feat(backend): Discord OAuth login with DB-backed sessions (#23)

The browser UI signs in with a Discord authorization code grant (identify + guilds.members.read) instead of a shared password. Guild membership is the gate; the owner's Discord ID is the only identity allowed in while registration is closed. Sessions become rows in a sessions table with opaque random ids — the cookie carries only the id, looked up and expiry-checked per request — so deleting a row revokes a session. HMAC cookie signing, its derived key, and WEB_PASSWORD are gone, and no replacement signing secret is introduced (ADR-0002). Discord's API base is configurable (DISCORD_API_BASE); the full flow is tested through the real router against a local stub, including the form-encoded token exchange Discord rejects if sent as JSON.
2026-08-08 08:31:46 +07:00
parent 8cebb94b92
commit 13e8e73da7
19 changed files with 1272 additions and 357 deletions
@@ -1,7 +1,7 @@
 package web

 import (
-	"crypto/subtle"
+	"context"
 	"embed"
 	"html/template"
 	"io/fs"
@@ -31,14 +31,18 @@ const RecentCount = 5
 // It is a separate handler from api.Handler because the two speak different
 // representations (HTML versus JSON) to different clients under different auth.
 type Handler struct {
-	store    *store.Store
-	// readerID is the Reader this UI acts as — the seeded owner, while the web
-	// password is still the only credential (issue #22).
+	store *store.Store
+	// readerID is the owner Reader's id, the only Reader that can exist
+	// while registration is closed (issue #23). Every session row points at
+	// it, so it is also the Reader the UI acts as.
 	readerID int64
 	tmpl     *template.Template
-	key      []byte
-	password string
+	discord  DiscordConfig
+	states   *oauthStates
 	limiter  *session.LoginLimiter
+	// httpClient is the plain stdlib client that talks to Discord. It is not
+	// an injected interface: tests point APIBBase at a stub server instead.
+	httpClient *http.Client
 }

 // listView is what every list-rendering template receives.
@@ -46,7 +50,7 @@ type listView struct {
 	// Lib is the library this view renders: store.KindManga or store.KindNovel.
 	// Manga is the default and carries no query parameter, so every pre-novel
 	// URL keeps meaning exactly what it did.
-	Lib string
+	Lib    string
 	Tab    string // "all", "fav", or "new"
 	Recent []store.Bookmark
 	Items  []store.Bookmark
@@ -84,24 +88,26 @@ type loginView struct {

 // New parses every template up front so a broken one kills the process at
 // startup rather than the first request that touches it.
-func New(s *store.Store, readerID int64, apiToken, webPassword string) (*Handler, error) {
+func New(s *store.Store, readerID int64, discord DiscordConfig) (*Handler, error) {
 	tmpl, err := template.ParseFS(templateFS, "templates/*.html")
 	if err != nil {
 		return nil, err
 	}
 	return &Handler{
-		store:    s,
-		readerID: readerID,
-		tmpl:     tmpl,
-		key:      session.Key(apiToken, webPassword),
-		password: webPassword,
-		limiter:  session.NewLoginLimiter(),
+		store:      s,
+		readerID:   readerID,
+		tmpl:       tmpl,
+		discord:    discord,
+		states:     newOAuthStates(),
+		limiter:    session.NewLoginLimiter(),
+		httpClient: &http.Client{Timeout: discordTimeout},
 	}, nil
 }

 func (h *Handler) Register(mux *http.ServeMux) {
 	mux.HandleFunc("GET /{$}", h.index)
-	mux.HandleFunc("POST /login", h.login)
+	mux.HandleFunc("GET /auth/discord", h.discordStart)
+	mux.HandleFunc("GET /auth/discord/callback", h.discordCallback)
 	mux.HandleFunc("POST /logout", h.logout)
 	mux.Handle("GET /static/", staticHandler())

