The “origin as” as observed via ARIN RDAP is a difficult-to-use relic from the past. The concept of “Autonomous System Originations” pre-dates IRR and RPKI. It was the best possible solution at that time; but since then superior solutions became available.
I submitted a policy proposal to deprecate this functionality in full:
Perhaps a different approach applicable to your objectives is to merge RDAP information with RPKI derived information (both in JSON format). Through this path one can achieve both a more fine-grained granularity (RPKI ROAs can be configured at routing boundaries, rather than assignment boundaries), and have greater assurances the information was produced by the Internet Number Resource holder.
A frequently updated JSON formatted view on the RPKI can be found here:
https://console.rpki-client.org/vrps.json (this kind of file can also be produced by installing an RPKI validator on your own infrastructure).
Kind regards,
Job