cdrop — 跨 OS 剪贴板与文件传输服务

Commilitia Drop：自托管的跨设备剪贴板同步与点对点文件传输。

- 后端 Go（chi / SQLite WAL / SSE Hub / WebRTC signaling + 状态机 / Relay ring buffer），编译进单个 distroless 镜像（前端 go:embed）。
- 前端 React + TanStack Router + Zustand，自实现 SSE + WebRTC P2P，NAT 受阻时回退服务端中继；聚珍（Juzhen）CJK 综合排版。
- 桌面端 Wails v2（macOS / Windows），瘦客户端复用 web。
- 鉴权 OIDC PKCE（自建 Casdoor 等），refresh_token 信封加密存系统密钥库；iOS Shortcut 用 HS256 scoped token。

架构文档与变更记录见 docs 分支（PROJECT_BRIEF / FRONTEND_DESIGN / CHANGELOG）。

本次为公开发布初始提交：完整开发历史（含部署细节）留存于私有归档，公开仓库自此干净起步。

internal/jwtauth/jwks.go

@@ -0,0 +1,113 @@
+package jwtauth
+
+import (
+	"context"
+	"crypto/rsa"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"io"
+	"log/slog"
+	"net/http"
+	"sync"
+	"time"
+
+	"github.com/go-jose/go-jose/v4"
+)
+
+// jwksCache fetches & caches the Casdoor JWKS.
+//
+// Behavior:
+//   - successful fetch: refreshes the entire key set
+//   - kid miss: forces a single refresh attempt
+//   - stale-while-error: if cached entry exists, return it even when refresh fails
+type jwksCache struct {
+	url string
+	ttl time.Duration
+
+	mu        sync.RWMutex
+	keys      map[string]*rsa.PublicKey
+	fetchedAt time.Time
+
+	httpClient *http.Client
+}
+
+func newJWKSCache(url string, ttl time.Duration) *jwksCache {
+	return &jwksCache{
+		url:        url,
+		ttl:        ttl,
+		keys:       map[string]*rsa.PublicKey{},
+		httpClient: &http.Client{Timeout: 5 * time.Second},
+	}
+}
+
+func (j *jwksCache) GetKey(ctx context.Context, kid string) (*rsa.PublicKey, error) {
+	if kid == "" {
+		return nil, errors.New("missing kid")
+	}
+
+	j.mu.RLock()
+	cached, found := j.keys[kid]
+	fresh := !j.fetchedAt.IsZero() && time.Since(j.fetchedAt) < j.ttl
+	j.mu.RUnlock()
+
+	if found && fresh {
+		return cached, nil
+	}
+
+	if err := j.refresh(ctx); err != nil {
+		if found {
+			slog.Warn("jwks refresh failed; returning stale key",
+				"err", err, "kid", kid)
+			return cached, nil
+		}
+		return nil, fmt.Errorf("jwks refresh: %w", err)
+	}
+
+	j.mu.RLock()
+	defer j.mu.RUnlock()
+	if k, ok := j.keys[kid]; ok {
+		return k, nil
+	}
+	return nil, fmt.Errorf("kid %q not found in JWKS", kid)
+}
+
+func (j *jwksCache) refresh(ctx context.Context) error {
+	req, err := http.NewRequestWithContext(ctx, http.MethodGet, j.url, nil)
+	if err != nil {
+		return err
+	}
+	resp, err := j.httpClient.Do(req)
+	if err != nil {
+		return err
+	}
+	defer resp.Body.Close()
+
+	if resp.StatusCode != http.StatusOK {
+		return fmt.Errorf("status %d", resp.StatusCode)
+	}
+	body, err := io.ReadAll(resp.Body)
+	if err != nil {
+		return err
+	}
+
+	var set jose.JSONWebKeySet
+	if err := json.Unmarshal(body, &set); err != nil {
+		return fmt.Errorf("parse JWKS: %w", err)
+	}
+
+	next := map[string]*rsa.PublicKey{}
+	for _, k := range set.Keys {
+		pk, ok := k.Key.(*rsa.PublicKey)
+		if !ok || k.KeyID == "" {
+			continue
+		}
+		next[k.KeyID] = pk
+	}
+
+	j.mu.Lock()
+	defer j.mu.Unlock()
+	j.keys = next
+	j.fetchedAt = time.Now()
+	return nil
+}