Add example using github oauth application

examples/external-auth/nginx/dashboard-ingress.yaml

@@ -0,0 +1,38 @@
+apiVersion: extensions/v1beta1
+kind: Ingress
+metadata:
+  annotations:
+    ingress.kubernetes.io/auth-signin: https://$host/oauth2/sign_in
+    ingress.kubernetes.io/auth-url: https://$host/oauth2/auth
+  name: external-auth-oauth2
+  namespace: kube-system
+spec:
+  rules:
+  - host: __INGRESS_HOST__
+    http:
+      paths:
+      - backend:
+          serviceName: kubernetes-dashboard
+          servicePort: 80
+        path: /
+
+---
+
+apiVersion: extensions/v1beta1
+kind: Ingress
+metadata:
+  name: oauth2-proxy
+  namespace: kube-system
+spec:
+  rules:
+  - host: __INGRESS_HOST__
+    http:
+      paths:
+      - backend:
+          serviceName: oauth2-proxy
+          servicePort: 4180
+        path: /oauth2
+  tls:
+  - hosts:
+    - __INGRESS_HOST__
+    secretName: __INGRESS_SECRET__