feat(gitea): add Kerberos SPNEGO proxy for git.prole.org SSO

Deploys an Apache + mod_auth_gssapi sidecar in the gitea namespace that
handles SPNEGO/Kerberos negotiation (HTTP/git.prole.org@PROLE.ORG) and
injects X-WEBAUTH-USER for Gitea reverse-proxy auto-login.

Identity chain:
  Browser → Traefik TLS → Kong → gitea-spnego-proxy:4000
    → GSSAPI negotiate → X-WEBAUTH-USER: <username>
    → gitea-http:3000 (reverse proxy auto-registration)

Changes:
- gitea-spnego-proxy.yaml: krb5.conf ConfigMap + Deployment + Service
- gitea/spnego-proxy/: Dockerfile and Apache vhost (build source)
- kong-configmap.yaml: route git.prole.org → gitea-spnego-proxy:4000

Gitea reverse proxy settings applied via helm upgrade:
  ENABLE_REVERSE_PROXY_AUTHENTICATION=true
  ENABLE_REVERSE_PROXY_AUTO_REGISTRATION=true
  REVERSE_PROXY_AUTHENTICATION_USER_HEADER=X-WEBAUTH-USER

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

deploy/opentofu/k3s/manifests/knoe/gitea-spnego-proxy.yaml

@@ -0,0 +1,126 @@
+# gitea-spnego-proxy.yaml
+# Apache + mod_auth_gssapi sidecar that handles SPNEGO/Kerberos negotiation for
+# git.prole.org. Sits between Kong and Gitea; injects X-WEBAUTH-USER for reverse
+# proxy auto-login.  Gitea remains on port 3000 (cluster-internal); this proxy
+# listens on port 4000 and is the Kong upstream target.
+#
+# Identity chain:
+#   Browser → Traefik TLS → Kong → gitea-spnego-proxy:4000
+#     → GSSAPI (HTTP/git.prole.org@PROLE.ORG keytab)
+#     → X-WEBAUTH-USER: <username>
+#     → gitea-http.gitea:3000
+---
+apiVersion: v1
+kind: ConfigMap
+metadata:
+  name: gitea-krb5-conf
+  namespace: gitea
+data:
+  krb5.conf: |
+    [libdefaults]
+        default_realm = PROLE.ORG
+        dns_lookup_realm = false
+        dns_lookup_kdc = false
+        forwardable = true
+        renewable = true
+        rdns = false
+
+    [realms]
+        PROLE.ORG = {
+            kdc = prole-kerberos-ad-dc.knoe-system.svc.cluster.local:88
+            admin_server = prole-kerberos-ad-dc.knoe-system.svc.cluster.local:88
+        }
+        PROLE.LOCAL = {
+            kdc = authority-prole-auth.knoe-system.svc.cluster.local:88
+            admin_server = authority-prole-auth.knoe-system.svc.cluster.local:749
+        }
+
+    [domain_realm]
+        .prole.org = PROLE.ORG
+        prole.org = PROLE.ORG
+        .prole.local = PROLE.LOCAL
+        prole.local = PROLE.LOCAL
+---
+apiVersion: apps/v1
+kind: Deployment
+metadata:
+  name: gitea-spnego-proxy
+  namespace: gitea
+  labels:
+    app: gitea-spnego-proxy
+spec:
+  replicas: 1
+  selector:
+    matchLabels:
+      app: gitea-spnego-proxy
+  template:
+    metadata:
+      labels:
+        app: gitea-spnego-proxy
+    spec:
+      nodeSelector:
+        kubernetes.io/hostname: gandalf.prole.org
+      containers:
+        - name: proxy
+          image: myrddin.prole.org:5000/gitea-spnego-proxy:latest
+          imagePullPolicy: Always
+          ports:
+            - name: http
+              containerPort: 4000
+              protocol: TCP
+          env:
+            - name: KRB5_CONFIG
+              value: /etc/krb5.conf
+            - name: KRB5_KTNAME
+              value: /etc/krb5/http.keytab
+          volumeMounts:
+            - name: keytab
+              mountPath: /etc/krb5
+              readOnly: true
+            - name: krb5-conf
+              mountPath: /etc/krb5.conf
+              subPath: krb5.conf
+              readOnly: true
+          livenessProbe:
+            tcpSocket:
+              port: 4000
+            initialDelaySeconds: 10
+            periodSeconds: 30
+            failureThreshold: 3
+          readinessProbe:
+            tcpSocket:
+              port: 4000
+            initialDelaySeconds: 5
+            periodSeconds: 10
+          resources:
+            requests:
+              cpu: 10m
+              memory: 64Mi
+            limits:
+              cpu: 200m
+              memory: 128Mi
+      volumes:
+        - name: keytab
+          secret:
+            secretName: gitea-krb5-keytab
+            defaultMode: 0400
+        - name: krb5-conf
+          configMap:
+            name: gitea-krb5-conf
+---
+apiVersion: v1
+kind: Service
+metadata:
+  name: gitea-spnego-proxy
+  namespace: gitea
+  labels:
+    app: gitea-spnego-proxy
+spec:
+  selector:
+    app: gitea-spnego-proxy
+  ports:
+    - name: http
+      port: 4000
+      targetPort: 4000
+      protocol: TCP
+  type: ClusterIP

