your web app using the redirect model | Okta Developer and have a working system tested manually against a dev okta domain.

I’d like to write automated integration tests for the whole flow, but am stuck at the redirect step.

I can query my /login route, and I get back html from okta.com containing the username&password form the user is supposed to fill out, but don’t know what query containing what information to what endpoint I’m supposed to make to continue the flow in an automated test, as if I was a user filling out the form in a web brower.

Does anyone have an example of them testing this flow they can share? Or know what the okta.com form does and how to replicate it without a web browser?