Connect customer quotations and payment execution to Sendico (#50)

backend/product/identity/verification.go

@@ -147,3 +147,13 @@ func (s *Service) SubmitVerification(ctx context.Context, a *customer.Account, k
 	s.Logger.Info("Identity proofs accepted for review", zap.String("account_ref", a.ID.Hex()), zap.String("submission_ref", v.SubmissionID))
 	return v, nil
 }
+
+// Subject resolves the authenticated customer's confirmed provider binding.
+// Only server-side services may use this resource; clients cannot select it.
+func (s *Service) Subject(ctx context.Context, a *customer.Account) (string, error) {
+	b, err := s.binding(ctx, a)
+	if err != nil {
+		return "", err
+	}
+	return b.SubjectRef, nil
+}