deploy/opentofu/k3s/manifests/knoe/kong-configmap.yaml

@@ -77,8 +77,10 @@ data:
               - /
             strip_path: false
 
+      # Gitea: routed through gitea-spnego-proxy (Apache + mod_auth_gssapi) which
+      # negotiates SPNEGO/Kerberos and injects X-WEBAUTH-USER for reverse proxy login.
       - name: gitea-http
-        url: http://gitea-http.gitea.svc.cluster.local:3000
+        url: http://gitea-spnego-proxy.gitea.svc.cluster.local:4000
         routes:
           - name: gitea-root
             hosts:

gitea/spnego-proxy/Dockerfile

@@ -0,0 +1,17 @@
+FROM debian:bookworm-slim
+
+RUN apt-get update && \
+    apt-get install -y --no-install-recommends \
+        apache2 \
+        libapache2-mod-auth-gssapi \
+        krb5-user \
+        ca-certificates && \
+    rm -rf /var/lib/apt/lists/* && \
+    a2enmod proxy proxy_http headers auth_gssapi rewrite
+
+COPY gitea-spnego.conf /etc/apache2/sites-available/gitea-spnego.conf
+RUN a2dissite 000-default && a2ensite gitea-spnego
+
+EXPOSE 4000
+
+CMD ["apache2ctl", "-D", "FOREGROUND"]

gitea/spnego-proxy/gitea-spnego.conf

@@ -0,0 +1,35 @@
+Listen 4000
+
+<VirtualHost *:4000>
+    ServerName git.prole.org
+
+    LogLevel info
+    ErrorLog /proc/self/fd/2
+    CustomLog /proc/self/fd/1 combined
+
+    # Health check endpoint — no auth required (used by k8s probes)
+    <Location /_healthz>
+        AuthType None
+        Require all granted
+    </Location>
+
+    # GSSAPI/SPNEGO — all other paths require a valid Kerberos ticket
+    # Keytab contains HTTP/git.prole.org@PROLE.ORG (stored as gitea-krb5-keytab secret)
+    <Location />
+        AuthType GSSAPI
+        AuthName "Kerberos - PROLE.ORG"
+        GssapiCredStore keytab:/etc/krb5/http.keytab
+        GssapiLocalName on
+        Require valid-user
+
+        # Inject bare username into X-WEBAUTH-USER for Gitea reverse proxy login.
+        # Strip the @REALM suffix if GssapiLocalName didn't resolve it.
+        RequestHeader set X-WEBAUTH-USER "%{REMOTE_USER}e"
+        RequestHeader edit X-WEBAUTH-USER "@.*$" ""
+    </Location>
+
+    ProxyPreserveHost On
+    ProxyPass /_healthz !
+    ProxyPass / http://gitea-http.gitea.svc.cluster.local:3000/
+    ProxyPassReverse / http://gitea-http.gitea.svc.cluster.local:3000/
+</VirtualHost>