feat: add RFC 8628 device authorization flow for out-of-VPN authentication

src/cmd/login.go

@@ -22,67 +22,112 @@ var loginCmd = &cobra.Command{
 		}
 		base := fmt.Sprintf("http://%s:%d", rc.Host, rc.Port)
 
-		resp, err := http.Post(base+"/auth/start", "application/json", nil)
+		sessionID := tryDeviceFlow(base)
+		if sessionID == "" {
+			sessionID = tryCallbackFlow(base)
+		}
+
+		pollForToken(base, sessionID)
+	},
+}
+
+// tryDeviceFlow attempts the device authorization flow. Returns a session ID
+// on success, or "" if the server does not support it.
+func tryDeviceFlow(base string) string {
+	resp, err := http.Post(base+"/auth/device/start", "application/json", nil)
+	if err != nil {
+		return ""
+	}
+	defer resp.Body.Close()
+	if resp.StatusCode != http.StatusOK {
+		return ""
+	}
+	var start struct {
+		SessionID               string `json:"session_id"`
+		UserCode                string `json:"user_code"`
+		VerificationURI         string `json:"verification_uri"`
+		VerificationURIComplete string `json:"verification_uri_complete"`
+	}
+	json.NewDecoder(resp.Body).Decode(&start)
+	if start.SessionID == "" {
+		return ""
+	}
+
+	uri := start.VerificationURI
+	if start.VerificationURIComplete != "" {
+		uri = start.VerificationURIComplete
+	}
+	fmt.Printf("To sign in, open this URL in any browser:\n\n  %s\n\nThen enter this code: %s\n\nWaiting for authentication...\n", uri, start.UserCode)
+	return start.SessionID
+}
+
+// tryCallbackFlow initiates the traditional callback-based OIDC flow.
+// Exits the process on failure.
+func tryCallbackFlow(base string) string {
+	resp, err := http.Post(base+"/auth/start", "application/json", nil)
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "failed to contact server: %v\n", err)
+		os.Exit(1)
+	}
+	var start struct {
+		URL       string `json:"url"`
+		SessionID string `json:"session_id"`
+	}
+	json.NewDecoder(resp.Body).Decode(&start)
+	resp.Body.Close()
+
+	if start.URL == "" {
+		fmt.Fprintln(os.Stderr, "server did not return an auth URL; is OIDC configured on the server?")
+		os.Exit(1)
+	}
+
+	fmt.Printf("Open this URL in your browser:\n\n  %s\n\nWaiting for login...\n", start.URL)
+	return start.SessionID
+}
+
+// pollForToken polls the server until the login completes or times out.
+func pollForToken(base, sessionID string) {
+	deadline := time.Now().Add(5 * time.Minute)
+	for time.Now().Before(deadline) {
+		time.Sleep(2 * time.Second)
+
+		resp, err := http.Get(fmt.Sprintf("%s/auth/poll?session_id=%s", base, sessionID))
 		if err != nil {
-			fmt.Fprintf(os.Stderr, "failed to contact server: %v\n", err)
+			continue
+		}
+		if resp.StatusCode == http.StatusAccepted {
+			resp.Body.Close()
+			continue
+		}
+		if resp.StatusCode != http.StatusOK {
+			resp.Body.Close()
+			fmt.Fprintln(os.Stderr, "login failed")
 			os.Exit(1)
 		}
-		var start struct {
-			URL       string `json:"url"`
-			SessionID string `json:"session_id"`
+
+		var result struct {
+			Token    string `json:"token"`
+			Username string `json:"username"`
 		}
-		json.NewDecoder(resp.Body).Decode(&start)
+		json.NewDecoder(resp.Body).Decode(&result)
 		resp.Body.Close()
 
