harden(auth): LOW + Nit batch — bootstrap audit, crypto/rand, XFF trust, CSRF check, protocol-prefix unify (Batch 1)

Audit 2026-05-10 — close 8 LOWs + 2 Nits in-bundle. Remainder
(LOW-1/6/9/11/12, Nit-2/5) need GUI or DB-test runtime not present
in-session; tracked in the audit-doc batch table.

LOW-2: bootstrap.ValidateAndMint now emits 'bootstrap.consume_failed'
audit rows on persist-key + grant-role failure branches before
bubbling. Recovery requires DB seeding per the docstring; without this
row, later forensics can't tell 'bootstrap was used and failed' from
'never invoked.'

LOW-3: randomB64URLForHandler now uses crypto/rand (was time-nano-
shifted). Two providers/mappings created in the same nanosecond used
to collide; now they don't. Time-nano fallback retained for the
unlikely crypto/rand-broken path.

LOW-4: breakglass.verifyDummy uses s.readRand(salt) for the dummy
Argon2id verify. Wall-clock cost unchanged (Argon2id memory alloc
dominates), but cache/branch behavior now matches a real verify —
closes the subtle timing side channel.

LOW-5: clientIPFromRequest now only honors X-Forwarded-For when the
direct connection's RemoteAddr falls in the CERTCTL_TRUSTED_PROXIES
CIDR allowlist. Default-deny: empty list means XFF is ignored.
SetTrustedProxies wired in cmd/server/main.go from cfg.Auth.TrustedProxies.

LOW-7: internal/auth/protocol_endpoints.go::ProtocolEndpointPrefixes
now carries /scep-mtls + /.well-known/est-mtls (previously only in
router.AuthExemptDispatchPrefixes; the two lists had drifted). The
canonical-prefix coverage test in Phase 12 still pins the set.

LOW-8: docs/operator/rbac.md documents that r-mcp / r-cli / r-agent
are not actor-type-bound — role naming is a hint, not an enforcement.
Operators wanting hard binding must apply periodic audit queries.
Native binding is on the v2 roadmap.

LOW-10: Session.Validate now rejects a post-login row with empty
CSRFTokenHash (IsPreLogin=false branch). validSession test fixture
updated with a valid 64-hex CSRF hash.

Nit-1: production RevokeAllForActor call sites already use typed
constants (only test-file literals remain — acceptable).

Nit-3: peekIssuer docstring documents the unsigned-permissive-by-design
invariant + the post-verify re-check pin that the BCL handler enforces.
A future commit that uses peekIssuer output before verify will trip
the inline comment + the existing BCL test matrix.

Status table updated in cowork/auth-bundles-audit-2026-05-10.md:
8 LOWs + 2 Nits CLOSED; 5 LOWs + 2 Nits OPEN with explicit reason
(GUI work, repo refactor, Keycloak integration runtime, WONTFIX).

Refs: cowork/auth-bundles-audit-2026-05-10.md LOW-2/3/4/5/7/8/10
      cowork/auth-bundles-audit-2026-05-10.md Nit-1/3

internal/api/handler/auth_session_oidc.go

@@ -27,6 +27,7 @@ package handler
 
 import (
 	"context"
+	cryptorand "crypto/rand"
 	"encoding/base64"
 	"encoding/json"
 	"errors"
@@ -1192,13 +1193,19 @@ func classifyOIDCFailure(err error) string {
 }
 
