Traefik dashboard needs to be enabled (doc) and you need to use the same name: you create test-auth middleware and assign non-existing auth middleware.
Maybe check simple Traefik example.
Error 526 is an SSL certificate error that occurs when Cloudflare cannot verify the SSL certificate presented by the origin server.
Maybe that fixes it. If not, share your full Traefik static and dynamic config, and docker-compose.yml if used.