oauth-guard/oauth.go

package main

import (
	"crypto/rand"
	_ "embed"
	"encoding/base64"
	"encoding/json"
	"html/template"
	"net/http"
	"sync"
	"time"

	"github.com/google/uuid"
	"golang.org/x/oauth2"
)

type Session struct {
	ID        string    `json:"id"`
	UserID    string    `json:"user_id"`
	ExpiresAt time.Time `json:"expires_at"`
	CreatedAt time.Time `json:"created_at"`
}

const SessionCookie = "session"

type OAuthStore struct {
	sessions map[string]*Session
	mutex    sync.RWMutex
	oa2      *oauth2.Config
	config   *Config
}

func NewSessionStore(config *Config, oa2 *oauth2.Config) *OAuthStore {
	return &OAuthStore{
		sessions: make(map[string]*Session),
		oa2:      oa2,
		config:   config,
	}
}

func (s *OAuthStore) CreateSession(userID string, duration time.Duration) (*Session, error) {
	uid, err := uuid.NewRandom()
	if err != nil {
		return nil, err
	}
	id := uid.String()

	session := &Session{
		ID:        id,
		UserID:    userID,
		ExpiresAt: time.Now().Add(duration),
		CreatedAt: time.Now(),
	}

	s.mutex.Lock()
	s.sessions[id] = session
	s.mutex.Unlock()

	return session, nil
}

func (s *OAuthStore) GetSession(sessionID string) (*Session, bool) {
	s.mutex.RLock()
	defer s.mutex.RUnlock()

	session, exists := s.sessions[sessionID]
	if !exists {
		return nil, false
	}
	if session.ExpiresAt.Before(time.Now()) {
		s.DeleteSession(sessionID)
		return nil, false
	}
	return session, true

}

func (s *OAuthStore) DeleteSession(sessionID string) {
	s.mutex.Lock()
	delete(s.sessions, sessionID)
	s.mutex.Unlock()
}

func sendToLoginPage(w http.ResponseWriter, r *http.Request) {
	http.Redirect(w, r, "/oauth/login", http.StatusTemporaryRedirect)
}
func generateRandomToken() string {
	b := make([]byte, 32)
	rand.Read(b)
	return base64.StdEncoding.EncodeToString(b)
}

//go:embed templates/LoginPage.html
var loginPageContent string

func (s *OAuthStore) LoginPage() http.Handler {

	loginPageTemplate := template.Must(template.New("loginPageContent").Parse(loginPageContent))

	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		state := generateRandomToken()

		if cookie, err := r.Cookie("oauth_state"); err == nil && cookie.Value != "" {
			state = cookie.Value
		} else {
			http.SetCookie(w, &http.Cookie{
				Name:     "oauth_state",
				Value:    state,
				HttpOnly: true,
				Secure:   true, // Set to true in production
				SameSite: http.SameSiteLaxMode,
				MaxAge:   60 * 10, // 10 minutes
			})
		}

		url := s.oa2.AuthCodeURL(state)

		provider := s.config.OAuthProvider.Kind
		switch provider {
		case "google":
			provider = "Google"
		case "github":
			provider = "GitHub"
		}

		loginPageTemplate.Execute(w, struct {
			Url      string
			State    string
			Provider string
		}{
			Url:      url,
			State:    state,
			Provider: provider,
		})
	})
}

func (s *OAuthStore) Protected(next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {

		cookie, err := r.Cookie(SessionCookie)
		if err != nil {
			sendToLoginPage(w, r)
			return
		}
		sess, exists := s.GetSession(cookie.Value)
		if !exists {
			sendToLoginPage(w, r)
			return
		}

		found := false
		for _, user := range s.config.AllowedUsers {
			if user == sess.UserID {
				found = true
			}
		}
		if !found {
			sendToLoginPage(w, r)
			return
		}

		next.ServeHTTP(w, r)
	})
}

func (s *OAuthStore) CallbackHandler() http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		stateCookie, err := r.Cookie("oauth_state")
		if err != nil || stateCookie.Value != r.URL.Query().Get("state") {
			http.Error(w, "Invalid state", http.StatusBadRequest)
			return
		}

		tok, err := s.oa2.Exchange(r.Context(), r.URL.Query().Get("code"))
		if err != nil {
			http.Error(w, "Failed to exchange token", http.StatusInternalServerError)
			return
		}
		userID, err := getUserInfo(s.config.OAuthProvider.Kind, tok.AccessToken)
		if err != nil {
			http.Error(w, "Failed to get info", http.StatusInternalServerError)
			return
		}
		sess, err := s.CreateSession(userID, time.Hour*24)
		if err != nil {
			http.Error(w, "Failed to create session", http.StatusInternalServerError)
			return
		}

		http.SetCookie(w, &http.Cookie{
			Name:     SessionCookie,
			Value:    sess.ID,
			HttpOnly: true,
			Secure:   true,
			SameSite: http.SameSiteLaxMode,
			MaxAge:   int(time.Hour.Seconds() * 24),
			Path:     "/",
		})

		// clear cookie
		http.SetCookie(w, &http.Cookie{
			Name:   "oauth_state",
			Value:  "",
			MaxAge: -1,
		})

		// TODO: remember what path the user was on and redirect them back there after doing the whole login process
		http.Redirect(w, r, "/", http.StatusTemporaryRedirect)
	})
}

func getUserInfo(providerKind, token string) (string, error) {
	switch providerKind {
	case "google":
		type UserInfo struct {
			ID    string `json:"sub"`
			Email string `json:"email"`
			Name  string `json:"name"`
		}
		resp, err := http.Get("https://www.googleapis.com/oauth2/v2/userinfo?access_token=" + token)
		if err != nil {
			return "", err
		}
		defer resp.Body.Close()

		var userInfo UserInfo
		if err := json.NewDecoder(resp.Body).Decode(&userInfo); err != nil {
			return "", err
		}

		return userInfo.Email, nil
	case "github":
		type UserInfo struct {
			Login string `json:"login"`
			Name  string `json:"name"`
		}
		req, _ := http.NewRequest("GET", "https://api.github.com/user", nil)
		req.Header.Add("Authorization", "Bearer "+token)
		resp, err := http.DefaultClient.Do(req)
		if err != nil {
			return "", err
		}
		defer resp.Body.Close()

		var userInfo UserInfo
		if err := json.NewDecoder(resp.Body).Decode(&userInfo); err != nil {
			return "", err
		}
		return userInfo.Login, nil
	default:
		panic("unimplemented")
	}
}