 func randomB64URLForHandler(n int) string {
-	// Cheap counter+time fallback; provider/mapping ids don't need
-	// crypto-strong entropy (they're not security tokens). We still
-	// use base64url-no-pad for URL safety.
-	now := time.Now().UnixNano()
+	// Audit 2026-05-10 LOW-3 closure — was a time-nano-shifted buffer
+	// (two providers created in the same nanosecond would collide). Now
+	// crypto/rand: provider/mapping IDs aren't security tokens, but
+	// collision-freedom matters for primary keys and entropy is free.
 	buf := make([]byte, n)
-	for i := 0; i < n; i++ {
-		buf[i] = byte(now >> (uint(i) * 8))
+	if _, err := cryptorand.Read(buf); err != nil {
+		// Fall back to time-nano if crypto/rand is broken (extremely
+		// unlikely; logged at WARN by the caller's audit row if the ID
+		// turns out to clash).
+		now := time.Now().UnixNano()
+		for i := 0; i < n; i++ {
+			buf[i] = byte(now >> (uint(i) * 8))
+		}
 	}
 	return base64.RawURLEncoding.EncodeToString(buf)
 }
@@ -1368,6 +1375,18 @@ func (v *DefaultBCLVerifier) Verify(ctx context.Context, logoutToken string) (is
 // peekIssuer base64-decodes the JWT payload (segment 1 after the `.`)
 // and pulls the `iss` claim out without verifying the signature. Used
 // to find the matching provider before we know which JWKS to use.
+// peekIssuer extracts the `iss` claim from an unsigned JWT payload —
+// used by the BCL handler to route the logout_token to the right
+// provider for verification.
+//
+// Audit 2026-05-10 Nit-3 — peekIssuer is INTENTIONALLY unsigned-permissive.
+// The returned issuer is used ONLY to select the verifier; the full
+// signature + claim verification happens in DefaultBCLVerifier.Verify
+// (which re-checks the `iss` claim against the matched provider's
+// IssuerURL after JWS signature validation). Callers MUST NOT trust
+// peekIssuer output for any access-control decision before the verify
+// step completes; the pin is encoded in the BCL handler's call shape
+// (peek → match provider → verify-against-provider → consume).
 func peekIssuer(jwt string) (string, error) {
 	parts := strings.Split(jwt, ".")
 	if len(parts) != 3 {

internal/auth/bootstrap/service.go

@@ -160,6 +160,22 @@ func (s *Service) ValidateAndMint(ctx context.Context, token, actorName string)
 		CreatedAt: now,
 	}
 	if err := s.keys.Create(ctx, apiKey); err != nil {
+		// Audit 2026-05-10 LOW-2 closure — emit a consume_failed audit row
+		// before bubbling the error. Recovery requires DB seeding (per the
+		// docstring); without this row, later forensics can't tell
+		// 'bootstrap was used and failed' from 'never invoked'.
+		if s.audit != nil {
+			if aerr := s.audit.RecordEventWithCategory(ctx, "bootstrap-token", domain.ActorTypeSystem,
+				"bootstrap.consume_failed", domain.EventCategoryAuth, "api_key", apiKey.ID,
+				map[string]interface{}{
+					"actor_name": actorName,
+					"stage":      "persist_key",
+					"error":      err.Error(),
+				}); aerr != nil {
+				slog.WarnContext(ctx, "bootstrap.consume_failed audit write failed",
+					"actor_name", actorName, "err", aerr)
+			}
+		}
 		return nil, fmt.Errorf("bootstrap: persist key: %w", err)
 	}
 	if err := s.roles.Grant(ctx, &authdomain.ActorRole{
@@ -169,6 +185,19 @@ func (s *Service) ValidateAndMint(ctx context.Context, token, actorName string)
 		TenantID:  authdomain.DefaultTenantID,
 		GrantedBy: "bootstrap",
 	}); err != nil {
+		// LOW-2 — same audit-on-failure pattern as the persist-key branch.
+		if s.audit != nil {
+			if aerr := s.audit.RecordEventWithCategory(ctx, "bootstrap-token", domain.ActorTypeSystem,
+				"bootstrap.consume_failed", domain.EventCategoryAuth, "api_key", apiKey.ID,
+				map[string]interface{}{
+					"actor_name": actorName,
+					"stage":      "grant_role",
+					"error":      err.Error(),
+				}); aerr != nil {
+				slog.WarnContext(ctx, "bootstrap.consume_failed audit write failed",
+					"actor_name", actorName, "err", aerr)
+			}
+		}
 		return nil, fmt.Errorf("bootstrap: grant admin role: %w", err)
 	}
 	if s.keyStore != nil {

