JSON Web Tokens in Go

jwt_golang_example.go

package main

import (
	"io/ioutil"
	"log"
	"strings"
	"net/http"
	"encoding/json"
	"fmt"
	"time"

	"github.com/codegangsta/negroni"
	"github.com/dgrijalva/jwt-go"
	"os"
)


//RSA KEYS AND INITIALISATION


const (
	privKeyPath = "path/to/keys/app.rsa"
	pubKeyPath = "path/to/keys/app.rsa.pub"
)

var VerifyKey, SignKey []byte


func initKeys(){
	var err error

	SignKey, err = ioutil.ReadFile(privKeyPath)
	if err != nil {
		log.Fatal("Error reading private key")
		return
	}

	VerifyKey, err = ioutil.ReadFile(pubKeyPath)
	if err != nil {
		log.Fatal("Error reading public key")
		return
	}
}



//STRUCT DEFINITIONS


type UserCredentials struct {
	Username	string  `json:"username"`
	Password	string	`json:"password"`
}

type User struct {
	ID			int 	`json:"id"`
	Name		string  `json:"name"`
	Username	string  `json:"username"`
	Password	string	`json:"password"`
}

type Response struct {
	Data	string	`json:"data"`
}

type Token struct {
	Token 	string    `json:"token"`
}



//SERVER ENTRY POINT


func StartServer(){

	//PUBLIC ENDPOINTS
	http.HandleFunc("/login", LoginHandler)

	//PROTECTED ENDPOINTS
	http.Handle("/resource/", negroni.New(
		negroni.HandlerFunc(ValidateTokenMiddleware),
		negroni.Wrap(http.HandlerFunc(ProtectedHandler)),
	))

	log.Println("Now listening...")
	http.ListenAndServe(":8000", nil)
}

func main() {

	initKeys()
	StartServer()
}


//////////////////////////////////////////


/////////////ENDPOINT HANDLERS////////////


/////////////////////////////////////////


func ProtectedHandler(w http.ResponseWriter, r *http.Request){

	response := Response{"Gained access to protected resource"}
	JsonResponse(response, w)

}

func LoginHandler(w http.ResponseWriter, r *http.Request) {

	var user UserCredentials

	//decode request into UserCredentials struct
	err := json.NewDecoder(r.Body).Decode(&user)
	if err != nil {
		w.WriteHeader(http.StatusForbidden)
		fmt.Fprintf(w, "Error in request")
		return
	}

	fmt.Println(user.Username, user.Password)

	//validate user credentials
	if strings.ToLower(user.Username) != "alexcons" {
		if user.Password != "kappa123" {
			w.WriteHeader(http.StatusForbidden)
			fmt.Println("Error logging in")
			fmt.Fprint(w, "Invalid credentials")
			return
		}
	}

	//create a rsa 256 signer
	signer := jwt.New(jwt.GetSigningMethod("RS256"))

	//set claims
	signer.Claims["iss"] = "admin"
	signer.Claims["exp"] = time.Now().Add(time.Minute * 20).Unix()
	signer.Claims["CustomUserInfo"] = struct {
		Name	string
		Role	string
	}{user.Username, "Member"}

	tokenString, err := signer.SignedString(SignKey)

	if err != nil {
		w.WriteHeader(http.StatusInternalServerError)
		fmt.Fprintln(w, "Error while signing the token")
		log.Printf("Error signing token: %v\n", err)
	}

	//create a token instance using the token string
	response := Token{tokenString}
	JsonResponse(response, w)

}



//AUTH TOKEN VALIDATION


func ValidateTokenMiddleware(w http.ResponseWriter, r *http.Request, next http.HandlerFunc) {

	//validate token
	token, err := jwt.ParseFromRequest(r, func(token *jwt.Token) (interface{}, error){
		return VerifyKey, nil
	})

	if err == nil {

		if token.Valid{
			next(w, r)
		} else {
			w.WriteHeader(http.StatusUnauthorized)
			fmt.Fprint(w, "Token is not valid")
		}
	} else {
		w.WriteHeader(http.StatusUnauthorized)
		fmt.Fprint(w, "Unauthorised access to this resource")
	}

