`application/json` is not a supported enctype in HTML. See [MDN documentation](https://developer.mozilla.org/en-US/docs/Web/API/HTMLFormElement/enctype). There was a [proposal](https://www.w3.org/TR/html-json-forms/) for it - note the giant yellow-dotted banner there. It is not actively maintained and as far as I know, no browser supports it. So your problem is more on the client-side than on the server-side. But even if browsers would support it, this would need to be implemented in Jester, because when the parameters reach your own code, the request has already been parsed.
To sum up: Not possible because neither supported on the client nor on the server side. Review your requirements.
