I actually just finished implementing a very simple JWT single sign-on feature. We don't use the referer for the authentication/authorization. However, having the path/query in the referer does allow our partners to know what (if any) post-login redirect path/query to include in the JWT to provide end users a seamless re-authentication experience.

We could, of course, build the same functionality into our implementation without relying having the path/query in the referer.