}



//HELPER FUNCTIONS


func JsonResponse(response interface{}, w http.ResponseWriter) {

	json, err :=  json.Marshal(response)
	if err != nil {
		http.Error(w, err.Error(), http.StatusInternalServerError)
		return
	}

	w.WriteHeader(http.StatusOK)
	w.Header().Set("Content-Type", "application/json")
	w.Write(json)
}

This code is obsolete now. Please update for go-jwt 3.0. As you said in your video a simple tutorial like this is so rare to find!

	if strings.ToLower(user.Username) != "alexcons" {
		if user.Password != "kappa123" {
			w.WriteHeader(http.StatusForbidden)
			fmt.Println("Error logging in")
			fmt.Fprint(w, "Invalid credentials")
			return
		}
	}

if username is other than alexcons it will also pass :(

the example should change something:

• remove os package and add "github.com/dgrijalva/jwt-go/request"
• change LoginHandler
• change ValidateTokenMiddleware

the whole code:
`package main

import (
"encoding/json"
"fmt"
"io/ioutil"
"log"
"net/http"
"strings"
"time"

"github.com/codegangsta/negroni"
"github.com/dgrijalva/jwt-go"
"github.com/dgrijalva/jwt-go/request"

)

//RSA KEYS AND INITIALISATION

const (
privKeyPath = "path/to/keys/app.rsa"
pubKeyPath = "path/to/keys/app.rsa.pub"
)

var VerifyKey, SignKey []byte

func initKeys() {
var err error

SignKey, err = ioutil.ReadFile(privKeyPath)
if err != nil {
	log.Fatal("Error reading private key")
	return
}

VerifyKey, err = ioutil.ReadFile(pubKeyPath)
if err != nil {
	log.Fatal("Error reading public key")
	return
}

}

//STRUCT DEFINITIONS

type UserCredentials struct {
Username string json:"username"
Password string json:"password"
}

type User struct {
ID int json:"id"
Name string json:"name"
Username string json:"username"
Password string json:"password"
}

type Response struct {
Data string json:"data"
}

type Token struct {
Token string json:"token"
}

//SERVER ENTRY POINT

func StartServer() {

//PUBLIC ENDPOINTS
http.HandleFunc("/login", LoginHandler)

//PROTECTED ENDPOINTS
http.Handle("/resource/", negroni.New(
	negroni.HandlerFunc(ValidateTokenMiddleware),
	negroni.Wrap(http.HandlerFunc(ProtectedHandler)),
))

log.Println("Now listening...")
http.ListenAndServe(":8000", nil)

}

func main() {

initKeys()
StartServer()

}

//////////////////////////////////////////

/////////////ENDPOINT HANDLERS////////////

/////////////////////////////////////////

func ProtectedHandler(w http.ResponseWriter, r *http.Request) {

response := Response{"Gained access to protected resource"}
JsonResponse(response, w)

}

func LoginHandler(w http.ResponseWriter, r *http.Request) {

var user UserCredentials

//decode request into UserCredentials struct
err := json.NewDecoder(r.Body).Decode(&user)
if err != nil {
	w.WriteHeader(http.StatusForbidden)
	fmt.Fprintf(w, "Error in request")
	return
}

fmt.Println(user.Username, user.Password)

//validate user credentials
if strings.ToLower(user.Username) != "alexcons" {
	if user.Password != "kappa123" {
		w.WriteHeader(http.StatusForbidden)
		fmt.Println("Error logging in")
		fmt.Fprint(w, "Invalid credentials")
		return
	}
}

//create a rsa 256 signer
signer := jwt.New(jwt.GetSigningMethod("RS256"))

