Wrong redirect when using self-hosted Kratos

Hello!

I'm not sure if I am doing something wrong, but it seems there is an assumption here that may not be correct in cases of self-hosted Kratos:
https://github.com/ory/elements/blob/fdabadf8cb2e0ec4fd9286a5277516f8fd69aa0c/packages/nextjs/src/utils/rewrite.ts#L32C1-L32C62

In my Kratos config, I have:

kratos:
  kratos:
    config:
      serve:
        public:
          base_url: https://auth.example.com
          cors:
            allowed_origins:
              - http://localhost:3042
              - https://auth.example.com

      selfservice:
        default_browser_return_url: https://example.com
        allowed_return_urls:
          - http://localhost:3042/*
          - https://example.com/*

        methods:
          webauthn:
            config:
              rp:
                id: example.com
                origin: https://example.com:443/auth/login

        flows:
          error:
            ui_url: https://example.com/error
          
          settings:
            ui_url: https://example.com/settings

          recovery:
            ui_url: https://example.com/auth/recovery
          
          verification:
            ui_url: https://example.com/auth/verification
            after:
              default_browser_return_url: https://example.com
          
          logout:
            after:
              default_browser_return_url: https://example.com
          
          login:
            ui_url: https://example.com/auth/login

          registration:
            ui_url: https://example.com/auth/registration

Every time I start a flow, I get redirected to the UI URLs specified in the config, as-is.
In the linked code above, we can see it tries to match the base URL (let's say https://auth.example.com with the redirect https://example.com/auth/login). Of course, this do not match, it gives up and returns the URL as-is from the backend. It seems a bit weird to me that Ory HAS to be hosted on the same domain as the actual app handling the flows. I suppose this is something specific to the hosted version of Kratos/Ory services, and I also suppose the headers passed are supposed to mitigate this issue, but they do not have any effects in the self-hosted version, it seems.

I'm absolutely open to making a PR if required; I just want to make sure there was no oversight on my side first!

Thanks a lot.

Start in packages/nextjs/src/utils/rewrite.ts at the linked matching logic, then reproduce a flow using the self-hosted Kratos configuration and differing auth and application domains. Determine the expected redirect behavior for configured UI URLs, add or update focused coverage if the repository provides it, and verify that flow redirects no longer incorrectly fall back to the backend URL.