@@ -135,10 +141,26 @@ func staticHandler() http.Handler {
 		}))
 }

-// authed reports whether the request carries a valid session cookie.
-func (h *Handler) authed(r *http.Request) bool {
+type ctxKey int
+
+// readerCtxKey is where requireSession stashes the authenticated Reader id.
+const readerCtxKey ctxKey = iota
+
+// sessionReader reports whether the request carries a live session, and for
+// whom. The cookie holds only the session id; the row behind it is looked up
+// on every request, so deleting a session takes effect immediately. Expiry is
+// enforced here, in the store, which also removes rows that have lapsed.
+func (h *Handler) sessionReader(r *http.Request) (int64, bool) {
 	c, err := r.Cookie(session.CookieName)
-	return err == nil && session.Verify(h.key, c.Value, time.Now().UnixMilli())
+	if err != nil {
+		return 0, false
+	}
+	sess, ok, err := h.store.GetSession(c.Value, time.Now())
+	if err != nil {
+		log.Printf("session lookup: %v", err)
+		return 0, false
+	}
+	return sess.ReaderID, ok
 }

 // requireSession guards the fragment endpoints. It answers 401 rather than
@@ -146,14 +168,18 @@ func (h *Handler) authed(r *http.Request) bool {
 // redirected login page would be spliced into the card list.
 func (h *Handler) requireSession(next http.HandlerFunc) http.HandlerFunc {
 	return func(w http.ResponseWriter, r *http.Request) {
-		if !h.authed(r) {
+		readerID, ok := h.sessionReader(r)
+		if !ok {
 			http.Error(w, "unauthorized", http.StatusUnauthorized)
 			return
 		}
-		next(w, r)
+		next(w, r.WithContext(context.WithValue(r.Context(), readerCtxKey, readerID)))
 	}
 }

+// readerOf returns the authenticated Reader id requireSession stashed.
+func readerOf(r *http.Request) int64 { return r.Context().Value(readerCtxKey).(int64) }
+
 func (h *Handler) render(w http.ResponseWriter, status int, name string, data any) {
 	w.Header().Set("Content-Type", "text/html; charset=utf-8")
 	w.WriteHeader(status)
@@ -167,11 +193,12 @@ func (h *Handler) render(w http.ResponseWriter, status int, name string, data an
 // page is served at / with status 200 rather than as a redirect to a separate
 // URL: one page, no redirect loop to reason about.
 func (h *Handler) index(w http.ResponseWriter, r *http.Request) {
-	if !h.authed(r) {
+	readerID, ok := h.sessionReader(r)
+	if !ok {
 		h.render(w, http.StatusOK, "login", loginView{})
 		return
 	}
-	view, err := h.buildListView(libOf(r.URL.Query().Get("lib")), r.URL.Query().Get("tab"))
+	view, err := h.buildListView(readerID, libOf(r.URL.Query().Get("lib")), r.URL.Query().Get("tab"))
 	if err != nil {
 		log.Printf("index: %v", err)
 		http.Error(w, "internal error", http.StatusInternalServerError)
@@ -212,15 +239,15 @@ func libOf(q string) string {
 	return store.KindManga
 }

-// buildListView loads the list once and derives both the tab-filtered items and
-// the recent strip from it.
+// buildListView loads one reader's list once and derives both the tab-filtered
+// items and the recent strip from it.
 //
 // Archived and finished series appear in their own tab and nowhere else — not
 // in All, not in Updated, not in Favourites, and not in the recent strip. An
 // archived favourite therefore shows only under Archived: Favourites means
 // "favourites I am currently reading".
-func (h *Handler) buildListView(lib, tab string) (listView, error) {
-	all, err := h.store.List(h.readerID) // already ordered updated_at DESC
+func (h *Handler) buildListView(readerID int64, lib, tab string) (listView, error) {
+	all, err := h.store.List(readerID) // already ordered updated_at DESC
 	if err != nil {
 		return listView{}, err
 	}
@@ -271,7 +298,7 @@ func (h *Handler) buildListView(lib, tab string) (listView, error) {
 }

 func (h *Handler) uiList(w http.ResponseWriter, r *http.Request) {
-	view, err := h.buildListView(libOf(r.URL.Query().Get("lib")), r.URL.Query().Get("tab"))
+	view, err := h.buildListView(readerOf(r), libOf(r.URL.Query().Get("lib")), r.URL.Query().Get("tab"))
 	if err != nil {
 		log.Printf("ui list: %v", err)
 		http.Error(w, "internal error", http.StatusInternalServerError)
@@ -329,7 +356,7 @@ func (h *Handler) writeChromeOOB(w http.ResponseWriter, view listView) {
 // refreshChrome rebuilds the chrome for the reader's current tab after a
 // mutation and appends it to the response.
 func (h *Handler) refreshChrome(w http.ResponseWriter, r *http.Request) {
-	view, err := h.buildListView(currentLib(r), currentTab(r))
+	view, err := h.buildListView(readerOf(r), currentLib(r), currentTab(r))
 	if err != nil {
 		log.Printf("ui chrome: %v", err)
 		return
@@ -337,35 +364,21 @@ func (h *Handler) refreshChrome(w http.ResponseWriter, r *http.Request) {
 	h.writeChromeOOB(w, view)
 }

