POST form data without = in payload

Is it possible to do an HTTP POST using a form and not receive = in the payload?

I want to just send the string directly, because the API does not support data as a query string parameter, but expect the body to contain the data I am sending.

So instead of something like:

<form action="POST" action="http://somewhere/">
  <input type="hidden" name="key" value="value" />
</form>

      

        
        
        
      

    

which will create an HTTP POST payload body: ' key=value

'

I want to HTTP POST create a form with payload: ' value

'

It's easy to do this with CORS and XHR, but I really have no control over this service and would like to do a POST without setting a proxy in the middle with CORS. Is it even possible with use <form>

?