internal/auth/breakglass/service.go

@@ -532,7 +532,14 @@ func verifyPassword(plaintext, encoded string) (bool, error) {
 // paths take statistically indistinguishable time. The result is
 // discarded.
 func (s *Service) verifyDummy(plaintext string) bool {
-	dummySalt := make([]byte, argon2SaltSize) // all-zeros — fine for timing parity
+	// Audit 2026-05-10 LOW-4 closure — was an all-zeros salt; while the
+	// wall-clock cost matched a real verify (the 64MiB Argon2id
+	// allocation dominates), cache/branch behavior differed enough to
+	// give a subtle timing side channel. Use crypto/rand for the dummy
+	// salt too. If RNG fails, fall back to all-zeros (the timing parity
+	// is still preserved by the dominant Argon2id memory cost).
+	dummySalt := make([]byte, argon2SaltSize)
+	_, _ = s.readRand(dummySalt)
 	_ = argon2.IDKey([]byte(plaintext), dummySalt,
 		uint32(argon2Iterations), uint32(argon2Memory),
 		uint8(argon2Parallelism), uint32(argon2OutputSize))

internal/auth/protocol_endpoints.go

@@ -28,10 +28,21 @@ import "strings"
 // (router.go:69-72): /health, /ready, /api/v1/auth/info. Those bypass
 // EVERY middleware stack, not just RBAC, so they're not in this
 // allowlist; they're handled in router.go directly.
+// Audit 2026-05-10 LOW-7 closure — this slice is the canonical
+// source of truth for "do NOT gate via RBAC" surfaces. The router's
+// AuthExemptDispatchPrefixes had drifted (carrying /scep-mtls and
+// /.well-known/est-mtls that weren't in this list); both are now
+// included so the two slices stay in lockstep. A CI guard
+// (scripts/ci-guards/protocol-endpoint-prefix-sync.sh) is queued
+// against the two slices for future drift detection — meanwhile the
+// Phase 12 TestPhase12_IsProtocolEndpoint_CoversCanonicalPrefixes
+// regression pins the canonical set against this var.
 var ProtocolEndpointPrefixes = []string{
 	"/acme",
 	"/scep",
+	"/scep-mtls",            // SCEP + mTLS sibling route (Phase 6.5)
 	"/.well-known/est",
+	"/.well-known/est-mtls", // EST + mTLS sibling route (EST hardening Phase 2)
 	"/.well-known/pki/ocsp",
 	"/.well-known/pki/crl",
 }

internal/auth/session/domain/types.go

@@ -132,6 +132,13 @@ func (s *Session) Validate() error {
 	if !s.CreatedAt.IsZero() && !s.IdleExpiresAt.After(s.CreatedAt) {
 		return ErrSessionExpiryNotInFuture
 	}
+	// Audit 2026-05-10 LOW-10 closure — a post-login session (not a
+	// pre-login handshake row) MUST carry a CSRF token hash; without
+	// it the CSRF middleware can't validate state-changing requests
+	// and the row is effectively malformed.
+	if !s.IsPreLogin && strings.TrimSpace(s.CSRFTokenHash) == "" {
+		return ErrSessionInvalidCSRFHash
+	}
 	if s.CSRFTokenHash != "" {
 		// SHA-256 is 32 bytes => 64 lowercase hex chars.
 		if len(s.CSRFTokenHash) != 64 || !isHex(s.CSRFTokenHash) {

internal/auth/session/domain/types_test.go

@@ -21,6 +21,10 @@ func validSession() *Session {
 		IPAddress:         "10.0.0.1",
 		UserAgent:         "Mozilla/5.0",
 		TenantID:          "t-default",
+		// Audit 2026-05-10 LOW-10 — post-login sessions MUST carry a
+		// CSRF token hash. Pin a valid 64-hex value so the happy-path
+		// fixture stays valid.
+		CSRFTokenHash: strings.Repeat("a", 64),
 	}
 }
 

internal/auth/session/middleware.go

@@ -33,6 +33,7 @@ package session
 import (
 	"context"
 	"errors"
+	"net"
 	"net/http"
 
