使用JWT进行认证

JSON Web Tokens (JWT) are a more modern approach to authentication.

As the web moves to a greater separation between the client and server, JWT provides a wonderful alternative to traditional cookie based authentication models.

JWTs provide a way for clients to authenticate every request without having to maintain a session or repeatedly pass login credentials to the server.

用户注册之后, 服务器生成一个 JWT token返回给浏览器, 浏览器向服务器请求数据时将 JWT token 发给服务器, 服务器用 signature 中定义的方式解码

JWT 获取用户信息.

一个 JWT token包含3部分:
1 header: 告诉我们使用的算法和 token 类型
2 Payload: 必须使用 sub key 来指定用户 ID, 还可以包括其他信息比如 email, username 等.
3 Signature: 用来保证 JWT 的真实性. 可以使用不同算法

package main

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

	"github.com/codegangsta/negroni"
	"github.com/dgrijalva/jwt-go"
	"github.com/dgrijalva/jwt-go/request"
)
const (
	SecretKey = "welcome ---------"
)

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

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"`
}

func StartServer() {

	http.HandleFunc("/login", LoginHandler)

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

	log.Println("Now listening...")
	http.ListenAndServe(":8087", nil)
}

func main() {
	StartServer()
}

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

	err := json.NewDecoder(r.Body).Decode(&user)

	if err != nil {
		w.WriteHeader(http.StatusForbidden)
		fmt.Fprint(w, "Error in request")
		return
	}

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

	token := jwt.New(jwt.SigningMethodHS256)
	claims := make(jwt.MapClaims)
	claims["exp"] = time.Now().Add(time.Hour * time.Duration(1)).Unix()
	claims["iat"] = time.Now().Unix()
	token.Claims = claims

	if err != nil {
		w.WriteHeader(http.StatusInternalServerError)
		fmt.Fprintln(w, "Error extracting the key")
		fatal(err)
	}

	tokenString, err := token.SignedString([]byte(SecretKey))
	if err != nil {
		w.WriteHeader(http.StatusInternalServerError)
		fmt.Fprintln(w, "Error while signing the token")
		fatal(err)
	}

	response := Token{tokenString}
	JsonResponse(response, w)

}

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

	token, err := request.ParseFromRequest(r, request.AuthorizationHeaderExtractor,
		func(token *jwt.Token) (interface{}, error) {
			return []byte(SecretKey), 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, "Unauthorized access to this resource")
	}

}

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)
}

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