chore: add kubernetes example

Author: shaj13

README.md

@@ -35,6 +35,7 @@ Here are a few bullet point reasons you might like to try it out:
 * provides a mechanism to customize strategies, even enables writing a custom strategy
 
 ## Strategies
+* [kubernetes (Token Review)](https://pkg.go.dev/github.com/shaj13/go-guardian/auth/strategies/kubernetes?tab=doc)
 * [Certificate-Based](https://pkg.go.dev/github.com/shaj13/[email protected]/auth/strategies/x509?tab=doc)
 * [Bearer-Token](https://pkg.go.dev/github.com/shaj13/[email protected]/auth/strategies/bearer?tab=doc)
 * [Static-Token](https://pkg.go.dev/github.com/shaj13/[email protected]/auth/strategies/bearer?tab=doc)

_examples/kubernetes/main.go

@@ -0,0 +1,71 @@
+// Copyright 2020 The Go-Guardian. All rights reserved.
+// Use of this source code is governed by a MIT
+// license that can be found in the LICENSE file.
+
+package main
+
+import (
+	"context"
+	"fmt"
+	"log"
+	"net/http"
+	"time"
+
+	"github.com/gorilla/mux"
+
+	"github.com/shaj13/go-guardian/auth"
+	"github.com/shaj13/go-guardian/auth/strategies/kubernetes"
+	"github.com/shaj13/go-guardian/auth/strategies/token"
+	"github.com/shaj13/go-guardian/store"
+)
+
+// Usage:
+// Run kubernetes mock api and get agent token
+// go run mock.go
+// Request server to verify token and get book author
+// curl  -k http://127.0.0.1:8080/v1/book/1449311601 -H "Authorization: Bearer <agent-token-from-mock>"
+
+var authenticator auth.Authenticator
+var cache store.Cache
+
+func main() {
+	setupGoGuardian()
+	router := mux.NewRouter()
+
+	router.HandleFunc("/v1/book/{id}", middleware(http.HandlerFunc(getBookAuthor))).Methods("GET")
+	log.Println("server started and listening on http://127.0.0.1:8080")
+	http.ListenAndServe("127.0.0.1:8080", router)
+}
+
+func getBookAuthor(w http.ResponseWriter, r *http.Request) {
+	vars := mux.Vars(r)
+	id := vars["id"]
+	books := map[string]string{
+		"1449311601": "Ryan Boyd",
+		"148425094X": "Yvonne Wilson",
+		"1484220498": "Prabath Siriwarden",
+	}
+	body := fmt.Sprintf("Author: %s \n", books[id])
+	w.Write([]byte(body))
+}
+
+func setupGoGuardian() {
+	authenticator = auth.New()
+	cache = store.NewFIFO(context.Background(), time.Minute*10)
+	kubeStrategy := kubernetes.New(cache)
+	authenticator.EnableStrategy(token.CachedStrategyKey, kubeStrategy)
+}
+
+func middleware(next http.Handler) http.HandlerFunc {
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		log.Println("Executing Auth Middleware")
+		user, err := authenticator.Authenticate(r)
+		if err != nil {
+			code := http.StatusUnauthorized
+			http.Error(w, http.StatusText(code), code)
+			return
+		}
+		log.Printf("User %s Authenticated\n", user.UserName())
+		next.ServeHTTP(w, r)
+	})
+}

_examples/kubernetes/mock.go

@@ -0,0 +1,72 @@
+// Copyright 2020 The Go-Guardian. All rights reserved.
+// Use of this source code is governed by a MIT
+// license that can be found in the LICENSE file.
+
+package main
+
+import (
+	"fmt"
+	"io/ioutil"
+	"log"
+	"net/http"
+	"strings"
+
+	"github.com/gorilla/mux"
+)
+
+const (
+	agentJWT          = "eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJzdWIiOiIxMjM0NTY3ODkwIiwibmFtZSI6IkpvaG4gRG9lIiwiaWF0IjoxNTE2MjM5MDIyfQ.SflKxwRJSMeKKF2QT4fwpMeJf36POk6yJV_adQssw5c"
+	serviceJWT        = "eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJzdWIiOiIxMjM0NTYiLCJuYW1lIjoic3lzdGVtOnNlcnZpY2U6YWNjb3VudCIsImlhdCI6MTUxNjIzOTAyMn0.4pHu9y6vJvtOnLhpz7M3Znnvcdpm7GCiHPCPYzyxps8"
+	authenticatedUser = `
+	{
+		"metadata":{
+		   "creationTimestamp":null
+		},
+		"spec":{
+	 
+		},
+		"status":{
+		   "authenticated":true,
+		   "user":{
+			  "username":"system:serviceaccount:curl_agent",
+			  "uid":"1"
+		   }
+		}
+	}
+	`
+	unauthenticatedUser = `
+	{
+		"metadata":{
+		   "creationTimestamp":null
+		},
+		"spec":{
+	 
+		},
+		"status":{
+		   "authenticated":false,
+		}
+	}
+	`
+)
+
+func main() {
+	log.Printf("JWT service account For auth startegy: %s \n", serviceJWT)
+	log.Printf("JWT service account For curl agent: %s \n", agentJWT)
+
+	router := mux.NewRouter()
+	router.HandleFunc("/apis/authentication.k8s.io/v1/tokenreviews", http.HandlerFunc(review)).Methods("POST")
+	log.Println("Kube Mock API Server started -> http://127.0.0.1:6443")
+	http.ListenAndServe("127.0.0.1:6443", router)
+}
+
+func review(w http.ResponseWriter, r *http.Request) {
+	body, _ := ioutil.ReadAll(r.Body)
+	if strings.Contains(string(body), agentJWT) {
+		w.WriteHeader(200)
+		w.Write([]byte(authenticatedUser))
+		return
+	}
+	w.WriteHeader(401)
+	w.Write([]byte(unauthenticatedUser))
+	return
+}