feat(traefik-forward-auth): serve several domains and portals from one instance

A session cookie scoped to one registrable domain is never sent to a host under
another, so an app on a second domain could not be protected by this instance at
all. It failed with a 500 naming the cause: "return URL host does not match any
configured cookie domain".

`domains` is now a list of {domain, authHost}, matching the upstream
`server.domains` schema. The chart previously emitted `server.hostname` and
`cookies.domain`, which are not in 4.14.1's documented options — a deprecated
form that still worked. The single-domain values remain as shorthand and fold
into one entry, so an existing release renders the same protection it did before.

`portals` is a list too. A portal is one OAuth2 client, chosen by the middleware
address, so two portals means two Pocket ID applications — which is how access
can be separated per domain rather than merely shared across them. Each portal
gets its own Middleware and its own mounted secret, under
/var/run/secrets/traefik-forward-auth/<portal>/.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

traefik-forward-auth/templates/_helpers.tpl

@@ -11,3 +11,59 @@ app.kubernetes.io/name: {{ .Chart.Name }}
 app.kubernetes.io/instance: {{ .Release.Name }}
 app.kubernetes.io/version: {{ .Chart.AppVersion | quote }}
 {{- end -}}
+
+{{/*
+  The portals, normalised to one shape.
+
+  A portal is a set of identity providers with its own OAuth2 client, and the
+  middleware address is what selects it — so two portals means two clients, and
+  therefore two Pocket ID applications that can be granted to different people.
+
+  `portals` is the general form. The older single-portal values (`portal.name`,
+  `pocketID`, `existingSecret`, `middleware.name`) still work and are folded into
+  the same shape here, so an existing release keeps rendering exactly as before.
+*/}}
+{{- define "tfa.portals" -}}
+{{- if .Values.portals -}}
+{{- range .Values.portals }}
+- name: {{ .name | quote }}
+  endpoint: {{ .pocketID.endpoint | quote }}
+  clientID: {{ .pocketID.clientID | quote }}
+  existingSecret: {{ required "each portal needs an existingSecret" .existingSecret | quote }}
+  secretKey: {{ .secretKey | default "client-secret" | quote }}
+  middlewareName: {{ .middlewareName | default (printf "%s-%s" $.Release.Name .name) | quote }}
+{{- end }}
+{{- else -}}
+- name: {{ .Values.portal.name | quote }}
+  endpoint: {{ .Values.pocketID.endpoint | quote }}
+  clientID: {{ .Values.pocketID.clientID | quote }}
+  existingSecret: {{ required "existingSecret is required" .Values.existingSecret | quote }}
+  secretKey: "client-secret"
+  middlewareName: {{ include "tfa.middlewareName" . | quote }}
+{{- end -}}
+{{- end -}}
+
+{{/*
+  The domains served, normalised.
+
+  `domain` is the cookie's scope and `authHost` is where this service is reachable
+  for it. A browser will not send a cookie scoped to one registrable domain to a
+  host under another, so an app on a second domain needs its own entry here — not
+  merely a second client.
+*/}}
+{{- define "tfa.domains" -}}
+{{- if .Values.domains -}}
+{{- range .Values.domains }}
+- domain: {{ .domain | quote }}
+  authHost: {{ .authHost | default .domain | quote }}
+{{- end }}
+{{- else -}}
+- domain: {{ required "cookieDomain is required when `domains` is not set" .Values.cookieDomain | quote }}
+  authHost: {{ required "hostname is required when `domains` is not set" .Values.hostname | quote }}
+{{- end -}}
+{{- end -}}
+
+{{/* Where a portal's client secret is mounted. */}}
+{{- define "tfa.secretDir" -}}
+/var/run/secrets/traefik-forward-auth
+{{- end -}}

traefik-forward-auth/templates/configmap.yaml

@@ -1,3 +1,5 @@
+{{- $portals := include "tfa.portals" . | fromYamlArray -}}
+{{- $domains := include "tfa.domains" . | fromYamlArray -}}
 apiVersion: v1
 kind: ConfigMap
 metadata:
@@ -7,21 +9,26 @@ metadata:
 data:
   config.yaml: |
     server:
-      hostname: {{ .Values.hostname | quote }}
+      # One entry per domain served. `domain` scopes the session cookie and
+      # `authHost` is where this service is reachable for that domain.
+      domains:
+        {{- range $domains }}
+        - domain: {{ .domain | quote }}
+          authHost: {{ .authHost | quote }}
+        {{- end }}
 
