secret: migrate EJBCA / GlobalSign / Sectigo credentials to *secret.Ref (Phase 2)

Phase 2 of the #6 acquisition-readiness fix from the 2026-05-01 issuer
coverage audit. Phase 1 (commit 633a10a) shipped the secret.Ref opaque
credential type with PBKDF2-derived key, ChaCha20-Poly1305 envelope,
String/MarshalJSON redaction to "[redacted]", and the Use callback
that zero-fills the per-call buffer after the consumer returns.

This commit applies the type to the three connectors flagged by the
audit and adds the JSON-roundtrip glue that the production factory
path needs.

Shared (internal/secret/):

- Add UnmarshalJSON on *Ref so json.Unmarshal of a stored config
  blob (issuerfactory.NewFromConfig) parses the bytes-as-string into
  NewRefFromString without callers having to know the field type
  changed. Null and missing keys leave the receiver nil; non-string
  payloads (numbers, bools) are rejected with a typed error. Pinned
  by TestRef_UnmarshalJSON: string_value, null, missing_key,
  number_rejected, roundtrip_marshal_then_unmarshal (the round-trip
  goes through "[redacted]" intentionally — JSON-marshal-then-
  unmarshal of a Config with secrets is NOT a supported test pattern;
  callers that construct a rawConfig must use a JSON literal with
  the real values).

Per-connector migration:

- EJBCA (ejbca.go): Config.Token: string → *secret.Ref. ValidateConfig
  empty-check uses Token.IsEmpty() (nil-safe). setAuthHeaders rewritten
  to call Token.Use; the Bearer header string is built inside the
  callback and the buffer is zeroed on return. mTLS path is
  unaffected.

- GlobalSign (globalsign.go): Config.APIKey + Config.APISecret: string
  → *secret.Ref. Both ValidateConfig empty-checks use IsEmpty().
  Extracted setAuthHeaders helper consolidates the four duplicated
  triple-Set sites (ValidateConfig probe, IssueCertificate,
  RevokeCertificate, pollCertificateOnce) so any future header-shape
  change applies once. ValidateConfig now pulls from the local cfg
  (post-Unmarshal) so the helper takes a *Config rather than the
  receiver — needed because ValidateConfig writes the validated cfg
  onto c.config only AFTER the probe succeeds.

- Sectigo (sectigo.go): Config.Login + Config.Password: string →
  *secret.Ref. CustomerURI stays plain string (org identifier, not
  a credential). setAuthHeaders rewritten to call Login.Use +
  Password.Use; ValidateConfig's inline header writes use the same
  pattern (the ValidateConfig probe writes to a local cfg, not
  c.config, so it can't share setAuthHeaders without rewiring — the
  inline form is fine, kept consistent in shape).

Test migration:

- ejbca_test.go, ejbca_failure_test.go, ejbca_stubs_test.go: bulk
  Token: "X" → Token: secret.NewRefFromString("X") via sed; secret
  import added.
- globalsign_test.go, globalsign_failure_test.go: same pattern for
  APIKey + APISecret.
- sectigo_test.go, sectigo_failure_test.go: same pattern for Login +
  Password.

Two tests (TestGlobalSign_ServerTLSConfig/PinnedCA_TrustsExpectedServer
and TestSectigoConnector/ValidateConfig_Success) used to construct
rawConfig via json.Marshal(config) → ValidateConfig(rawConfig). After
the migration, json.Marshal redacts *secret.Ref to "[redacted]" by
design, so the roundtripped rawConfig wrote "[redacted]" as the
actual header value and the mock server's auth-header check 403'd.
Both tests now build rawConfig as a JSON literal (the production-
shape input — the factory path always feeds rawConfig from the DB
or env, never from json.Marshal of an in-memory Config). The new
tests have a comment explaining the trap so the next person who
adds a similar test sees the pattern.

Out of scope (intentional):

- The `internal/config/config.SectigoConfig` / `GlobalSignConfig` /
  `EJBCAConfig` env-var-loader structs are still plain strings —
  those types are the env-load shape, not the steady-state runtime
  shape. The seed path in service/issuer.go json-marshals them into
  a map[string]interface{} which the factory then UnmarshalJSON's
  into the connector Config; the new UnmarshalJSON on *Ref handles
  the conversion at the boundary.
- DigiCert.APIKey + Vault.Token are still plain strings; Phase 3
  will pick them up. The audit explicitly named EJBCA / GlobalSign /
  Sectigo as the Phase 2 scope (RESULTS.md L633).

