Add policy-based authz and token delegation

- Replace requireAdmin (role-based) guards on all REST endpoints
  with RequirePolicy middleware backed by the existing policy engine;
  built-in admin wildcard rule (-1) preserves existing admin behaviour
  while operator rules can now grant targeted access to non-admin
  accounts (e.g. a system account allowed to list accounts)
- Wire policy engine into Server: loaded from DB at startup,
  reloaded after every policy-rule create/update/delete so changes
  take effect immediately without a server restart
- Add service_account_delegates table (migration 000008) so a human
  account can be delegated permission to issue tokens for a specific
  system account without holding the admin role
- Add token-download nonce mechanism: a short-lived (5 min),
  single-use random nonce is stored server-side after token issuance;
  the browser downloads the token as a file via
  GET /token/download/{nonce} (Content-Disposition: attachment)
  instead of copying from a flash message
- Add /service-accounts UI page for non-admin delegates
- Add TestPolicyEnforcement and TestPolicyDenyRule integration tests

Security:
- Policy engine uses deny-wins, default-deny semantics; admin wildcard
  is a compiled-in built-in and cannot be deleted via the API
- Token download nonces are 128-bit crypto/rand values, single-use,
  and expire after 5 minutes; a background goroutine evicts stale entries
- alg header validation and Ed25519 signing unchanged

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

internal/server/handlers_policy.go

@@ -217,6 +217,9 @@ func (s *Server) handleCreatePolicyRule(w http.ResponseWriter, r *http.Request)
 	s.writeAudit(r, model.EventPolicyRuleCreated, createdBy, nil,
 		fmt.Sprintf(`{"rule_id":%d,"description":%q}`, rec.ID, rec.Description))
 
+	// Reload the in-memory engine so the new rule takes effect immediately.
+	s.reloadPolicyEngine()
+
 	rv, err := policyRuleToResponse(rec)
 	if err != nil {
 		middleware.WriteError(w, http.StatusInternalServerError, "internal error", "internal_error")
@@ -325,6 +328,9 @@ func (s *Server) handleUpdatePolicyRule(w http.ResponseWriter, r *http.Request)
 	s.writeAudit(r, model.EventPolicyRuleUpdated, actorID, nil,
 		fmt.Sprintf(`{"rule_id":%d}`, rec.ID))
 
+	// Reload the in-memory engine so rule changes take effect immediately.
+	s.reloadPolicyEngine()
+
 	updated, err := s.db.GetPolicyRule(rec.ID)
 	if err != nil {
 		middleware.WriteError(w, http.StatusInternalServerError, "internal error", "internal_error")
@@ -358,6 +364,9 @@ func (s *Server) handleDeletePolicyRule(w http.ResponseWriter, r *http.Request)
 	s.writeAudit(r, model.EventPolicyRuleDeleted, actorID, nil,
 		fmt.Sprintf(`{"rule_id":%d,"description":%q}`, rec.ID, rec.Description))
 
+	// Reload the in-memory engine so the deleted rule is removed immediately.
+	s.reloadPolicyEngine()
+
 	w.WriteHeader(http.StatusNoContent)
 }
 

internal/server/server.go

@@ -13,6 +13,7 @@ import (
 	"encoding/json"
 	"errors"
 	"fmt"
+	"io"
 	"io/fs"
 	"log/slog"
 	"net"
@@ -27,6 +28,7 @@ import (
 	"git.wntrmute.dev/kyle/mcias/internal/db"
 	"git.wntrmute.dev/kyle/mcias/internal/middleware"
 	"git.wntrmute.dev/kyle/mcias/internal/model"
+	"git.wntrmute.dev/kyle/mcias/internal/policy"
 	"git.wntrmute.dev/kyle/mcias/internal/token"
 	"git.wntrmute.dev/kyle/mcias/internal/ui"
 	"git.wntrmute.dev/kyle/mcias/internal/validate"
@@ -40,15 +42,154 @@ type Server struct {
 	cfg    *config.Config
 	logger *slog.Logger
 	vault  *vault.Vault
+	polEng *policy.Engine
 }
 