     tokens:
       sessionLifetime: {{ .Values.tokens.sessionLifetime }}
 
-    cookies:
-      domain: {{ .Values.cookieDomain | quote }}
-
     portals:
-      - name: {{ .Values.portal.name | quote }}
+      {{- range $portals }}
+      - name: {{ .name | quote }}
         providers:
           - pocketID:
-              endpoint: {{ .Values.pocketID.endpoint | quote }}
-              clientID: {{ .Values.pocketID.clientID | quote }}
-              clientSecretFile: "/var/run/secrets/traefik-forward-auth/client-secret"
+              endpoint: {{ .endpoint | quote }}
+              clientID: {{ .clientID | quote }}
+              clientSecretFile: "{{ include "tfa.secretDir" $ }}/{{ .name }}/client-secret"
+      {{- end }}
     {{- with .Values.extraConfig }}
     {{ . | nindent 4 }}
     {{- end }}

traefik-forward-auth/templates/deployment.yaml

@@ -1,3 +1,4 @@
+{{- $portals := include "tfa.portals" . | fromYamlArray -}}
 apiVersion: apps/v1
 kind: Deployment
 metadata:
@@ -43,18 +44,24 @@ spec:
             - name: config
               mountPath: /etc/traefik-forward-auth
               readOnly: true
-            - name: client-secret
-              mountPath: /var/run/secrets/traefik-forward-auth
+            {{- range $portals }}
+            # One directory per portal: each has its own OAuth2 client, so each
+            # has its own secret.
+            - name: client-secret-{{ .name }}
+              mountPath: "{{ include "tfa.secretDir" $ }}/{{ .name }}"
               readOnly: true
+            {{- end }}
           resources:
             {{- toYaml .Values.resources | nindent 12 }}
       volumes:
         - name: config
           configMap:
             name: {{ .Release.Name }}-config
-        - name: client-secret
+        {{- range $portals }}
+        - name: client-secret-{{ .name }}
           secret:
-            secretName: {{ required "existingSecret is required" .Values.existingSecret }}
+            secretName: {{ .existingSecret }}
             items:
-              - key: client-secret
+              - key: {{ .secretKey }}
                 path: client-secret
+        {{- end }}

traefik-forward-auth/templates/middleware.yaml

@@ -1,16 +1,24 @@
 {{- if .Values.middleware.enabled }}
+{{- $portals := include "tfa.portals" . | fromYamlArray -}}
+{{- range $portals }}
+---
 apiVersion: traefik.io/v1alpha1
 kind: Middleware
 metadata:
-  name: {{ include "tfa.middlewareName" . }}
+  # Referenced by apps as <namespace>-<name>@kubernetescrd. Renaming one detaches
+  # protection from every ingress that names it.
+  name: {{ .middlewareName }}
   labels:
-    {{- include "tfa.labels" . | nindent 4 }}
+    {{- include "tfa.labels" $ | nindent 4 }}
 spec:
   forwardAuth:
-    address: "http://{{ .Release.Name }}.{{ .Release.Namespace }}.svc.cluster.local/portals/{{ .Values.portal.name }}"
-    trustForwardHeader: {{ .Values.middleware.trustForwardHeader }}
-    {{- with .Values.middleware.authResponseHeaders }}
+    # The path selects the portal, and therefore which OAuth2 client — which is
+    # how access is separated between domains.
+    address: "http://{{ $.Release.Name }}.{{ $.Release.Namespace }}.svc.cluster.local/portals/{{ .name }}"
+    trustForwardHeader: {{ $.Values.middleware.trustForwardHeader }}
+    {{- with $.Values.middleware.authResponseHeaders }}
     authResponseHeaders:
       {{- toYaml . | nindent 6 }}
     {{- end }}
 {{- end }}
+{{- end }}