Unlike RPKI ROA validation, which protects against origin AS manipulation, Autonomous System Provider Authorization (ASPA) provides path plausibility, increasing the likelihood of catching the valley-free routing violation type of route leaks. https://manrs.org/2023/02/unpacking-the-first-route-leak-prevented-by-aspa/ provides a summary of ASPA. In essence, an AS participating in ASPA must publish an ASPA record, defining the Set of Provider ASes, which is a list of valid Transit ASes for AS14907. This is the draft ASPA profile, and this explains the verification algorithm.
Unfortunately, broad support for ASPA validation is estimated no sooner than 2026/2027. Nevertheless, it should be possible to publish ASPA records in RPKI through the ARIN portal. I hope the more ASes publish such records, the sooner network vendors (and developers of BGP daemons, e.g. FRR and Bird) will implement ASPA validation.
In June 2024, 77 ASes had published ASPA records. At first glance, Wikimedia may become the Internet's largest resource to publish ASPA records :)
However, the ASPA record is yet another duplicate of the transit_provider list in Homer, and the export policies defined in our aut-num objects. Our export policies in the IRRs already do not match up what's in Homer (for instance, we removed a few Transit providers during the knams migration, but they're still present in our export policies), and adding an ASPA record will make it even harder to stay in sync. Perhaps we can script something that checks whether the IRRs and ASPA record(s) still match with the source of truth, being Homer?