Wire logging: drop auth token-exchange records, elide huge payload fields

The option.WithLogger logger also reaches cloud.google.com/go/auth,
which logged its token exchange at Debug — JWT assertion and bearer
token included. wireLogger now allowlists only the compute client's
api request/response records at Debug (fail-closed for future SDK
additions); Warn/Error pass through. String fields over 1KiB (e.g.
Shielded-VM UEFI dbx blobs) are elided recursively by default; the new
--gcp-wire-log-full-payloads flag restores verbatim payloads.

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

internal/provider/gcp/gcp.go

@@ -9,7 +9,6 @@ package gcp
 import (
 	"context"
 	"fmt"
-	"log/slog"
 	"strings"
 	"time"
 
@@ -85,28 +84,27 @@ type Provider struct {
 	api  instancesAPI
 }
 
-// wireLogger returns the slog logger handed to the SDK: its Debug-level
-// "api request"/"api response" records (slog Debug = +4 on the logr
-// scale) land at V(5) on top of the base's V(1) shift.
-func wireLogger(base logr.Logger) *slog.Logger {
-	return slog.New(logr.ToSlogHandler(base.V(1)))
-}
-
 // New builds a Provider using Application Default Credentials (workload
 // identity in-cluster, gcloud ADC locally — no key-file plumbing).
 // Deliberately untested: it dials real Google endpoints; everything below
 // it is exercised through newWithAPI.
-//
-// The injected wire logger surfaces the SDK's raw HTTP request/response
-// records at V(5); note option.WithLogger overrides the SDK's own
-// GOOGLE_SDK_GO_LOGGING_LEVEL env var, so --zap-log-level is the only knob.
 func New(ctx context.Context, pc provider.ProviderConfig) (provider.Provider, error) {
+	return NewWithWireOptions(ctx, pc, WireLogOptions{})
+}
+
+// NewWithWireOptions is New with explicit control over the V(5) wire
+// logging; the injected wire logger surfaces the SDK's HTTP
+// request/response records at V(5). Note option.WithLogger overrides the
+// SDK's own GOOGLE_SDK_GO_LOGGING_LEVEL env var, so --zap-log-level is
+// the only knob.
+func NewWithWireOptions(ctx context.Context, pc provider.ProviderConfig, opts WireLogOptions) (provider.Provider, error) {
 	base := logf.Log.WithName("gcp").WithName("http")
 	if base.V(5).Enabled() {
 		logf.Log.WithName("gcp").Info(
-			"GCP HTTP wire logging active — request payloads include cloud-init user-data")
+			"GCP HTTP wire logging active — request payloads include cloud-init user-data",
+			"fullPayloads", opts.FullPayloads)
 	}
-	client, err := compute.NewInstancesRESTClient(ctx, option.WithLogger(wireLogger(base)))
+	client, err := compute.NewInstancesRESTClient(ctx, option.WithLogger(wireLogger(base, opts)))
 	if err != nil {
 		return nil, fmt.Errorf("creating GCP instances client: %w", err)
 	}

internal/provider/gcp/gcp_test.go

@@ -3,6 +3,7 @@ package gcp
 import (
 	"context"
 	"errors"
+	"log/slog"
 	"strings"
 	"testing"
 	"time"
@@ -418,7 +419,7 @@ func TestWireLogger_gatesAtV5(t *testing.T) {
 				*lines = append(*lines, prefix+" "+args)
 			}, funcr.Options{Verbosity: tc.verbosity})
 
-			slogger := wireLogger(base)
+			slogger := wireLogger(base, WireLogOptions{})
 			slogger.Debug("api request", "rpcName", "Insert")
 
 			joined := strings.Join(*lines, "\n")
@@ -439,13 +440,84 @@ func TestWireLogger_infoLandsAtV1(t *testing.T) {
 		*lines = append(*lines, prefix+" "+args)
 	}, funcr.Options{Verbosity: 1})
 
