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"
)

const (
	USER      = "username"
	PWD       = "password"
	SESS_USER = "username"
	SESSION   = "photoblog.session"
)

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

// Verify Username
func (app *AuthCookie) VerifyUsername(username string) error {
	if username == "" {
		return errors.New("Empty username")
	}
	return nil
}

// Verify password for user, check with file
func (app *AuthCookie) VerifyPassword(username, password string, res http.ResponseWriter, req *http.Request) error {
	if password == "" {
		return errors.New("Empty password")
	}
	if username == "" {
		return nil
	}
	// open password file
	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()

	// read password file
	expected, err := ioutil.ReadAll(passfile)
	if err != nil {
		log.Println("Cannot read password file", err)
		return errors.New("Authentification failed")
	}
	// hash password and compare
	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 (" + username + ")")
	return nil
}

// Save username in session
func (app *AuthCookie) SaveUsername(username string, res http.ResponseWriter, req *http.Request) {
	session := app.CurrentSession(res, req)
	session.Values[SESS_USER] = username
	session.Save(req, res)
}

// Test if a user is logged in
func (app *AuthCookie) IsLoggedIn(res http.ResponseWriter, req *http.Request) bool {
	session := app.CurrentSession(res, req)
	return session != nil && session.Values[SESS_USER] != ""
}

// Current username (from session cookie)
func (app *AuthCookie) Username(res http.ResponseWriter, req *http.Request) string {
	session := app.CurrentSession(res, req)
	if session == nil {
		return ""
	}
	val, _ := session.Values[SESS_USER].(string)
	return val
}

// Current session
func (app *AuthCookie) CurrentSession(res http.ResponseWriter, req *http.Request) *sessions.Session {
	session, _ := app.Store.Get(req, SESSION)
	return session
}

// Redirect to home page
func (app *AuthCookie) RedirectHome(res http.ResponseWriter, req *http.Request) {
	http.Redirect(res, req, "/", http.StatusSeeOther)
}

// ROUTES //

// login: form
func (app *AuthCookie) LoginPage(res http.ResponseWriter, req *http.Request) {
	formErr := make(map[string]error)
	if req.Method == http.MethodPost {
		username := req.FormValue(USER)
		formErr[USER] = app.VerifyUsername(username)
		formErr[PWD] = app.VerifyPassword(username, req.FormValue(PWD), res, req)
		if formErr[USER] == nil && formErr[PWD] == nil {
			app.SaveUsername(username, res, req)
			app.RedirectHome(res, req)
			return
		}
	}
	app.Templates.ExecuteTemplate(res, "login.html", formErr)
}

// logout: delete session and redirect to home
func (app *AuthCookie) LogoutPage(res http.ResponseWriter, req *http.Request) {
	app.SaveUsername("", res, req)
	app.RedirectHome(res, req)
}