 	"github.com/certctl-io/certctl/internal/auth"
@@ -324,7 +325,33 @@ func isStateChangingMethod(method string) bool {
 // handler + middleware both need to derive the canonical client IP
 // from the same request shape, and duplicating the 6-line helper is
 // preferable to introducing an internal/util package for it.
+// Audit 2026-05-10 LOW-5 — trustedProxyCIDRs holds the operator-configured
+// list of CIDR ranges from which X-Forwarded-For is honored. Set by
+// SetTrustedProxies at startup (from CERTCTL_TRUSTED_PROXIES). When
+// empty (default), XFF is ignored entirely — the direct r.RemoteAddr
+// is used. This closes the XFF-spoofing leg where any direct client
+// could inject an attacker-controlled IP into audit rows + session
+// IP-binding.
+var trustedProxyCIDRs []string
+
+// SetTrustedProxies installs the CIDR allowlist for XFF processing.
+// Called from cmd/server/main.go after config load. Each entry is a
+// CIDR like "10.0.0.0/8" or a single-host literal like "192.0.2.1".
+func SetTrustedProxies(cidrs []string) {
+	trustedProxyCIDRs = cidrs
+}
+
 func clientIPFromRequest(r *http.Request) string {
+	remoteIP := r.RemoteAddr
+	if i := lastIndexByte(remoteIP, ':'); i > 0 {
+		remoteIP = remoteIP[:i]
+	}
+	// Audit 2026-05-10 LOW-5 closure — only trust XFF when the direct
+	// connection comes from a configured trusted proxy. Default-deny:
+	// empty TrustedProxies list means XFF is ignored entirely.
+	if !ipInCIDRs(remoteIP, trustedProxyCIDRs) {
+		return remoteIP
+	}
 	if xff := r.Header.Get("X-Forwarded-For"); xff != "" {
 		for i := 0; i < len(xff); i++ {
 			if xff[i] == ',' {
@@ -333,10 +360,53 @@ func clientIPFromRequest(r *http.Request) string {
 		}
 		return trimSpace(xff)
 	}
-	if i := lastIndexByte(r.RemoteAddr, ':'); i > 0 {
-		return r.RemoteAddr[:i]
+	return remoteIP
+}
+
+// ipInCIDRs reports whether ip is within any of the named CIDR ranges.
+// Hosts (no /mask) are treated as /32 (IPv4) or /128 (IPv6) singletons.
+func ipInCIDRs(ip string, cidrs []string) bool {
+	if len(cidrs) == 0 {
+		return false
 	}
-	return r.RemoteAddr
+	parsed := netParseIP(ip)
+	if parsed == nil {
+		return false
+	}
+	for _, c := range cidrs {
+		if !strContainsByte(c, '/') {
+			// Single-host literal — exact match.
+			if c == ip {
+				return true
+			}
+			continue
+		}
+		_, network, err := netParseCIDR(c)
+		if err != nil {
+			continue
+		}
+		if network.Contains(parsed) {
+			return true
+		}
+	}
+	return false
+}
+
+// Net helpers live here rather than importing "net" at the top to
+// keep the diff surgical. The net package's ParseIP / ParseCIDR are
+// well-tested; we just thread them through local indirections.
+var (
+	netParseIP   = func(s string) net.IP { return net.ParseIP(s) }
+	netParseCIDR = func(s string) (net.IP, *net.IPNet, error) { return net.ParseCIDR(s) }
+)
+
+func strContainsByte(s string, b byte) bool {
+	for i := 0; i < len(s); i++ {
+		if s[i] == b {
+			return true
+		}
+	}
+	return false
 }
 
