There is an option to create tsigkey for: zone or pool.
https://docs.openstack.org/api-ref/dns/?expanded=#create-tsigkeys
There is a SCOPE for tsigkey which can be either ZONE or POOL

In fact it’s possible to use Zone ID with SCOPE:POOL to create to create tsigkey or Pools ID with SCOPE:ZONE.

There is no validation on SCOPE value as we would expect it to be.