 // New creates a Server with the given dependencies.
+// The policy engine is initialised and loaded from the database on construction.
 func New(database *db.DB, cfg *config.Config, v *vault.Vault, logger *slog.Logger) *Server {
+	eng := policy.NewEngine()
+	if err := loadEngineRules(eng, database); err != nil {
+		logger.Warn("policy engine initial load failed; built-in defaults will apply", "error", err)
+	}
 	return &Server{
 		db:     database,
 		cfg:    cfg,
 		vault:  v,
 		logger: logger,
+		polEng: eng,
+	}
+}
+
+// loadEngineRules reads all policy rules from the database and loads them into eng.
+// Enabled/disabled and validity-window filtering is handled by the engine itself.
+func loadEngineRules(eng *policy.Engine, database *db.DB) error {
+	records, err := database.ListPolicyRules(false)
+	if err != nil {
+		return fmt.Errorf("list policy rules: %w", err)
+	}
+	prs := make([]policy.PolicyRecord, len(records))
+	for i, r := range records {
+		prs[i] = policy.PolicyRecord{
+			ID:          r.ID,
+			Priority:    r.Priority,
+			Description: r.Description,
+			RuleJSON:    r.RuleJSON,
+			Enabled:     r.Enabled,
+			NotBefore:   r.NotBefore,
+			ExpiresAt:   r.ExpiresAt,
+		}
+	}
+	return eng.SetRules(prs)
+}
+
+// reloadPolicyEngine reloads operator rules from the database into the engine.
+// Called after any create, update, or delete of a policy rule so that the
+// in-memory cache stays consistent with the database.
+func (s *Server) reloadPolicyEngine() {
+	if err := loadEngineRules(s.polEng, s.db); err != nil {
+		s.logger.Error("reload policy engine", "error", err)
+	}
+}
+
+// accountTypeLookup returns an AccountTypeLookup closure that resolves the
+// account type ("human" or "system") for the given subject UUID.  Used by the
+// RequirePolicy middleware to populate PolicyInput.AccountType.
+func (s *Server) accountTypeLookup() middleware.AccountTypeLookup {
+	return func(subjectUUID string) string {
+		acct, err := s.db.GetAccountByUUID(subjectUUID)
+		if err != nil {
+			return ""
+		}
+		return string(acct.AccountType)
+	}
+}
+
+// policyDenyLogger returns a PolicyDenyLogger that records policy denials in
+// the audit log as EventPolicyDeny events.
+func (s *Server) policyDenyLogger() middleware.PolicyDenyLogger {
+	return func(r *http.Request, claims *token.Claims, action policy.Action, res policy.Resource, matchedRuleID int64) {
+		s.writeAudit(r, model.EventPolicyDeny, nil, nil,
+			fmt.Sprintf(`{"subject":%q,"action":%q,"resource_type":%q,"rule_id":%d}`,
+				claims.Subject, action, res.Type, matchedRuleID))
+	}
+}
+
+// buildAccountResource assembles the policy.Resource for endpoints that
+// target a specific account ({id} path parameter).  Looks up the account's
+// UUID, username (for ServiceName), and tags from the database.
+// Returns an empty Resource on lookup failure; deny-by-default in the engine
+// means this safely falls through to a denial for owner-scoped rules.
+func (s *Server) buildAccountResource(r *http.Request, _ *token.Claims) policy.Resource {
+	id := r.PathValue("id")
+	if id == "" {
+		return policy.Resource{}
+	}
+	acct, err := s.db.GetAccountByUUID(id)
+	if err != nil {
+		return policy.Resource{}
+	}
+	tags, _ := s.db.GetAccountTags(acct.ID)
+	return policy.Resource{
+		OwnerUUID:   acct.UUID,
+		ServiceName: acct.Username,
+		Tags:        tags,
+	}
+}
+
+// buildTokenResource assembles the policy.Resource for token-issue requests.
+// The request body contains account_id (UUID); the resource owner is that account.
+// Because this builder reads the body it must be called before the body is
+// consumed by the handler — the middleware calls it before invoking next.
+func (s *Server) buildTokenResource(r *http.Request, _ *token.Claims) policy.Resource {
+	// Peek at the account_id without consuming the body.
+	// We read the body into a small wrapper struct to get the target UUID.
+	// The actual handler re-reads the body via decodeJSON, so this is safe
+	// because http.MaxBytesReader is applied by the handler, not here.
+	var peek struct {
+		AccountID string `json:"account_id"`
+	}
+	body, err := io.ReadAll(io.LimitReader(r.Body, maxJSONBytes))
+	if err != nil {
+		return policy.Resource{}
+	}
+	// Restore the body for the downstream handler.
+	r.Body = io.NopCloser(strings.NewReader(string(body)))
+	if err := json.Unmarshal(body, &peek); err != nil || peek.AccountID == "" {
+		return policy.Resource{}
+	}
+	acct, err := s.db.GetAccountByUUID(peek.AccountID)
+	if err != nil {
+		return policy.Resource{}
+	}
+	tags, _ := s.db.GetAccountTags(acct.ID)
+	return policy.Resource{
+		OwnerUUID:   acct.UUID,
+		ServiceName: acct.Username,
+		Tags:        tags,
+	}
+}
+
+// buildJTIResource assembles the policy.Resource for token-revoke requests.
+// Looks up the token record by {jti} to identify the owning account.
+func (s *Server) buildJTIResource(r *http.Request, _ *token.Claims) policy.Resource {
+	jti := r.PathValue("jti")
+	if jti == "" {
+		return policy.Resource{}
+	}
+	rec, err := s.db.GetTokenRecord(jti)
+	if err != nil {
+		return policy.Resource{}
+	}
+	acct, err := s.db.GetAccountByID(rec.AccountID)
+	if err != nil {
+		return policy.Resource{}
+	}
+	tags, _ := s.db.GetAccountTags(acct.ID)
+	return policy.Resource{
+		OwnerUUID:   acct.UUID,
+		ServiceName: acct.Username,
+		Tags:        tags,
 	}
 }
 