-	wireLogger(base).Info("hello")
+	wireLogger(base, WireLogOptions{}).Info("hello")
 
 	if joined := strings.Join(*lines, "\n"); !strings.Contains(joined, "hello") {
 		t.Errorf("slog Info should land at V(1) and be visible at verbosity 1; output:\n%s", joined)
 	}
 }
 
+func captureWireLogger(verbosity int, opts WireLogOptions) (*slog.Logger, *[]string) {
+	lines := &[]string{}
+	base := funcr.New(func(prefix, args string) {
+		*lines = append(*lines, prefix+" "+args)
+	}, funcr.Options{Verbosity: verbosity})
+	return wireLogger(base, opts), lines
+}
+
+func TestWireLogger_dropsNonAPIDebugRecords(t *testing.T) {
+	t.Parallel()
+	slogger, lines := captureWireLogger(9, WireLogOptions{})
+
+	const secret = "assertion=eyJhbGciOiJSUzI1NiJ9.SECRET"
+	slogger.Debug("2LO token request", "request", map[string]any{"payload": secret})
+	slogger.Debug("2LO token response", "response", map[string]any{"payload": "ya29.SECRET-TOKEN"})
+
+	if len(*lines) != 0 {
+		t.Errorf("auth token-exchange records must be dropped; got:\n%s", strings.Join(*lines, "\n"))
+	}
+
+	slogger.Warn("credential refresh failed")
+	if joined := strings.Join(*lines, "\n"); !strings.Contains(joined, "credential refresh failed") {
+		t.Errorf("non-debug SDK records should pass through; output:\n%s", joined)
+	}
+}
+
+func TestWireLogger_elidesLargeFields(t *testing.T) {
+	t.Parallel()
+	slogger, lines := captureWireLogger(9, WireLogOptions{})
+
+	huge := strings.Repeat("x", 4096)
+	slogger.Debug("api response", "response", map[string]any{
+		"status": "200",
+		"payload": map[string]any{
+			"name":  "proxy-abc",
+			"disks": []any{map[string]any{"content": huge}},
+		},
+	})
+
+	joined := strings.Join(*lines, "\n")
+	if strings.Contains(joined, huge[:64]) {
+		t.Errorf("large field not elided:\n%.500s", joined)
+	}
+	if !strings.Contains(joined, "[elided 4096 bytes]") {
+		t.Errorf("elision marker missing:\n%s", joined)
+	}
+	for _, keep := range []string{"proxy-abc", "200", "api response"} {
+		if !strings.Contains(joined, keep) {
+			t.Errorf("small field %q lost during elision:\n%s", keep, joined)
+		}
+	}
+}
+
+func TestWireLogger_fullPayloadsDisablesElision(t *testing.T) {
+	t.Parallel()
+	slogger, lines := captureWireLogger(9, WireLogOptions{FullPayloads: true})
+
+	huge := strings.Repeat("y", 4096)
+	slogger.Debug("api response", "response", map[string]any{"payload": huge})
+
+	joined := strings.Join(*lines, "\n")
+	if !strings.Contains(joined, huge) {
+		t.Errorf("FullPayloads should keep fields verbatim:\n%.200s", joined)
+	}
+
+	slogger.Debug("2LO token response", "response", "ya29.SECRET")
+	if joined := strings.Join(*lines, "\n"); strings.Contains(joined, "ya29.SECRET") {
+		t.Error("auth records must be dropped even with FullPayloads")
+	}
+}
+
 func TestLogging_apiErrorKeepsHTTPDetail(t *testing.T) {
 	t.Parallel()
 	ctx, lines := captureContext(1)

