added okta-resource server example to project

.gitignore

@@ -13,6 +13,7 @@
 
 # misc
 .DS_Store
+.env
 .env.local
 .env.development.local
 .env.test.local

server/.env.dist

+CLIENT_ID=dev-91882654.okta.com
+SPA_CLIENT_ID=0oa1f4zfeiiZPB6DF5d7
+ISSUER=https://dev-91882654.okta.com/oauth2/default

server/main.go

+package main
+
+import (
+	"encoding/json"
+	"fmt"
+	"log"
+	"net/http"
+	"os"
+	"strings"
+
+	verifier "github.com/okta/okta-jwt-verifier-golang"
+	oktaUtils "github.com/okta/samples-golang/resource-server/utils"
+)
+
+func main() {
+	oktaUtils.ParseEnvironment()
+
+	http.HandleFunc("/", HomeHandler)
+	http.HandleFunc("/api/messages", ApiMessagesHandler)
+
+	log.Print("server starting at localhost:3030 ... ")
+	err := http.ListenAndServe("localhost:3030", nil)
+	if err != nil {
+		log.Printf("the HTTP server failed to start: %s", err)
+		os.Exit(1)
+	}
+}
+
+func HomeHandler(w http.ResponseWriter, r *http.Request) {
+	fmt.Fprintln(w, "Resource server started, please start front-end application")
+}
+
+func ApiMessagesHandler(w http.ResponseWriter, r *http.Request) {
+	w.Header().Add("Access-Control-Allow-Origin", "*")
+	w.Header().Add("Access-Control-Allow-Headers", "Content-Type, authorization")
+	w.Header().Add("Access-Control-Allow-Methods", "GET, POST,OPTIONS")
+
+	if r.Method == "OPTIONS" {
+		return
+	}
+
+	if !isAuthenticated(r) {
+		w.WriteHeader(http.StatusUnauthorized)
+		w.Write([]byte("401 - You are not authorized for this request"))
+		return
+	}
+
+	m1 := Message{1522272240, "I am a robot."}
+	m2 := Message{1522268640, "Hello, World!"}
+	allMessages := []Message{}
+	allMessages = append(allMessages, m1)
+	allMessages = append(allMessages, m2)
+
+	mess := Messages{
+		allMessages,
+	}
+
+	w.WriteHeader(http.StatusOK)
+	w.Header().Set("Content-Type", "application/json")
+	json.NewEncoder(w).Encode(mess)
+}
+
+type Message struct {
+	Date float64 `json:"date"`
+	Text string  `json:"text"`
+}
+
+type Messages struct {
+	MessageList []Message `json:"messages"`
+}
+
+func isAuthenticated(r *http.Request) bool {
+	authHeader := r.Header.Get("Authorization")
+
+	if authHeader == "" {
+		return false
+	}
+	tokenParts := strings.Split(authHeader, "Bearer ")
+	bearerToken := tokenParts[1]
+
+	tv := map[string]string{}
+	tv["aud"] = "api://default"
+	tv["cid"] = os.Getenv("SPA_CLIENT_ID")
+	jv := verifier.JwtVerifier{
+		Issuer:           os.Getenv("ISSUER"),
+		ClaimsToValidate: tv,
+	}
+
+	_, err := jv.New().VerifyAccessToken(bearerToken)
+	if err != nil {
+		return false
+	}
+
+	return true
+}

server/utils/nonce.go

+package utils
+
+import (
+	"crypto/rand"
+	"encoding/base64"
+	"fmt"
+)
+
+func GenerateNonce() (string, error) {
+	nonceBytes := make([]byte, 32)
+	_, err := rand.Read(nonceBytes)
+	if err != nil {
+		return "", fmt.Errorf("could not generate nonce")
+	}
+
+	return base64.URLEncoding.EncodeToString(nonceBytes), nil
+}

server/utils/parseEnv.go

+package utils
+
+import (
+	"bufio"
+	"log"
+	"os"
+	"strings"
+)
+
+func ParseEnvironment() {
+	// useGlobalEnv := true
+	if _, err := os.Stat(".env"); os.IsNotExist(err) {
+		log.Printf("Environment Variable file (.env) is not present.  Relying on Global Environment Variables")
+		// useGlobalEnv = false
+	}
+
+	setEnvVariable("CLIENT_ID", os.Getenv("CLIENT_ID"))
+	setEnvVariable("SPA_CLIENT_ID", os.Getenv("SPA_CLIENT_ID"))
+	setEnvVariable("ISSUER", os.Getenv("ISSUER"))
+
+	if os.Getenv("CLIENT_ID") == "" {
+		log.Printf("Could not resolve a CLIENT_ID environment variable.")
+		os.Exit(1)
+	}
+
+	if os.Getenv("SPA_CLIENT_ID") == "" {
+		log.Printf("Could not resolve a SPA_CLIENT_ID environment variable.")
+		os.Exit(1)
+	}
+
+	if os.Getenv("ISSUER") == "" {
+		log.Printf("Could not resolve a ISSUER environment variable.")
+		os.Exit(1)
+	}
+}
+
+func setEnvVariable(env string, current string) {
+	if current != "" {
+		return
+	}
+
+	file, _ := os.Open(".env")
+	defer file.Close()
+
+	lookInFile := bufio.NewScanner(file)
+	lookInFile.Split(bufio.ScanLines)
+
+	for lookInFile.Scan() {
+		parts := strings.Split(lookInFile.Text(), "=")
+		key, value := parts[0], parts[1]
+		if key == env {
+			os.Setenv(key, value)
+		}
+	}
+}