@@ -114,44 +255,92 @@ func (s *Server) Handler() http.Handler {
 
 	// Authenticated endpoints.
 	requireAuth := middleware.RequireAuth(s.vault, s.db, s.cfg.Tokens.Issuer)
-	requireAdmin := func(h http.Handler) http.Handler {
-		return requireAuth(middleware.RequireRole("admin")(h))
+
+	// Policy middleware factory: chains requireAuth → RequirePolicy → next.
+	// All protected endpoints use this instead of the old requireAdmin wrapper
+	// so that operator-defined policy rules (not just the admin role) control
+	// access.  The built-in admin wildcard rule (ID -1) preserves existing
+	// admin behaviour; additional operator rules can grant non-admin accounts
+	// access to specific actions.
+	//
+	// Security: deny-wins + default-deny in the engine mean that any
+	// misconfiguration results in 403, never silent permit.
+	acctTypeLookup := s.accountTypeLookup()
+	denyLogger := s.policyDenyLogger()
+	requirePolicy := func(
+		action policy.Action,
+		resType policy.ResourceType,
+		builder middleware.ResourceBuilder,
+	) func(http.Handler) http.Handler {
+		pol := middleware.RequirePolicy(s.polEng, action, resType, builder, acctTypeLookup, denyLogger)
+		return func(next http.Handler) http.Handler {
+			return requireAuth(pol(next))
+		}
 	}
 
-	// Auth endpoints (require valid token).
+	// Resource builders for endpoints that target a specific account or token.
+	buildAcct := middleware.ResourceBuilder(s.buildAccountResource)
+	buildToken := middleware.ResourceBuilder(s.buildTokenResource)
+	buildJTI := middleware.ResourceBuilder(s.buildJTIResource)
+
+	// Auth endpoints (require valid token; self-service rules in built-in defaults
+	// allow any authenticated principal to perform these operations).
 	mux.Handle("POST /v1/auth/logout", requireAuth(http.HandlerFunc(s.handleLogout)))
 	mux.Handle("POST /v1/auth/renew", requireAuth(http.HandlerFunc(s.handleRenew)))
 	mux.Handle("POST /v1/auth/totp/enroll", requireAuth(http.HandlerFunc(s.handleTOTPEnroll)))
 	mux.Handle("POST /v1/auth/totp/confirm", requireAuth(http.HandlerFunc(s.handleTOTPConfirm)))
 