Verified locally:
- gofmt -l . clean
- go vet ./... clean
- staticcheck across all four packages clean
- go test -short -count=1 across secret, ejbca, globalsign, sectigo,
  issuerfactory, service, api/handler: green

Audit reference: cowork/issuer-coverage-audit-2026-05-01/RESULTS.md
Top-10 fix #6 — Phase 2.

internal/connector/issuer/sectigo/sectigo.go

@@ -38,6 +38,7 @@ import (
 
 	"github.com/shankar0123/certctl/internal/connector/issuer"
 	"github.com/shankar0123/certctl/internal/connector/issuer/asyncpoll"
+	"github.com/shankar0123/certctl/internal/secret"
 )
 
 // Config represents the Sectigo Certificate Manager issuer connector configuration.
@@ -48,11 +49,16 @@ type Config struct {
 
 	// Login is the Sectigo API account login.
 	// Required. Set via CERTCTL_SECTIGO_LOGIN environment variable.
-	Login string `json:"login"`
+	//
+	// Type: *secret.Ref (audit fix #6 Phase 2). Login can be tied to
+	// a privileged service-account identity, so it's protected from
+	// accidental logging the same way Password is.
+	Login *secret.Ref `json:"login"`
 
 	// Password is the Sectigo API account password or API key.
 	// Required. Set via CERTCTL_SECTIGO_PASSWORD environment variable.
-	Password string `json:"password"`
+	// Same *secret.Ref protections as Login.
+	Password *secret.Ref `json:"password"`
 
 	// OrgID is the Sectigo organization ID for certificate enrollments.
 	// Required. Set via CERTCTL_SECTIGO_ORG_ID environment variable.
@@ -144,10 +150,27 @@ type statusResponse struct {
 }
 
 // setAuthHeaders sets the three Sectigo authentication headers on a request.
+//
+// Login and Password are pulled from *secret.Ref via Use, which zero-fills
+// the per-call buffer after the header string is set; the Ref's underlying
+// bytes remain encrypted at rest. The Use return value is intentionally
+// ignored — Set never errors and the only failure modes inside Use are
+// nil-Ref / empty-Ref which the upstream IsEmpty validation has already
+// excluded for production paths. Audit fix #6 Phase 2.
 func (c *Connector) setAuthHeaders(req *http.Request) {
 	req.Header.Set("customerUri", c.config.CustomerURI)
-	req.Header.Set("login", c.config.Login)
-	req.Header.Set("password", c.config.Password)
+	if c.config.Login != nil {
+		_ = c.config.Login.Use(func(buf []byte) error {
+			req.Header.Set("login", string(buf))
+			return nil
+		})
+	}
+	if c.config.Password != nil {
+		_ = c.config.Password.Use(func(buf []byte) error {
+			req.Header.Set("password", string(buf))
+			return nil
+		})
+	}
 	req.Header.Set("Content-Type", "application/json")
 }
 
@@ -162,11 +185,11 @@ func (c *Connector) ValidateConfig(ctx context.Context, rawConfig json.RawMessag
 		return fmt.Errorf("Sectigo customer_uri is required")
 	}
 
-	if cfg.Login == "" {
+	if cfg.Login.IsEmpty() {
 		return fmt.Errorf("Sectigo login is required")
 	}
 
-	if cfg.Password == "" {
+	if cfg.Password.IsEmpty() {
 		return fmt.Errorf("Sectigo password is required")
 	}
 
@@ -188,8 +211,18 @@ func (c *Connector) ValidateConfig(ctx context.Context, rawConfig json.RawMessag
 		return fmt.Errorf("failed to create API test request: %w", err)
 	}
 	req.Header.Set("customerUri", cfg.CustomerURI)
-	req.Header.Set("login", cfg.Login)
-	req.Header.Set("password", cfg.Password)
+	if cfg.Login != nil {
+		_ = cfg.Login.Use(func(buf []byte) error {
+			req.Header.Set("login", string(buf))
+			return nil
+		})
+	}
+	if cfg.Password != nil {
+		_ = cfg.Password.Use(func(buf []byte) error {
+			req.Header.Set("password", string(buf))
+			return nil
+		})
+	}
 	req.Header.Set("Content-Type", "application/json")
 
 	resp, err := c.httpClient.Do(req)