Cache issued tgz in memory for one-time download

Instead of streaming the tgz directly to the response (which was
fragile under server write timeouts), handleIssueCert now:
- Builds the tgz into a bytes.Buffer
- Stores it in a sync.Map (tgzCache) under a random 16-byte hex token
- Redirects the browser to /pki/download/{token}

handleTGZDownload serves the cached bytes via LoadAndDelete, so the
archive is removed from memory after the first (and only) download.
An unknown or already-used token returns 404.

Also adds TestHandleTGZDownload covering the one-time-use and
not-found cases, and wires issueCertFn into mockVault.

Co-authored-by: Junie <junie@jetbrains.com>

internal/webserver/cert_detail_test.go

@@ -24,6 +24,7 @@ type mockVault struct {
 	validateTokenFn func(ctx context.Context, token string) (*TokenInfo, error)
 	listMountsFn    func(ctx context.Context, token string) ([]MountInfo, error)
 	getCertFn       func(ctx context.Context, token, mount, serial string) (*CertDetail, error)
+	issueCertFn     func(ctx context.Context, token string, req IssueCertRequest) (*IssuedCert, error)
 }
 
 func (m *mockVault) Status(ctx context.Context) (string, error) {
@@ -80,6 +81,9 @@ func (m *mockVault) ListIssuers(ctx context.Context, token, mount string) ([]str
 }
 
 func (m *mockVault) IssueCert(ctx context.Context, token string, req IssueCertRequest) (*IssuedCert, error) {
+	if m.issueCertFn != nil {
+		return m.issueCertFn(ctx, token, req)
+	}
 	return nil, fmt.Errorf("not implemented")
 }
 
@@ -108,6 +112,62 @@ func (m *mockVault) DeleteCert(ctx context.Context, token, mount, serial string)
 
 func (m *mockVault) Close() error { return nil }
 
+// ---- handleTGZDownload tests ----
+
+func TestHandleTGZDownload(t *testing.T) {
+	t.Run("valid token serves archive and removes it from cache", func(t *testing.T) {
+		ws := newTestWebServer(t, &mockVault{})
+
+		const dlToken = "abc123"
+		ws.tgzCache.Store(dlToken, &tgzEntry{
+			filename: "test.tgz",
+			data:     []byte("fake-tgz-data"),
+		})
+
+		r := newChiRequest(http.MethodGet, "/pki/download/"+dlToken, map[string]string{"token": dlToken})
+		r = addAuthCookie(r, &TokenInfo{Username: "testuser"})
+
+		w := httptest.NewRecorder()
+		ws.handleTGZDownload(w, r)
+
+		if w.Code != http.StatusOK {
+			t.Errorf("status = %d, want %d", w.Code, http.StatusOK)
+		}
+		if ct := w.Header().Get("Content-Type"); ct != "application/gzip" {
+			t.Errorf("Content-Type = %q, want application/gzip", ct)
+		}
+		if body := w.Body.String(); body != "fake-tgz-data" {
+			t.Errorf("body = %q, want fake-tgz-data", body)
+		}
+
+		// Entry must have been removed — a second request should 404.
+		w2 := httptest.NewRecorder()
+		r2 := newChiRequest(http.MethodGet, "/pki/download/"+dlToken, map[string]string{"token": dlToken})
+		r2 = addAuthCookie(r2, &TokenInfo{Username: "testuser"})
+		ws.handleTGZDownload(w2, r2)
+		if w2.Code != http.StatusNotFound {
+			t.Errorf("second request status = %d, want %d", w2.Code, http.StatusNotFound)
+		}
+	})
+
+	t.Run("unknown token returns 404", func(t *testing.T) {
+		ws := newTestWebServer(t, &mockVault{})
+
+		r := newChiRequest(http.MethodGet, "/pki/download/nosuchtoken", map[string]string{"token": "nosuchtoken"})
+		r = addAuthCookie(r, &TokenInfo{Username: "testuser"})
+
+		w := httptest.NewRecorder()
+		ws.handleTGZDownload(w, r)
+
+		if w.Code != http.StatusNotFound {
+			t.Errorf("status = %d, want %d", w.Code, http.StatusNotFound)
+		}
+		if !strings.Contains(w.Body.String(), "download not found") {
+			t.Errorf("body %q does not contain 'download not found'", w.Body.String())
+		}
+	})
+}
+
 // newTestWebServer builds a WebServer wired to the given mock, suitable for unit tests.
 func newTestWebServer(t *testing.T, vault vaultBackend) *WebServer {
 	t.Helper()

internal/webserver/routes.go

@@ -2,7 +2,10 @@ package webserver
 
 import (
 	"archive/tar"
+	"bytes"
 	"compress/gzip"
+	"crypto/rand"
+	"encoding/hex"
 	"fmt"
 	"io"
 	"net/http"
@@ -40,6 +43,7 @@ func (ws *WebServer) registerRoutes(r chi.Router) {
 		r.Post("/import-root", ws.requireAuth(ws.handleImportRoot))
 		r.Post("/create-issuer", ws.requireAuth(ws.handleCreateIssuer))
 		r.Post("/issue", ws.requireAuth(ws.handleIssueCert))
+		r.Get("/download/{token}", ws.requireAuth(ws.handleTGZDownload))
 		r.Get("/issuer/{issuer}", ws.requireAuth(ws.handleIssuerDetail))
 		r.Get("/cert/{serial}", ws.requireAuth(ws.handleCertDetail))
 		r.Get("/cert/{serial}/download", ws.requireAuth(ws.handleCertDownload))
@@ -479,11 +483,6 @@ func (ws *WebServer) handleIssuerDetail(w http.ResponseWriter, r *http.Request)
 }
 