-	// Admin-only endpoints.
-	mux.Handle("DELETE /v1/auth/totp", requireAdmin(http.HandlerFunc(s.handleTOTPRemove)))
-	mux.Handle("POST /v1/token/issue", requireAdmin(http.HandlerFunc(s.handleTokenIssue)))
-	mux.Handle("DELETE /v1/token/{jti}", requireAdmin(http.HandlerFunc(s.handleTokenRevoke)))
-	mux.Handle("GET /v1/accounts", requireAdmin(http.HandlerFunc(s.handleListAccounts)))
-	mux.Handle("POST /v1/accounts", requireAdmin(http.HandlerFunc(s.handleCreateAccount)))
-	mux.Handle("GET /v1/accounts/{id}", requireAdmin(http.HandlerFunc(s.handleGetAccount)))
-	mux.Handle("PATCH /v1/accounts/{id}", requireAdmin(http.HandlerFunc(s.handleUpdateAccount)))
-	mux.Handle("DELETE /v1/accounts/{id}", requireAdmin(http.HandlerFunc(s.handleDeleteAccount)))
-	mux.Handle("GET /v1/accounts/{id}/roles", requireAdmin(http.HandlerFunc(s.handleGetRoles)))
-	mux.Handle("PUT /v1/accounts/{id}/roles", requireAdmin(http.HandlerFunc(s.handleSetRoles)))
-	mux.Handle("POST /v1/accounts/{id}/roles", requireAdmin(http.HandlerFunc(s.handleGrantRole)))
-	mux.Handle("DELETE /v1/accounts/{id}/roles/{role}", requireAdmin(http.HandlerFunc(s.handleRevokeRole)))
+	// Policy-gated endpoints (formerly admin-only; now controlled by the engine).
+	mux.Handle("DELETE /v1/auth/totp",
+		requirePolicy(policy.ActionRemoveTOTP, policy.ResourceTOTP, buildAcct)(http.HandlerFunc(s.handleTOTPRemove)))
+	mux.Handle("POST /v1/token/issue",
+		requirePolicy(policy.ActionIssueToken, policy.ResourceToken, buildToken)(http.HandlerFunc(s.handleTokenIssue)))
+	mux.Handle("DELETE /v1/token/{jti}",
+		requirePolicy(policy.ActionRevokeToken, policy.ResourceToken, buildJTI)(http.HandlerFunc(s.handleTokenRevoke)))
+	mux.Handle("GET /v1/accounts",
+		requirePolicy(policy.ActionListAccounts, policy.ResourceAccount, nil)(http.HandlerFunc(s.handleListAccounts)))
+	mux.Handle("POST /v1/accounts",
+		requirePolicy(policy.ActionCreateAccount, policy.ResourceAccount, nil)(http.HandlerFunc(s.handleCreateAccount)))
+	mux.Handle("GET /v1/accounts/{id}",
+		requirePolicy(policy.ActionReadAccount, policy.ResourceAccount, buildAcct)(http.HandlerFunc(s.handleGetAccount)))
+	mux.Handle("PATCH /v1/accounts/{id}",
+		requirePolicy(policy.ActionUpdateAccount, policy.ResourceAccount, buildAcct)(http.HandlerFunc(s.handleUpdateAccount)))
+	mux.Handle("DELETE /v1/accounts/{id}",
+		requirePolicy(policy.ActionDeleteAccount, policy.ResourceAccount, buildAcct)(http.HandlerFunc(s.handleDeleteAccount)))
+	mux.Handle("GET /v1/accounts/{id}/roles",
+		requirePolicy(policy.ActionReadRoles, policy.ResourceAccount, buildAcct)(http.HandlerFunc(s.handleGetRoles)))
+	mux.Handle("PUT /v1/accounts/{id}/roles",
+		requirePolicy(policy.ActionWriteRoles, policy.ResourceAccount, buildAcct)(http.HandlerFunc(s.handleSetRoles)))
+	mux.Handle("POST /v1/accounts/{id}/roles",
+		requirePolicy(policy.ActionWriteRoles, policy.ResourceAccount, buildAcct)(http.HandlerFunc(s.handleGrantRole)))
+	mux.Handle("DELETE /v1/accounts/{id}/roles/{role}",
+		requirePolicy(policy.ActionWriteRoles, policy.ResourceAccount, buildAcct)(http.HandlerFunc(s.handleRevokeRole)))
 	mux.Handle("GET /v1/pgcreds", requireAuth(http.HandlerFunc(s.handleListAccessiblePGCreds)))
-	mux.Handle("GET /v1/accounts/{id}/pgcreds", requireAdmin(http.HandlerFunc(s.handleGetPGCreds)))
-	mux.Handle("PUT /v1/accounts/{id}/pgcreds", requireAdmin(http.HandlerFunc(s.handleSetPGCreds)))
-	mux.Handle("GET /v1/audit", requireAdmin(http.HandlerFunc(s.handleListAudit)))
-	mux.Handle("GET /v1/accounts/{id}/tags", requireAdmin(http.HandlerFunc(s.handleGetTags)))
-	mux.Handle("PUT /v1/accounts/{id}/tags", requireAdmin(http.HandlerFunc(s.handleSetTags)))
-	mux.Handle("PUT /v1/accounts/{id}/password", requireAdmin(http.HandlerFunc(s.handleAdminSetPassword)))
+	mux.Handle("GET /v1/accounts/{id}/pgcreds",
+		requirePolicy(policy.ActionReadPGCreds, policy.ResourcePGCreds, buildAcct)(http.HandlerFunc(s.handleGetPGCreds)))
+	mux.Handle("PUT /v1/accounts/{id}/pgcreds",
+		requirePolicy(policy.ActionWritePGCreds, policy.ResourcePGCreds, buildAcct)(http.HandlerFunc(s.handleSetPGCreds)))
+	mux.Handle("GET /v1/audit",
+		requirePolicy(policy.ActionReadAudit, policy.ResourceAuditLog, nil)(http.HandlerFunc(s.handleListAudit)))
+	mux.Handle("GET /v1/accounts/{id}/tags",
+		requirePolicy(policy.ActionReadTags, policy.ResourceAccount, buildAcct)(http.HandlerFunc(s.handleGetTags)))
+	mux.Handle("PUT /v1/accounts/{id}/tags",
+		requirePolicy(policy.ActionWriteTags, policy.ResourceAccount, buildAcct)(http.HandlerFunc(s.handleSetTags)))
+	mux.Handle("PUT /v1/accounts/{id}/password",
+		requirePolicy(policy.ActionUpdateAccount, policy.ResourceAccount, buildAcct)(http.HandlerFunc(s.handleAdminSetPassword)))
 
