allow preserving the originally requested path after the authentication redirect

[colearendt]

In most (all?) cases, traefik makes the forwardAuth request at the root of the server (/). This means that the user's requested path is lost in the authentication redirect. However, the prefix is sent along with the X-Forwarded-Prefix header, so we use that in addition to the requested path if the requested path is empty.

https://github.com/traefik/traefik/blob/c57876c116ebc375becaff476fbcf6f25c4db7f3/pkg/middlewares/auth/forward.go#L57

https://github.com/traefik/traefik/blob/c57876c116ebc375becaff476fbcf6f25c4db7f3/pkg/middlewares/auth/forward.go#L102

close #323 close #325

[Menschomat]

Will this ever lead to a new release?