Webtask's source IP / CIDR?

What is the source IP or IP-range (CIDR) for a webtask calling out, e.g. to Splunk? Specifically in the https://sandbox-eu.it.auth0.com
I want to restrict the Splunk access to these IPs.

If I remember correctly, the source webtask IPs are the same as those listed in the Rules and Custom DB editors (these things are just code running on webtasks):