go-examples/photoblog/admin/admin.go

package admin

import (
	"crypto/hmac"
	"crypto/sha256"
	"errors"
	"fmt"
	"html/template"
	"io/ioutil"
	"log"
	"net/http"
	"os"
	"path/filepath"

	"github.com/gorilla/sessions"
)

type AuthCookie struct {
	Templates      *template.Template
	Store          *sessions.CookieStore
	DataDir        *os.File
	PasswordSecret string
}

func (app *AuthCookie) LoginPage(res http.ResponseWriter, req *http.Request) {
	formErr := make(map[string]error)
	switch req.Method {
	case "POST":
		username := req.FormValue("username")
		formErr["username"] = app.VerifyUsername(username)
		formErr["password"] = app.VerifyPassword(username, req.FormValue("password"), res, req)
		if formErr["username"] == nil && formErr["password"] == nil {
			app.SaveUsername(username, res, req)
			RedirectHome(res, req)
			return
		}
		fallthrough
	case "GET":
		app.Templates.ExecuteTemplate(res, "login.html", formErr)
	}
}
func (app *AuthCookie) LogoutPage(res http.ResponseWriter, req *http.Request) {
	app.SaveUsername("", res, req)
	RedirectHome(res, req)
}
func (app *AuthCookie) VerifyUsername(username string) error {
	if username == "" {
		return errors.New("Empty username")
	}
	return nil
}
func (app *AuthCookie) VerifyPassword(username, password string, res http.ResponseWriter, req *http.Request) error {
	if password == "" {
		return errors.New("Empty password")
	}
	passfile, err := os.Open(filepath.Join(app.DataDir.Name(), username, ".password"))
	if err != nil {
		log.Println("Cannot open password file", err)
		return errors.New("Authentification failed")
	}
	defer passfile.Close()

	if username == "" {
		return nil
	}
	expected, err := ioutil.ReadAll(passfile)
	if err != nil {
		log.Println("Cannot read password file", err)
		return errors.New("Authentification failed")
	}
	expectedStr := string(expected)
	var expectedMAC []byte
	fmt.Sscanf(expectedStr, "%x", &expectedMAC)
	mac := hmac.New(sha256.New, []byte(app.PasswordSecret))
	mac.Write([]byte(password))
	passwordMAC := mac.Sum(nil)
	if !hmac.Equal(passwordMAC, expectedMAC) {
		log.Printf("Unmatched password for %s: %x - %x\n", username, passwordMAC, expectedMAC)
		return errors.New("Authentification failed")
	}
	log.Printf("Authentification successful")
	return nil
}
func (app *AuthCookie) CurrentSession(res http.ResponseWriter, req *http.Request) *sessions.Session {
	session, _ := app.Store.Get(req, "session")
	return session
}
func (app *AuthCookie) SaveUsername(username string, res http.ResponseWriter, req *http.Request) {
	session := app.CurrentSession(res, req)
	session.Values["username"] = username
	session.Save(req, res)
}
func (app *AuthCookie) IsLoggedIn(res http.ResponseWriter, req *http.Request) bool {
	session := app.CurrentSession(res, req)
	return session != nil && session.Values["username"] != ""
}
func (app *AuthCookie) Username(res http.ResponseWriter, req *http.Request) string {
	session := app.CurrentSession(res, req)
	if session == nil {
		return ""
	}
	return session.Values["username"].(string)
}
func RedirectHome(res http.ResponseWriter, req *http.Request) {
	http.Redirect(res, req, "/", http.StatusSeeOther)
}