How do I make NextAuth work with multiple domains?

I’m building loginos, a sign-in service for products that run on more than one domain. This question comes up a lot, so here is the full answer: the general approach first, then how loginos handles it. Short answer: Leave AUTH_URL and NEXTAUTH_URL unset and turn on trustHost, so Auth.js builds its URLs from the host of each request instead of one... Weiterlesen: How do I make NextAuth work with multiple domains?