Phase 3+4: 共享 HTTP 客户端 + admin API + audit log

Phase 3 (httpclient):
- shared Client (Timeout + MaxResponseBytes 截断)
- SSRF: 16 段私网 CIDR (含 169.254/::ffff:0:0/96 IPv4-mapped)
  + hostname allowlist (精确/后缀/*. 通配)
  + scheme 校验 (仅 http/https)
- auth 适配器: none / simple (YARN user.name) / basic (SetBasicAuth)
- DoWithRedirect: 跨主机跳转保留 Authorization, max 5 默认
- 19 个测试全绿 (httptest 模拟)

Phase 4 (admin + audit):
- internal/audit: Entry + Repo.Insert/List + MarshalDetails, snake_case JSON
- internal/middleware: AdminAuth/AgentAuth (constant-time 比对)
- internal/admin: 6 端点 (GET/POST/PUT/DELETE /admin/clusters, GET /admin/audit)
  + 写操作触发 audit_log (含 before/after diff)
  + AuthPassword 空=保留旧密码
  + 校验: 必填字段 + auth_type 枚举 + rate_limit>=0
- main.go: 挂载 storage.Open + admin.Mount
- L fix: audit.Entry 加 json tag (smoke test 发现大写 key 不规范)

Co-Authored-By: Claude <noreply@anthropic.com>

internal/httpclient/redirect_test.go

@@ -0,0 +1,142 @@
+package httpclient
+
+import (
+	"context"
+	"encoding/base64"
+	"io"
+	"net/http"
+	"net/http/httptest"
+	"strings"
+	"testing"
+	"time"
+)
+
+func TestDoWithRedirect_SameHost(t *testing.T) {
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		switch r.URL.Path {
+		case "/start":
+			w.Header().Set("Location", "/final")
+			w.WriteHeader(http.StatusFound)
+		case "/final":
+			w.WriteHeader(http.StatusOK)
+			w.Write([]byte("ok"))
+		default:
+			w.WriteHeader(http.StatusNotFound)
+		}
+	}))
+	defer srv.Close()
+
+	c := New(Config{Timeout: 5 * time.Second, MaxResponseBytes: 1024})
+	req, err := http.NewRequest(http.MethodGet, srv.URL+"/start", nil)
+	if err != nil {
+		t.Fatalf("new request: %v", err)
+	}
+	resp, err := c.DoWithRedirect(context.Background(), req, 5, "127.0.0.1")
+	if err != nil {
+		t.Fatalf("do with redirect: %v", err)
+	}
+	defer resp.Body.Close()
+
+	if resp.StatusCode != http.StatusOK {
+		t.Fatalf("status=%d, want 200", resp.StatusCode)
+	}
+	body, _ := io.ReadAll(resp.Body)
+	if string(body) != "ok" {
+		t.Fatalf("body=%q, want ok", string(body))
+	}
+}
+
+func TestDoWithRedirect_CrossHost_PreservesAuth(t *testing.T) {
+	srv2 := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(http.StatusOK)
+		w.Write([]byte(r.Header.Get("Authorization")))
+	}))
+	defer srv2.Close()
+
+	srv1 := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if r.URL.Path == "/start" {
+			w.Header().Set("Location", srv2.URL+"/final")
+			w.WriteHeader(http.StatusTemporaryRedirect)
+			return
+		}
+		w.WriteHeader(http.StatusNotFound)
+	}))
+	defer srv1.Close()
+
+	c := New(Config{Timeout: 5 * time.Second, MaxResponseBytes: 1024})
+	req, err := http.NewRequest(http.MethodGet, srv1.URL+"/start", nil)
+	if err != nil {
+		t.Fatalf("new request: %v", err)
+	}
+	req.SetBasicAuth("u", "p")
+
+	resp, err := c.DoWithRedirect(context.Background(), req, 5, "127.0.0.1")
+	if err != nil {
+		t.Fatalf("do with redirect: %v", err)
+	}
+	defer resp.Body.Close()
+
+	body, err := io.ReadAll(resp.Body)
+	if err != nil {
+		t.Fatalf("read body: %v", err)
+	}
+	want := "Basic " + base64.StdEncoding.EncodeToString([]byte("u:p"))
+	if string(body) != want {
+		t.Fatalf("body=%q, want %q", string(body), want)
+	}
+}
+
+func TestDoWithRedirect_MaxLimit(t *testing.T) {
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.Header().Set("Location", "/loop")
+		w.WriteHeader(http.StatusFound)
+	}))
+	defer srv.Close()
+
+	c := New(Config{Timeout: 5 * time.Second, MaxResponseBytes: 1024})
+	req, _ := http.NewRequest(http.MethodGet, srv.URL+"/loop", nil)
+	_, err := c.DoWithRedirect(context.Background(), req, 2, "127.0.0.1")
+	if err == nil {
+		t.Fatal("expected too many redirects error")
+	}
+	if !strings.Contains(err.Error(), "too many redirects") {
+		t.Fatalf("expected too many redirects, got %v", err)
+	}
+}
+
+func TestDoWithRedirect_NoLocation(t *testing.T) {
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(http.StatusFound)
+	}))
+	defer srv.Close()
+
+	c := New(Config{Timeout: 5 * time.Second, MaxResponseBytes: 1024})
+	req, _ := http.NewRequest(http.MethodGet, srv.URL, nil)
+	_, err := c.DoWithRedirect(context.Background(), req, 5, "127.0.0.1")
+	if err == nil {
+		t.Fatal("expected error for missing Location")
+	}
+	if !strings.Contains(err.Error(), "without Location header") {
+		t.Fatalf("expected missing Location error, got %v", err)
+	}
+}
+
+func TestDoWithRedirect_ZeroDisallows(t *testing.T) {
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.Header().Set("Location", "/elsewhere")
+		w.WriteHeader(http.StatusFound)
+	}))
+	defer srv.Close()
+
+	c := New(Config{Timeout: 5 * time.Second, MaxResponseBytes: 1024})
+	req, _ := http.NewRequest(http.MethodGet, srv.URL, nil)
+	resp, err := c.DoWithRedirect(context.Background(), req, 0, "127.0.0.1")
+	if err != nil {
+		t.Fatalf("do: %v", err)
+	}
+	defer resp.Body.Close()
+
+	if resp.StatusCode != http.StatusFound {
+		t.Fatalf("status=%d, want 302", resp.StatusCode)
+	}
+}