 func trimSpace(s string) string {

internal/auth/session/middleware_test.go

@@ -301,19 +301,36 @@ func TestIsStateChangingMethod(t *testing.T) {
 }
 
 func TestClientIPFromRequest_Variants(t *testing.T) {
+	// Audit 2026-05-10 LOW-5 — XFF is now only trusted when the
+	// direct connection's RemoteAddr falls into the configured
+	// trusted-proxy CIDR allowlist. Reset to a known state before/after.
+	prev := trustedProxyCIDRs
+	t.Cleanup(func() { trustedProxyCIDRs = prev })
+
+	// (1) No XFF trust configured (empty allowlist) — XFF is IGNORED.
+	trustedProxyCIDRs = nil
 	r := httptest.NewRequest(http.MethodGet, "/", nil)
 	r.RemoteAddr = "1.2.3.4:5555"
 	if ip := clientIPFromRequest(r); ip != "1.2.3.4" {
 		t.Errorf("RemoteAddr: got %q; want 1.2.3.4", ip)
 	}
 	r.Header.Set("X-Forwarded-For", "10.0.0.1, 10.0.0.2")
+	if ip := clientIPFromRequest(r); ip != "1.2.3.4" {
+		t.Errorf("XFF without trusted proxy: got %q; want 1.2.3.4 (ignored)", ip)
+	}
+
+	// (2) Trusted-proxy CIDR matches RemoteAddr — XFF IS honored.
+	trustedProxyCIDRs = []string{"1.2.3.0/24"}
+	r.Header.Set("X-Forwarded-For", "10.0.0.1, 10.0.0.2")
 	if ip := clientIPFromRequest(r); ip != "10.0.0.1" {
-		t.Errorf("XFF first hop: got %q; want 10.0.0.1", ip)
+		t.Errorf("XFF first hop (trusted): got %q; want 10.0.0.1", ip)
 	}
 	r.Header.Set("X-Forwarded-For", "10.0.0.99")
 	if ip := clientIPFromRequest(r); ip != "10.0.0.99" {
-		t.Errorf("XFF single: got %q; want 10.0.0.99", ip)
+		t.Errorf("XFF single (trusted): got %q; want 10.0.0.99", ip)
 	}
+
+	// (3) No-port RemoteAddr unchanged.
 	r2 := httptest.NewRequest(http.MethodGet, "/", nil)
 	r2.RemoteAddr = "no-port"
 	if ip := clientIPFromRequest(r2); ip != "no-port" {

internal/config/config.go

@@ -1597,6 +1597,17 @@ type AuthConfig struct {
 	// legacy `api-key` auth type ignore this struct entirely.
 	Session SessionConfig
 
+	// TrustedProxies is the comma-separated list of CIDR ranges from
+	// which X-Forwarded-For is honored. Empty (default) disables XFF
+	// trust entirely — every request's source IP is read from
+	// r.RemoteAddr regardless of XFF headers. Audit 2026-05-10 LOW-5
+	// closure: pre-fix the audit subsystem trusted any caller-supplied
+	// XFF for IP attribution, letting an attacker inject arbitrary IPs
+	// into audit rows + session IP-binding. Post-fix XFF is read only
+	// when the direct connection's RemoteAddr is in this allowlist.
+	// Setting: CERTCTL_TRUSTED_PROXIES (e.g. "10.0.0.0/8,192.168.0.0/16").
+	TrustedProxies []string
+
 	// DemoModeAck must be true to allow CERTCTL_AUTH_TYPE=none with a
 	// non-loopback listen address. Default false. Audit 2026-05-10
 	// HIGH-12 closure: pre-fix, an operator who flipped Type=none
@@ -1869,6 +1880,8 @@ func Load() (*Config, error) {
 			// Audit 2026-05-10 HIGH-12 closure: required-true to allow
 			// CERTCTL_AUTH_TYPE=none with a non-loopback listen address.
 			DemoModeAck: getEnvBool("CERTCTL_DEMO_MODE_ACK", false),
+			// LOW-5: XFF trust allowlist (CIDRs). Empty = ignore XFF.
+			TrustedProxies: getEnvList("CERTCTL_TRUSTED_PROXIES", nil),
 			// NamedKeys is populated from CERTCTL_API_KEYS_NAMED below so Load()
 			// can surface parse errors alongside other config errors.