`curl`'ing a Tailscale Webhook

November 14, 2022 - One minute read - 138 words

[Tailscale] is really good. I’ve been using it as a virtual private network to span 2 home networks and to securely (!) access my hosts when I’m remote.

Recently Tailscale added Webhook functionality to permit processing subscribed-to (Tailscale) events. I’m always a sucker for a webhook ;-)

Here’s a curl command to send a test event to a Tailscale Webhook:

URL=""

# From Tailscale's docs
# https://tailscale.com/kb/1213/webhooks/#events-payload
BODY='
[
  {
    "timestamp": "2022-09-21T13:37:51.658918-04:00",
    "version": 1,
    "type": "test",
    "tailnet": "example.com",
    "message": "This is a test event",
    "data": null
  }
]
'

T=$(date +%s)
V=$(\
  printf "${T}.${BODY}" \
  | openssl dgst -sha256 -hmac "${SECRET}" -hex -r \
  | head --bytes=64)

curl \
--request POST \
--header "Tailscale-Webhook-Signature:t=${T},v1=${V}" \
--header "Content-Type: application/json" \
--data "${BODY}" \
https://${URL}

There must be a better way of extracting the hashed value from the openssl output.