$ cat awful-json.scm
(import awful intarweb spiffy chicken.io)

(define-page (main-page-path)
  (lambda ()
    (let* ((req (current-request))
           (headers (request-headers req))
           (content-length (header-value 'content-length headers)))
      (print (read-string content-length (request-port (current-request))))
      '()))
  no-template: #t
  method: 'post)

$ awful awful-json.scm &
[1] 1652

$ curl --header "Content-Type: application/json" --request POST --data '{"foo":"xyz"}' http://localhost:8080/
{"foo":"xyz"}