Pretty much as the title says - doesn't look like it's supported:

https://github.com/http4k/http4k/blob/59c9814cae8203857e30138501e979366f797817/http4k-testing-webdriver/src/main/kotlin/org/http4k/webdriver/JSoupWebElement.kt#L83

I'm taking a look and seeing if I can put together a PR

Last changes allow to create form login on authorization endpoint.
It might be unclear how to do it. This could be added to documentation.

Suggested test cases:

• It should throw proper exception when article does not exist.
• If the user has not been favorited the article before, the handler should not throw exceptions.
• It should throw exception when the article author not found.
• It should return proper values for the return object.