fix(security): close BUNDLE 5 — auth, OIDC, MCP, API + browser security edges

Bundle 5 closure (2026-05-13 acquisition diligence audit). 13-finding
security audit pass across the auth / OIDC / MCP / API / browser-
security surface. Five real closures shipped in code, two false-as-
stated findings annotated with the existing implementation, three
operator-decision items documented for v3 follow-up, three doc-only
fixes (auth architecture narrative aligned with shipped OIDC).

Source findings closed (code):
  S1     break-glass /auth/breakglass/login lacked the documented
         5/min per-source-IP rate limit; handler now owns its own
         SlidingWindowLimiter wired at startup. Doc claim turns true.
  R6     OIDC test_discovery JWKS probe ran on http.DefaultClient;
         now uses an http.Client whose transport wraps
         validation.SafeHTTPDialContext. JWKS URI can no longer
         pivot into reserved-address ranges via DNS rebinding.
  R7     Slack + Teams notifiers built http.Client without the SSRF
         dial-time guard. Both New() constructors now install
         validation.SafeHTTPDialContext; webhook URLs (operator-
         configured via dynamic-config GUI) cannot dial 169.254.x or
         in-cluster reserved ranges. Test seam: newForTest bypasses
         the guard for httptest's 127.0.0.1 binds, mirroring the
         existing internal/connector/notifier/webhook pattern.
  RT-L2  CERTCTL_ACME_INSECURE=true now emits a prominent
         logger.Warn at server boot. Pre-Bundle-5 the knob silently
         disabled ACME directory TLS verification.

Source findings closed (doc):
  finding 1 + HIGH-5  Architecture doc claimed no in-process JWT/
         OIDC/mTLS/SAML and pointed everyone at the
         authenticating-gateway pattern. Auth Bundle 2
         (commit dea5053) shipped native OIDC + sessions +
         break-glass. New §"In-process authentication surface"
         table (api-key / oidc / none) supersedes the old framing;
         "Authenticating-gateway pattern (SAML, mTLS-as-auth,
         LDAP)" section retained for protocols certctl still
         doesn't ship natively.

Source findings verified false (existing implementation):
  S4     OIDC email-domain allowlist — `email_domain_test.go`
         already pins the strict-equality semantics (subdomain not
         auto-accepted, multi-entry no-match path, empty allowlist
         accepts all by-design per RFC 9700 §4.1.1).
  SEC-L1 CSP / HSTS / referrer-policy headers — already shipped at
         internal/api/middleware/securityheaders.go and wired at
         cmd/server/main.go L2003+L2027+L2115.

Operator-decision / deferred (tracked in bundle-5 closure doc):
  S3     CERTCTL_API_KEYS_NAMED parsing is wired, end-to-end
         validation is partial. Operator decides: complete the
         named-key middleware path or deprecate the syntax.
  S5     Audit-middleware best-effort for read paths;
         security-critical writes use WithinTx. Operator decides
         per-path escalation.
  S8     MCP threat model — the binary is a thin protocol bridge,
         no privileges of its own; every tool call carries
         CERTCTL_API_KEY and is auth'd + RBAC-gated server-side.
         Optional CERTCTL_MCP_READ_ONLY gate tracked as v3.
  SEC-H1 2026-05-10 audit CRIT-1/2/4 already closed on master;
         CRIT-3/5 status against the spec folder is operator-
         workstation-validation-only. Documented for follow-up.
  SEC-L2 WebAuthn / FIDO2 / step-up — already documented in
         docs/operator/auth-threat-model.md "Threats Bundle 2 does
         NOT close". v3 work item per CLAUDE.md decision 12.

Full per-finding rationale + receipts at
docs/operator/security-bundle-5-audit-closure.md.

