I've been fighting this issue for the past 2 days, and I finally have the solution. Not an explanation, a solution.
The important like in @DirkieP's configuration is:
- "traefik.http.middlewares.oo-header.headers.customRequestHeaders.X-Forwarded-Proto=https"
(and it's accompanying middleware attachment)
For the life of me, I can't work out why this is needed,, as according to https://github.com/containous/whoami/, my traefik is already sending X-Forwarded-Proto: https, but hey, it's working.
I hope this prevents someone else from banging their head against their desk for 2 days!