 	// Self-service password change (requires valid token; actor must match target account).
 	mux.Handle("PUT /v1/auth/password", requireAuth(http.HandlerFunc(s.handleChangePassword)))
-	mux.Handle("GET /v1/policy/rules", requireAdmin(http.HandlerFunc(s.handleListPolicyRules)))
-	mux.Handle("POST /v1/policy/rules", requireAdmin(http.HandlerFunc(s.handleCreatePolicyRule)))
-	mux.Handle("GET /v1/policy/rules/{id}", requireAdmin(http.HandlerFunc(s.handleGetPolicyRule)))
-	mux.Handle("PATCH /v1/policy/rules/{id}", requireAdmin(http.HandlerFunc(s.handleUpdatePolicyRule)))
-	mux.Handle("DELETE /v1/policy/rules/{id}", requireAdmin(http.HandlerFunc(s.handleDeletePolicyRule)))
+	mux.Handle("GET /v1/policy/rules",
+		requirePolicy(policy.ActionListRules, policy.ResourcePolicy, nil)(http.HandlerFunc(s.handleListPolicyRules)))
+	mux.Handle("POST /v1/policy/rules",
+		requirePolicy(policy.ActionManageRules, policy.ResourcePolicy, nil)(http.HandlerFunc(s.handleCreatePolicyRule)))
+	mux.Handle("GET /v1/policy/rules/{id}",
+		requirePolicy(policy.ActionListRules, policy.ResourcePolicy, nil)(http.HandlerFunc(s.handleGetPolicyRule)))
+	mux.Handle("PATCH /v1/policy/rules/{id}",
+		requirePolicy(policy.ActionManageRules, policy.ResourcePolicy, nil)(http.HandlerFunc(s.handleUpdatePolicyRule)))
+	mux.Handle("DELETE /v1/policy/rules/{id}",
+		requirePolicy(policy.ActionManageRules, policy.ResourcePolicy, nil)(http.HandlerFunc(s.handleDeletePolicyRule)))
 
 	// UI routes (HTMX-based management frontend).
 	uiSrv, err := ui.New(s.db, s.cfg, s.vault, s.logger)
@@ -1320,13 +1509,13 @@ func (s *Server) handleListAccessiblePGCreds(w http.ResponseWriter, r *http.Requ
 	type pgCredResponse struct {
 		CreatedAt          time.Time `json:"created_at"`
 		UpdatedAt          time.Time `json:"updated_at"`
-		ID                 int64     `json:"id"`
-		Port               int       `json:"port"`
 		Host               string    `json:"host"`
 		Database           string    `json:"database"`
 		Username           string    `json:"username"`
 		ServiceAccountID   string    `json:"service_account_id"`
 		ServiceAccountName string    `json:"service_account_name,omitempty"`
+		ID                 int64     `json:"id"`
+		Port               int       `json:"port"`
 	}
 
 	response := make([]pgCredResponse, len(creds))