 func (ws *WebServer) handleIssueCert(w http.ResponseWriter, r *http.Request) {
-	// Disable the server-wide write deadline for this handler: it streams a
-	// tgz response only after several serial gRPC calls, which can easily
-	// consume the 30 s WriteTimeout before we start writing.  We set our own
-	// 60 s deadline just before the write phase below.
-	_ = http.NewResponseController(w).SetWriteDeadline(time.Time{})
 
 	info := tokenInfoFromContext(r.Context())
 	token := extractCookie(r)
@@ -538,17 +537,11 @@ func (ws *WebServer) handleIssueCert(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
-	// Stream a tgz archive containing the private key (PKCS8) and certificate.
-	// Extend the write deadline before streaming so that slow gRPC backends
-	// don't consume the server WriteTimeout before we start writing.
-	rc := http.NewResponseController(w)
-	_ = rc.SetWriteDeadline(time.Now().Add(60 * time.Second))
-
-	filename := issuedCert.Serial + ".tgz"
-	w.Header().Set("Content-Type", "application/gzip")
-	w.Header().Set("Content-Disposition", "attachment; filename=\""+filename+"\"")
-
-	gw := gzip.NewWriter(w)
+	// Build the tgz archive in memory, store it in the cache, then redirect
+	// the browser to the one-time download URL so the archive is only served
+	// once and then discarded.
+	var buf bytes.Buffer
+	gw := gzip.NewWriter(&buf)
 	tw := tar.NewWriter(gw)
 
 	writeTarFile := func(name string, data []byte) error {
@@ -566,16 +559,48 @@ func (ws *WebServer) handleIssueCert(w http.ResponseWriter, r *http.Request) {
 	}
 
 	if err := writeTarFile("key.pem", []byte(issuedCert.KeyPEM)); err != nil {
-		ws.logger.Error("write key to tgz", "error", err)
+		ws.logger.Error("build tgz key", "error", err)
+		http.Error(w, "failed to build archive", http.StatusInternalServerError)
 		return
 	}
 	if err := writeTarFile("cert.pem", []byte(issuedCert.CertPEM)); err != nil {
-		ws.logger.Error("write cert to tgz", "error", err)
+		ws.logger.Error("build tgz cert", "error", err)
+		http.Error(w, "failed to build archive", http.StatusInternalServerError)
 		return
 	}
-
 	_ = tw.Close()
 	_ = gw.Close()
+
+	// Generate a random one-time token for the download URL.
+	var raw [16]byte
+	if _, err := rand.Read(raw[:]); err != nil {
+		ws.logger.Error("generate download token", "error", err)
+		http.Error(w, "internal server error", http.StatusInternalServerError)
+		return
+	}
+	dlToken := hex.EncodeToString(raw[:])
+
+	ws.tgzCache.Store(dlToken, &tgzEntry{
+		filename: issuedCert.Serial + ".tgz",
+		data:     buf.Bytes(),
+	})
+
+	http.Redirect(w, r, "/pki/download/"+dlToken, http.StatusSeeOther)
+}
+
+func (ws *WebServer) handleTGZDownload(w http.ResponseWriter, r *http.Request) {
+	dlToken := chi.URLParam(r, "token")
+
+	val, ok := ws.tgzCache.LoadAndDelete(dlToken)
+	if !ok {
+		http.Error(w, "download not found or already used", http.StatusNotFound)
+		return
+	}
+	entry := val.(*tgzEntry)
+
+	w.Header().Set("Content-Type", "application/gzip")
+	w.Header().Set("Content-Disposition", "attachment; filename=\""+entry.filename+"\"")
+	_, _ = w.Write(entry.data)
 }
 
 func (ws *WebServer) handleCertDetail(w http.ResponseWriter, r *http.Request) {

internal/webserver/server.go

@@ -10,6 +10,7 @@ import (
 	"io/fs"
 	"log/slog"
 	"net/http"
+	"sync"
 	"time"
 
 	"github.com/go-chi/chi/v5"
@@ -42,6 +43,12 @@ type vaultBackend interface {
 	Close() error
 }
 
+// tgzEntry holds a cached tgz archive pending download.
+type tgzEntry struct {
+	filename string
+	data     []byte
+}
+
 // WebServer is the standalone web UI server.
 type WebServer struct {
 	cfg      *config.Config
@@ -49,6 +56,7 @@ type WebServer struct {
 	logger   *slog.Logger
 	httpSrv  *http.Server
 	staticFS fs.FS
+	tgzCache sync.Map // key: UUID string → *tgzEntry
 }
 
 // New creates a new WebServer. It dials the vault gRPC endpoint.