Matching on base domain as the default was surprising to me when I started using Bitwarden... treating subdomains as the same seems dangerous.
Actually it's mostly financial institutions that I've seen this happen with. Have to wonder if they all share the same web auth library that runs on the Z mainframe, or there's some arcane page of the SOC2 guide that mandates a minimum of 3 redirects to confuse the man in the middle.