-func (h *Handler) login(w http.ResponseWriter, r *http.Request) {
-	ip := session.ClientIP(r)
-	if wait := h.limiter.RetryAfter(ip, time.Now()); wait > 0 {
-		secs := int(wait.Seconds()) + 1
-		w.Header().Set("Retry-After", strconv.Itoa(secs))
-		h.render(w, http.StatusTooManyRequests, "login", loginView{
-			Error: "Too many attempts. Try again in " +
-				strconv.Itoa((secs+59)/60) + " min.",
-		})
-		return
-	}
-
-	if err := r.ParseForm(); err != nil {
-		http.Error(w, "invalid form", http.StatusBadRequest)
-		return
-	}
-	got := r.PostFormValue("password")
-	if subtle.ConstantTimeCompare([]byte(got), []byte(h.password)) != 1 {
-		h.limiter.Fail(ip, time.Now())
-		h.render(w, http.StatusUnauthorized, "login", loginView{Error: "Wrong password."})
-		return
-	}
-
-	h.limiter.Reset(ip)
-	session.SetCookie(w, r, h.key)
-	http.Redirect(w, r, "/", http.StatusSeeOther)
+// renderLogin renders the login page with an error message, for refused or
+// failed sign-ins. Every message is author-written text — nothing Discord
+// supplied is ever interpolated into a page.
+func (h *Handler) renderLogin(w http.ResponseWriter, status int, msg string) {
+	h.render(w, status, "login", loginView{Error: msg})
 }

+// logout revokes the session row and clears the cookie in one step: the next
+// request finds no row and is rejected.
 func (h *Handler) logout(w http.ResponseWriter, r *http.Request) {
+	if c, err := r.Cookie(session.CookieName); err == nil {
+		if err := h.store.DeleteSession(c.Value); err != nil {
+			log.Printf("delete session: %v", err)
+		}
+	}
 	session.ClearCookie(w, r)
 	http.Redirect(w, r, "/", http.StatusSeeOther)
 }
@@ -378,7 +391,7 @@ func (h *Handler) loadForMutation(w http.ResponseWriter, r *http.Request) (store
 		http.Error(w, "missing key", http.StatusBadRequest)
 		return store.Bookmark{}, false
 	}
-	b, ok, err := h.store.Get(h.readerID, key)
+	b, ok, err := h.store.Get(readerOf(r), key)
 	if err != nil {
 		log.Printf("ui get %q: %v", key, err)
 		http.Error(w, "internal error", http.StatusInternalServerError)
@@ -401,7 +414,7 @@ func (h *Handler) loadForMutation(w http.ResponseWriter, r *http.Request) (store
 // describe the whole library, so they are rebuilt out of band on every
 // mutation, at the cost of one extra list read per toggle.
 func (h *Handler) saveAndRenderCard(w http.ResponseWriter, r *http.Request, b store.Bookmark) {
-	stored, err := h.store.Upsert(h.readerID, b)
+	stored, err := h.store.Upsert(readerOf(r), b)
 	if err != nil {
 		log.Printf("ui upsert %q: %v", b.Key, err)
 		http.Error(w, "internal error", http.StatusInternalServerError)
@@ -493,7 +506,7 @@ func (h *Handler) uiDelete(w http.ResponseWriter, r *http.Request) {
 		http.Error(w, "missing key", http.StatusBadRequest)
 		return
 	}
-	if err := h.store.Delete(h.readerID, key); err != nil {
+	if err := h.store.Delete(readerOf(r), key); err != nil {
 		log.Printf("ui delete %q: %v", key, err)
 		http.Error(w, "internal error", http.StatusInternalServerError)
 		return