webhook_url: https://developers.viawallet.com
tonce: 1513746038205

echo -n 'https://developers.viawallet.com?tonce=1513746038205' | openssl dgst -sha256 -hmac "mpEFG56Nc9u5fUFjrg9mWoTEe8uk343X"
# output: b9d55b0c5385137611542f8b85178329e5cbec22cb0780f9d9c3ce07f778ba9f

# added header
X-SIGNATURE: b9d55b0c5385137611542f8b85178329e5cbec22cb0780f9d9c3ce07f778ba9f