This curl command uploads the firmware upgrade file to the device and checks it. (This option includes checking the upgrade file signature.)

curl -i -k -b /tmp/headers --http1.0 -F file=@rcell_mtr_upgrade.bin "https://192.168.2.1/api/command/firmware_check?check_signature=0&token=5CD884F57998F12731C95C95C4D4087"

HTTP/1.0 200 OK
Access-Control-Allow-Origin: *|
Set-Cookie: token=5CD884F57998F12731C95C95C4D4087; Path=/; Secure
Cache-Control: no-cache
Content-type: text/plain
Content-Length: 67
Connection: close
Date: Wed, 13 Jun 2018 19:46:26 GM
Server: rcell

{
   "code" : 200,
   "status" : "success",
   "type" : "upload"
}