fix(lib): close open redirect when in subrequest mode (#1222)

* test(nginx-external-auth): bring up to code standards

Signed-off-by: Xe Iaso <me@xeiaso.net>

* fix(lib): close open redirect when in subrequest mode

Closes GHSA-cf57-c578-7jvv

Previously Anubis had an open redirect in subrequest auth mode due to an
insufficent fix in GHSA-jhjj-2g64-px7c. This patch adds additional
validation at several steps of the flow to prevent open redirects in
subrequest auth mode as well as implements automated testing to prevent
this from occuring in the future.

* docs: update CHANGELOG

Signed-off-by: Xe Iaso <me@xeiaso.net>

---------

Signed-off-by: Xe Iaso <me@xeiaso.net>

test/nginx-external-auth/deployment.yaml

@@ -12,39 +12,37 @@ spec:
         app: nginx-external-auth
     spec:
       volumes:
-      - name: config
-        configMap:
-          name: nginx-cfg
-      containers:
-      - name: www
-        image: nginx:alpine
-        resources:
-          limits:
-            memory: "128Mi"
-            cpu: "500m"
-          requests:
-            memory: "128Mi"
-            cpu: "500m"
-        ports:
-        - containerPort: 80
-        volumeMounts:
         - name: config
-          mountPath: /etc/nginx/conf.d
-          readOnly: true
-      - name: anubis
-        image: ttl.sh/techaro/anubis-external-auth:latest
-        imagePullPolicy: Always
-        resources:
-          limits:
-            cpu: 500m
-            memory: 128Mi
-          requests:
-            cpu: 250m
-            memory: 128Mi
-        env:
-        - name: TARGET
-          value: " "
-        - name: REDIRECT_DOMAINS
-          value: nginx.local.cetacean.club
-
-
+          configMap:
+            name: nginx-cfg
+      containers:
+        - name: www
+          image: nginx:alpine
+          resources:
+            limits:
+              memory: "128Mi"
+              cpu: "500m"
+            requests:
+              memory: "128Mi"
+              cpu: "500m"
+          ports:
+            - containerPort: 80
+          volumeMounts:
+            - name: config
+              mountPath: /etc/nginx/conf.d
+              readOnly: true
+        - name: anubis
+          image: ttl.sh/techaro/anubis:latest
+          imagePullPolicy: Always
+          resources:
+            limits:
+              cpu: 500m
+              memory: 128Mi
+            requests:
+              cpu: 250m
+              memory: 128Mi
+          env:
+            - name: TARGET
+              value: " "
+            - name: REDIRECT_DOMAINS
+              value: nginx.local.cetacean.club