main.go

//original code by @Elliot_f of Tutorial Edge youtube channel: https://www.youtube.com/watch?v=-Scg9INymBs
//some adaptations to use with gorilla/mux 

package main

import (
	"encoding/json"
	"fmt"
	jwt "github.com/dgrijalva/jwt-go"
	"github.com/gorilla/mux"
	"log"
	"net/http"
	"time"
)

var mySigningKey = []byte("mysupersecretphrase")

func GenerateJWT() (string, error) {
	token := jwt.New(jwt.SigningMethodHS256)
	claims := token.Claims.(jwt.MapClaims)
	claims["authorized"] = true
	claims["user"] = "Fabio Souza"
	claims["exp"] = time.Now().Add(time.Minute * 30).Unix()

	tokenString, err := token.SignedString(mySigningKey)

	if err != nil {
		log.Fatal(err)
		return "", err
	}

	return tokenString, nil
}

func isAuthorized(next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		if r.Header["Token"] != nil {
			token, err := jwt.Parse(r.Header["Token"][0], func(token *jwt.Token) (interface{}, error) {
				if _, ok := token.Method.(*jwt.SigningMethodHMAC); !ok {
					return nil, fmt.Errorf("There was an error")
				}
				return mySigningKey, nil
			})

			if err != nil {
				fmt.Fprintf(w, err.Error())
			}

			if token.Valid {
				next.ServeHTTP(w, r)
			}

		} else {
			fmt.Fprintf(w, "Not Authorized")
		}

	})
}

func getAllUsers(w http.ResponseWriter, r *http.Request) {
	w.Header().Set("Content-Type", "application/json")

	fmt.Fprintf("Get Users endpoint")
}

func main() {
  
  router := mux.NewRouter()

	tokenString, err := GenerateJWT()

	if err != nil {
		log.Fatal(err)
	}

	fmt.Println(tokenString)

	//Router without middleware
	router.Path("/api/user").Methods("POST").Handler(http.HandlerFunc(createUser))

	api := router.PathPrefix("/api").Subrouter()

	api.Use(isAuthorized)

	// Router Handlers / Endpoints
	api.Path("/users").Methods("GET").Handler(http.HandlerFunc(getUsers))
	log.Fatal(http.ListenAndServe(":8000", router))

}