-		if start.URL == "" {
-			fmt.Fprintln(os.Stderr, "server did not return an auth URL; is OIDC configured on the server?")
+		session, err := store.LoadSession()
+		if err != nil {
+			fmt.Fprintf(os.Stderr, "failed to save session: %v\n", err)
 			os.Exit(1)
 		}
-
-		fmt.Printf("Open this URL in your browser:\n\n  %s\n\nWaiting for login...\n", start.URL)
-
-		deadline := time.Now().Add(5 * time.Minute)
-		for time.Now().Before(deadline) {
-			time.Sleep(2 * time.Second)
-
-			resp, err := http.Get(fmt.Sprintf("%s/auth/poll?session_id=%s", base, start.SessionID))
-			if err != nil {
-				continue
-			}
-			if resp.StatusCode == http.StatusAccepted {
-				resp.Body.Close()
-				continue
-			}
-			if resp.StatusCode != http.StatusOK {
-				resp.Body.Close()
-				fmt.Fprintln(os.Stderr, "login failed")
-				os.Exit(1)
-			}
-
-			var result struct {
-				Token    string `json:"token"`
-				Username string `json:"username"`
-			}
-			json.NewDecoder(resp.Body).Decode(&result)
-			resp.Body.Close()
-
-			session, err := store.LoadSession()
-			if err != nil {
-				fmt.Fprintf(os.Stderr, "failed to save session: %v\n", err)
-				os.Exit(1)
-			}
-			session.Token = result.Token
-			if err := session.Save(); err != nil {
-				fmt.Fprintf(os.Stderr, "failed to save session: %v\n", err)
-				os.Exit(1)
-			}
-			fmt.Printf("Logged in as %s\n", result.Username)
-			return
+		session.Token = result.Token
+		if err := session.Save(); err != nil {
+			fmt.Fprintf(os.Stderr, "failed to save session: %v\n", err)
+			os.Exit(1)
 		}
+		fmt.Printf("Logged in as %s\n", result.Username)
+		return
+	}
 
-		fmt.Fprintln(os.Stderr, "login timed out")
-		os.Exit(1)
-	},
+	fmt.Fprintln(os.Stderr, "login timed out")
+	os.Exit(1)
 }
 
 func init() {

src/serve/auth.go

@@ -23,16 +23,26 @@ type pendingLogin struct {
 	serverToken string // set by callback when complete; empty while pending
 }
 
+// pendingDeviceLogin tracks an in-progress device authorization flow.
+type pendingDeviceLogin struct {
+	created     time.Time
+	serverToken string // set when device token exchange completes
+	username    string // set when device token exchange completes
+	err         string // set if the flow fails
+}
+
 // authHandler owns the OIDC provider connection, the pending login store,
 // and the active server-side session map.
 type authHandler struct {
-	mu       sync.Mutex
-	pending  map[string]*pendingLogin // loginID → pending state
-	sessions map[string]string        // serverToken → username
+	mu            sync.Mutex
+	pending       map[string]*pendingLogin       // loginID → pending state
+	pendingDevice map[string]*pendingDeviceLogin // loginID → pending device state
+	sessions      map[string]string              // serverToken → username
 
-	cfg      store.OIDCConfig
-	provider *oidc.Provider
-	oauth2   oauth2.Config
+	cfg                 store.OIDCConfig
+	provider            *oidc.Provider
+	oauth2              oauth2.Config
+	deviceFlowAvailable bool
 }
 
 func newAuthHandler(cfg store.OIDCConfig) (*authHandler, error) {
@@ -43,18 +53,21 @@ func newAuthHandler(cfg store.OIDCConfig) (*authHandler, error) {
 	if err != nil {
 		return nil, fmt.Errorf("OIDC provider: %w", err)
 	}
+	endpoint := provider.Endpoint()
 	h := &authHandler{
-		pending:  make(map[string]*pendingLogin),
-		sessions: make(map[string]string),
-		cfg:      cfg,
-		provider: provider,
+		pending:       make(map[string]*pendingLogin),
+		pendingDevice: make(map[string]*pendingDeviceLogin),
+		sessions:      make(map[string]string),
+		cfg:           cfg,
+		provider:      provider,
 		oauth2: oauth2.Config{
 			ClientID:     cfg.ClientID,
 			ClientSecret: cfg.ClientSecret,
-			Endpoint:     provider.Endpoint(),
+			Endpoint:     endpoint,
 			RedirectURL:  cfg.PublicURL + "/auth/callback",
 			Scopes:       []string{oidc.ScopeOpenID, "profile", "email", "offline_access"},
 		},
+		deviceFlowAvailable: endpoint.DeviceAuthURL != "",
 	}
 	go h.cleanup()
 	return h, nil
@@ -68,6 +81,11 @@ func (h *authHandler) cleanup() {
 				delete(h.pending, id)
 			}
 		}
+		for id, p := range h.pendingDevice {
+			if time.Since(p.created) > 15*time.Minute {
+				delete(h.pendingDevice, id)
+			}
+		}
 		h.mu.Unlock()
 	}
 }
@@ -148,6 +166,69 @@ func (h *authHandler) callback(w http.ResponseWriter, r *http.Request) {
 	fmt.Fprintln(w, "Login successful! You can close this tab.")
 }
 
