nginx - log post body to stdout

nginx.conf

      location /events {
         if ($request_method = POST) {
            access_log  /dev/stdout post_body if=$loggable;
            proxy_pass $scheme://127.0.0.1/logsink;
            break;
         }
         return 200 "ok";
      }

      location /logsink {
        return 200 "ok";
      }

        map $request_body $loggable {
          ''      0;
          '-'     0;
          default 1;
        }