internal/provider/gcp/wirelog.go

@@ -0,0 +1,117 @@
+package gcp
+
+import (
+	"context"
+	"fmt"
+	"log/slog"
+
+	"github.com/go-logr/logr"
+)
+
+// wireLogMaxFieldBytes is the elision threshold for string fields in wire
+// payloads: GCP responses embed multi-KB blobs (Shielded-VM UEFI dbx
+// databases, licenses) that swamp the log line without diagnostic value.
+const wireLogMaxFieldBytes = 1024
+
+// WireLogOptions controls the V(5) HTTP wire logging of the GCP SDK.
+type WireLogOptions struct {
+	// FullPayloads disables field elision and logs payloads verbatim.
+	FullPayloads bool
+}
+
+// wireLogger returns the slog logger handed to the SDK: its Debug-level
+// "api request"/"api response" records (slog Debug = +4 on the logr
+// scale) land at V(5) on top of the base's V(1) shift.
+//
+// Debug records other than the compute client's api request/response are
+// dropped entirely: the same logger propagates into the auth library,
+// whose token-exchange records contain the signed JWT assertion and the
+// bearer access token. Warnings and errors pass through.
+func wireLogger(base logr.Logger, opts WireLogOptions) *slog.Logger {
+	return slog.New(&wireFilterHandler{
+		inner:        logr.ToSlogHandler(base.V(1)),
+		fullPayloads: opts.FullPayloads,
+	})
+}
+
+type wireFilterHandler struct {
+	inner        slog.Handler
+	fullPayloads bool
+}
+
+func (h *wireFilterHandler) Enabled(ctx context.Context, level slog.Level) bool {
+	return h.inner.Enabled(ctx, level)
+}
+
+func (h *wireFilterHandler) Handle(ctx context.Context, rec slog.Record) error {
+	if rec.Level <= slog.LevelDebug && rec.Message != "api request" && rec.Message != "api response" {
+		return nil
+	}
+	if h.fullPayloads {
+		return h.inner.Handle(ctx, rec)
+	}
+	elided := slog.NewRecord(rec.Time, rec.Level, rec.Message, rec.PC)
+	rec.Attrs(func(a slog.Attr) bool {
+		elided.AddAttrs(slog.Attr{Key: a.Key, Value: elideValue(a.Value)})
+		return true
+	})
+	return h.inner.Handle(ctx, elided)
+}
+
+func (h *wireFilterHandler) WithAttrs(attrs []slog.Attr) slog.Handler {
+	return &wireFilterHandler{inner: h.inner.WithAttrs(attrs), fullPayloads: h.fullPayloads}
+}
+
+func (h *wireFilterHandler) WithGroup(name string) slog.Handler {
+	return &wireFilterHandler{inner: h.inner.WithGroup(name), fullPayloads: h.fullPayloads}
+}
+
+func elideValue(v slog.Value) slog.Value {
+	v = v.Resolve()
+	switch v.Kind() {
+	case slog.KindString:
+		if s := v.String(); len(s) > wireLogMaxFieldBytes {
+			return slog.StringValue(elisionMarker(len(s)))
+		}
+		return v
+	case slog.KindGroup:
+		attrs := v.Group()
+		out := make([]slog.Attr, 0, len(attrs))
+		for _, a := range attrs {
+			out = append(out, slog.Attr{Key: a.Key, Value: elideValue(a.Value)})
+		}
+		return slog.GroupValue(out...)
+	case slog.KindAny:
+		return slog.AnyValue(elideAny(v.Any()))
+	default:
+		return v
+	}
+}
+
+func elideAny(v any) any {
+	switch t := v.(type) {
+	case string:
+		if len(t) > wireLogMaxFieldBytes {
+			return elisionMarker(len(t))
+		}
+		return t
+	case map[string]any:
+		out := make(map[string]any, len(t))
+		for k, val := range t {
+			out[k] = elideAny(val)
+		}
+		return out
+	case []any:
+		out := make([]any, len(t))
+		for i, val := range t {
+			out[i] = elideAny(val)
+		}
+		return out
+	default:
+		return v
+	}
+}
+
+func elisionMarker(size int) string {
+	return fmt.Sprintf("[elided %d bytes]", size)
+}