X-Forwarded-Proto not set on request to backend service

Traefik Traefik v2 (latest)
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1

I cannot get Traefik 2.6.1 to send a X-Forwarded-Proto header to my backend service.
I tried everything, including the Headers middleware, setting custom headers etc.

Here is my CLI configuration:

      --entrypoints.metrics.address=:9100/tcp
      --entrypoints.traefik.address=:9000/tcp
      --entrypoints.web.address=:8000/tcp
      --entrypoints.websecure.address=:8443/tcp
      --api.dashboard=true
      --ping=true
      --metrics.prometheus=true
      --metrics.prometheus.entrypoint=metrics
      --providers.kubernetescrd
      --providers.kubernetescrd.allowCrossNamespace=true
      --providers.kubernetesingress
      --entrypoints.web.http.redirections.entryPoint.to=:443
      --entrypoints.web.http.redirections.entryPoint.scheme=https
      --log.level=DEBUG
      --entrypoints.websecure.http.middlewares=default-x-forwarded-proto@kubernetescrd

Here is the headers middleware:

apiVersion: traefik.containo.us/v1alpha1
kind: Middleware
metadata:
  creationTimestamp: "2022-03-29T19:20:52Z"
  generation: 2
  labels:
    k8s-app: traefik
  name: x-forwarded-proto
  namespace: default
  resourceVersion: "11751113"
  uid: e169700f-22e3-4ed6-b3be-077fce408cc9
spec:
  headers:
    customRequestHeaders:
      Foo: Bar
      X-Forwarded-Proto: https
    sslProxyHeaders:
      X-Forwarded-Proto: https
    sslRedirect: true

I have a httpbin service running behind it, and Traefik does not set the request header:

{
  "args": {},
  "headers": {
    "Accept": "*/*",
    "Accept-Encoding": "gzip",
    "Host": "httpbin.redacted.de",
    "User-Agent": "curl/7.72.0",
    "X-Forwarded-Host": "httpbin.redacted.de",
    "X-Forwarded-Server": "traefik-988d545fd-x8wjf"
  },
  "origin": "10.132.0.18",
  "url": "https://httpbin.redacted.de/get"
}