+// POST /auth/device/start → {session_id, user_code, verification_uri, verification_uri_complete}
+func (h *authHandler) deviceStart(w http.ResponseWriter, r *http.Request) {
+	if !h.deviceFlowAvailable {
+		writeError(w, http.StatusNotFound, "device flow not supported by OIDC provider")
+		return
+	}
+
+	da, err := h.oauth2.DeviceAuth(r.Context())
+	if err != nil {
+		writeError(w, http.StatusBadGateway, "device authorization request failed: "+err.Error())
+		return
+	}
+
+	loginID := randomToken(16)
+
+	h.mu.Lock()
+	h.pendingDevice[loginID] = &pendingDeviceLogin{created: time.Now()}
+	h.mu.Unlock()
+
+	// Exchange device code for token in the background.
+	go func() {
+		ctx, cancel := context.WithTimeout(context.Background(), 15*time.Minute)
+		defer cancel()
+
+		token, err := h.oauth2.DeviceAccessToken(ctx, da)
+		if err != nil {
+			h.mu.Lock()
+			if p := h.pendingDevice[loginID]; p != nil {
+				p.err = err.Error()
+			}
+			h.mu.Unlock()
+			return
+		}
+
+		username, err := h.extractUsername(ctx, token)
+		if err != nil {
+			h.mu.Lock()
+			if p := h.pendingDevice[loginID]; p != nil {
+				p.err = "failed to identify user: " + err.Error()
+			}
+			h.mu.Unlock()
+			return
+		}
+
+		serverToken := randomToken(32)
+
+		h.mu.Lock()
+		h.sessions[serverToken] = username
+		if p := h.pendingDevice[loginID]; p != nil {
+			p.serverToken = serverToken
+			p.username = username
+		}
+		h.mu.Unlock()
+	}()
+
+	writeJSON(w, map[string]string{
+		"session_id":                loginID,
+		"user_code":                 da.UserCode,
+		"verification_uri":          da.VerificationURI,
+		"verification_uri_complete": da.VerificationURIComplete,
+	})
+}
+
 // GET /auth/poll?session_id=...
 // Returns 202 while pending, 200 {token, username} when done, 404 if expired.
 func (h *authHandler) poll(w http.ResponseWriter, r *http.Request) {
@@ -157,25 +238,52 @@ func (h *authHandler) poll(w http.ResponseWriter, r *http.Request) {
 	p := h.pending[loginID]
 	h.mu.Unlock()
 
-	if p == nil {
+	// Check callback-based flow first.
+	if p != nil {
+		h.mu.Lock()
+		serverToken := p.serverToken
+		if serverToken != "" {
+			delete(h.pending, loginID)
+		}
+		h.mu.Unlock()
+
+		if serverToken == "" {
+			w.WriteHeader(http.StatusAccepted)
+			return
+		}
+		username := h.lookupSession(serverToken)
+		writeJSON(w, map[string]string{"token": serverToken, "username": username})
+		return
+	}
+
+	// Check device flow.
+	h.mu.Lock()
+	dp := h.pendingDevice[loginID]
+	h.mu.Unlock()
+
+	if dp == nil {
 		writeError(w, http.StatusNotFound, "session not found or expired")
 		return
 	}
 
 	h.mu.Lock()
-	serverToken := p.serverToken
-	if serverToken != "" {
-		delete(h.pending, loginID) // consume once delivered
+	serverToken := dp.serverToken
+	errMsg := dp.err
+	if serverToken != "" || errMsg != "" {
+		delete(h.pendingDevice, loginID)
 	}
 	h.mu.Unlock()
 
+	if errMsg != "" {
+		writeError(w, http.StatusGone, errMsg)
+		return
+	}
 	if serverToken == "" {
 		w.WriteHeader(http.StatusAccepted)
 		return
 	}
 
-	username := h.lookupSession(serverToken)
-	writeJSON(w, map[string]string{"token": serverToken, "username": username})
+	writeJSON(w, map[string]string{"token": serverToken, "username": dp.username})
 }
 
 func (h *authHandler) extractUsername(ctx context.Context, token *oauth2.Token) (string, error) {

src/serve/server.go

@@ -30,6 +30,7 @@ func New(newSvc func(user string) (service.NodeService, error), oidcCfg *store.O
 			return nil, err
 		}
 		mux.HandleFunc("POST /auth/start", ah.start)
+		mux.HandleFunc("POST /auth/device/start", ah.deviceStart)
 		mux.HandleFunc("GET /auth/callback", ah.callback)
 		mux.HandleFunc("GET /auth/poll", ah.poll)
 		return withSessionAuth(ah, mux), nil