Ah sorry for both, the README sample is here from the start (4 years) ago that I didn't take time to read it with a fresh eye:

  POST https://acmecorp.net/login?user=toto&password=1234

In the README is doing a POST request with user and paasword parameter in the URL.

  POST https://acmecorp.net/login
  [Form]
  user: toto
  password: 1234

Is a more traditional POST with user and password in the body. Probably going to update the READMEs sample Issue created here [1]!

[1]: https://github.com/Orange-OpenSource/hurl/issues/4151