authentik/website/docs/providers/proxy/_traefik_ingress.md

Create a middleware:

apiVersion: traefik.containo.us/v1alpha1
kind: Middleware
metadata:
  name: authentik
spec:
  forwardAuth:
    address: http://outpost.company:9000/akprox/auth/traefik
    trustForwardHeader: true
    authResponseHeaders:
      - X-authentik-username
      - X-authentik-groups
      - X-authentik-email
      - X-authentik-name
      - X-authentik-uid
      - X-authentik-jwt
      - X-authentik-meta-jwks
      - X-authentik-meta-outpost
      - X-authentik-meta-provider
      - X-authentik-meta-app
      - X-authentik-meta-version

Add the following settings to your IngressRoute

By default traefik does not allow cross-namespace references for middlewares:

See here to enable it.

spec:
  routes:
    - kind: Rule
      match: "Host(`app.company`)"
      middlewares:
        - name: authentik
          namespace: authentik
      priority: 10
      services: # Unchanged
    # This part is only required for single-app setups
    - kind: Rule
      match: "Host(`app.company`) && PathPrefix(`/akprox/`)"
      priority: 15
      services:
        - kind: Service
          # Or, to use an external Outpost, create an ExternalName service and reference that here.
          # See https://kubernetes.io/docs/concepts/services-networking/service/#externalname
          name: ak-outpost-example-outpost
          port: 9000