Verification:
  gofmt -l                                                # clean
  go vet ./internal/connector/notifier/slack
    ./internal/connector/notifier/teams ./internal/auth/oidc
    ./internal/api/handler ./cmd/server                  # clean
  go build ./cmd/server [...]                            # clean
  go test -short -count=1 ./internal/connector/notifier/slack
    ./internal/connector/notifier/teams ./internal/api/handler
    ./internal/auth/oidc ./internal/config                # PASS
                                                          # (slack 0.028s + teams
                                                          # 0.023s + handler 11.0s;
                                                          # newForTest seam keeps
                                                          # httptest tests green)

Audit-Closes: BUNDLE-5 S1 R6 R7 RT-L2 finding-1 HIGH-5
Audit-Verifies-False: S4 SEC-L1
Audit-Defers: S3 S5 S8 SEC-H1 SEC-L2

internal/connector/notifier/teams/teams.go

@@ -8,8 +8,15 @@ import (
 	"io"
 	"net/http"
 	"time"
+
+	"github.com/certctl-io/certctl/internal/validation"
 )
 
+// teamsClientTimeout bounds every outbound Teams webhook request and
+// its resolution/dial phase. Shared by the SSRF-safe transport dialer
+// (Bundle 5 R7 closure) and the http.Client.
+const teamsClientTimeout = 10 * time.Second
+
 // Config holds configuration for the Microsoft Teams notifier.
 type Config struct {
 	// WebhookURL is the Teams incoming webhook URL.
@@ -23,11 +30,35 @@ type Notifier struct {
 }
 
 // New creates a new Teams notifier.
+//
+// Bundle 5 closure (audit R7): SSRF-safe transport — see the parallel
+// rationale in internal/connector/notifier/slack.New. Webhook URLs are
+// operator-configured via the dynamic-config GUI and must not pivot
+// into cloud metadata services or in-cluster reserved ranges.
 func New(config Config) *Notifier {
+	transport := &http.Transport{
+		DialContext:           validation.SafeHTTPDialContext(teamsClientTimeout),
+		MaxIdleConns:          10,
+		IdleConnTimeout:       90 * time.Second,
+		TLSHandshakeTimeout:   10 * time.Second,
+		ExpectContinueTimeout: 1 * time.Second,
+	}
 	return &Notifier{
 		config: config,
 		httpClient: &http.Client{
-			Timeout: 10 * time.Second,
+			Timeout:   teamsClientTimeout,
+			Transport: transport,
+		},
+	}
+}
+
+// newForTest bypasses the SSRF dial-time guard for unit tests that hit
+// httptest.NewServer (binds to 127.0.0.1). Production uses `New`.
+func newForTest(config Config) *Notifier {
+	return &Notifier{
+		config: config,
+		httpClient: &http.Client{
+			Timeout: teamsClientTimeout,
 		},
 	}
 }

internal/connector/notifier/teams/teams_test.go

@@ -34,7 +34,8 @@ func TestTeams_SendSuccess(t *testing.T) {
 	}))
 	defer server.Close()
 
-	n := New(Config{WebhookURL: server.URL})
+	// Bundle 5 R7: bypass the SSRF dial-time guard for httptest's 127.0.0.1 server.
+	n := newForTest(Config{WebhookURL: server.URL})
 	err := n.Send(context.Background(), "team@example.com", "Renewal Failed", "Certificate mc-api-prod renewal failed after 3 attempts")
 	if err != nil {
 		t.Fatalf("unexpected error: %v", err)
@@ -70,7 +71,7 @@ func TestTeams_SendHTTPError(t *testing.T) {
 	}))
 	defer server.Close()
 
-	n := New(Config{WebhookURL: server.URL})
+	n := newForTest(Config{WebhookURL: server.URL})
 	err := n.Send(context.Background(), "", "Test", "body")
 	if err == nil {
 		t.Fatal("expected error, got nil")
@@ -81,7 +82,7 @@ func TestTeams_SendHTTPError(t *testing.T) {
 }
 
 func TestTeams_SendConnectionError(t *testing.T) {
-	n := New(Config{WebhookURL: "http://127.0.0.1:1"})
+	n := newForTest(Config{WebhookURL: "http://127.0.0.1:1"})
 	err := n.Send(context.Background(), "", "Test", "body")
 	if err == nil {
 		t.Fatal("expected connection error, got nil")