//set claims
claims := make(jwt.MapClaims)
claims["iss"] = "admin"
claims["exp"] = time.Now().Add(time.Minute * 20).Unix()
claims["CustomUserInfo"] = struct {
	Name string
	Role string
}{user.Username, "Member"}
signer.Claims = claims

tokenString, err := signer.SignedString(SignKey)

if err != nil {
	w.WriteHeader(http.StatusInternalServerError)
	fmt.Fprintln(w, "Error while signing the token")
	log.Printf("Error signing token: %v\n", err)
}

//create a token instance using the token string
response := Token{tokenString}
JsonResponse(response, w)

}

//AUTH TOKEN VALIDATION

func ValidateTokenMiddleware(w http.ResponseWriter, r *http.Request, next http.HandlerFunc) {

//validate token
token, err := request.ParseFromRequest(r, request.AuthorizationHeaderExtractor,
	func(token *jwt.Token) (interface{}, error) {
		return VerifyKey, nil
	})

if err == nil {

	if token.Valid {
		next(w, r)
	} else {
		w.WriteHeader(http.StatusUnauthorized)
		fmt.Fprint(w, "Token is not valid")
	}
} else {
	w.WriteHeader(http.StatusUnauthorized)
	fmt.Fprint(w, "Unauthorised access to this resource")
}

}

//HELPER FUNCTIONS

func JsonResponse(response interface{}, w http.ResponseWriter) {

json, err := json.Marshal(response)
if err != nil {
	http.Error(w, err.Error(), http.StatusInternalServerError)
	return
}

w.WriteHeader(http.StatusOK)
w.Header().Set("Content-Type", "application/json")
w.Write(json)

}
`

@wangshubo1989 Thank you!

I get this error when I do a POST on login:

• Error signing token: key is invalid

can someone tell me why ?

I found

you need to remove this :

//create a rsa 256 signer
	signer := jwt.New(jwt.GetSigningMethod("RS256"))

	//set claims
	
	claims := make(jwt.MapClaims)
	claims["iss"] = "admin"
	claims["exp"] = time.Now().Add(time.Minute * 20).Unix()
	claims["CustomUserInfo"] = struct {
		Name string
		Role string
	}{user.Username, "Member"}
	signer.Claims = claims

tokenString, err := signer.SignedString(SignKey)

and use this instead :

token := jwt.NewWithClaims(jwt.SigningMethodHS256, jwt.MapClaims{
		"iss": "admin",
		"exp": time.Now().Add(time.Minute * 20).Unix(),
		"CustomUserInfo": struct {
			Name string
			Role string
		}{user.Username, "Member"},
	})

tokenString, err := token.SignedString(SignKey)

@Clement-Jean Thanks! Your change makes everything work 👍

I found

you need to remove this :

//create a rsa 256 signer
	signer := jwt.New(jwt.GetSigningMethod("RS256"))

	//set claims
	
	claims := make(jwt.MapClaims)
	claims["iss"] = "admin"
	claims["exp"] = time.Now().Add(time.Minute * 20).Unix()
	claims["CustomUserInfo"] = struct {
		Name string
		Role string
	}{user.Username, "Member"}
	signer.Claims = claims

tokenString, err := signer.SignedString(SignKey)

and use this instead :

token := jwt.NewWithClaims(jwt.SigningMethodHS256, jwt.MapClaims{
		"iss": "admin",
		"exp": time.Now().Add(time.Minute * 20).Unix(),
		"CustomUserInfo": struct {
			Name string
			Role string
		}{user.Username, "Member"},
	})

tokenString, err := token.SignedString(SignKey)

Hi, thanks a lot! But it seems you are using HMAC signing method instead of the original RSA. I still got key is invalid error when using RSA method. Could you check if the RSA signing method works for you?

// needed to Parse before signing for me
signKey, err := jwt.ParseRSAPrivateKeyFromPEM(SignKey)
if err != nil {
log.Println(err)
}

tokenString, err := token.SignedString(signKey)

Hi,
I have an issue.

My login endpoint is working after using the jwt.ParseRSAPrivateKeyFromPEM() function, it is creating the token but when i am using the token for '/resource' end-point, the response i get is "Unauthorised access to resource".

Can you help me with this??