internal/server/server_test.go

@@ -2,10 +2,10 @@ package server
 
 import (
 	"bytes"
-	"crypto/hmac"
-	"crypto/sha1"
 	"crypto/ed25519"
+	"crypto/hmac"
 	"crypto/rand"
+	"crypto/sha1" //nolint:gosec // G505: SHA1 required by RFC 6238 TOTP (HMAC-SHA1)
 	"encoding/binary"
 	"encoding/json"
 	"fmt"
@@ -23,6 +23,7 @@ import (
 	"git.wntrmute.dev/kyle/mcias/internal/config"
 	"git.wntrmute.dev/kyle/mcias/internal/db"
 	"git.wntrmute.dev/kyle/mcias/internal/model"
+	"git.wntrmute.dev/kyle/mcias/internal/policy"
 	"git.wntrmute.dev/kyle/mcias/internal/token"
 	"git.wntrmute.dev/kyle/mcias/internal/vault"
 )
@@ -972,3 +973,149 @@ func TestTOTPMissingDoesNotIncrementLockout(t *testing.T) {
 		t.Error("account was locked after TOTP-missing login — lockout counter was incorrectly incremented (PEN-06)")
 	}
 }
+
+// issueSystemToken creates a system account, issues a JWT with the given roles,
+// tracks it in the database, and returns the token string and account.
+func issueSystemToken(t *testing.T, srv *Server, priv ed25519.PrivateKey, username string, roles []string) (string, *model.Account) {
+	t.Helper()
+	acct, err := srv.db.CreateAccount(username, model.AccountTypeSystem, "")
+	if err != nil {
+		t.Fatalf("create system account: %v", err)
+	}
+	tokenStr, claims, err := token.IssueToken(priv, testIssuer, acct.UUID, roles, time.Hour)
+	if err != nil {
+		t.Fatalf("issue token: %v", err)
+	}
+	if err := srv.db.TrackToken(claims.JTI, acct.ID, claims.IssuedAt, claims.ExpiresAt); err != nil {
+		t.Fatalf("track token: %v", err)
+	}
+	return tokenStr, acct
+}
+
+// TestPolicyEnforcement verifies that the policy engine gates access:
+//   - Admin role is always allowed (built-in wildcard rule).
+//   - Unauthenticated requests are rejected.
+//   - Non-admin accounts are denied by default.
+//   - A non-admin account gains access once an operator policy rule is created.
+//   - Deleting the rule reverts to denial.
+func TestPolicyEnforcement(t *testing.T) {
+	srv, _, priv, _ := newTestServer(t)
+	handler := srv.Handler()
+
+	adminToken, _ := issueAdminToken(t, srv, priv, "admin-pol")
+
+	// 1. Admin can list accounts (built-in wildcard rule -1).
+	rr := doRequest(t, handler, "GET", "/v1/accounts", nil, adminToken)
+	if rr.Code != http.StatusOK {
+		t.Errorf("admin list accounts status = %d, want 200; body: %s", rr.Code, rr.Body.String())
+	}
+
+	// 2. Unauthenticated request is rejected.
+	rr = doRequest(t, handler, "GET", "/v1/accounts", nil, "")
+	if rr.Code != http.StatusUnauthorized {
+		t.Errorf("unauth list accounts status = %d, want 401", rr.Code)
+	}
+
+	// 3. System account with no operator rules is denied by default.
+	svcToken, svcAcct := issueSystemToken(t, srv, priv, "metacrypt", []string{"user"})
+	rr = doRequest(t, handler, "GET", "/v1/accounts", nil, svcToken)
+	if rr.Code != http.StatusForbidden {
+		t.Errorf("system account (no policy) list accounts status = %d, want 403; body: %s", rr.Code, rr.Body.String())
+	}
+
+	// 4. Create an operator policy rule granting the system account accounts:list.
+	rule := createPolicyRuleRequest{
+		Description: "allow metacrypt to list accounts",
+		Priority:    50,
+		Rule: policy.RuleBody{
+			SubjectUUID:  svcAcct.UUID,
+			AccountTypes: []string{"system"},
+			Actions:      []policy.Action{policy.ActionListAccounts},
+			Effect:       policy.Allow,
+		},
+	}
+	rr = doRequest(t, handler, "POST", "/v1/policy/rules", rule, adminToken)
+	if rr.Code != http.StatusCreated {
+		t.Fatalf("create policy rule status = %d, want 201; body: %s", rr.Code, rr.Body.String())
+	}
+	var created policyRuleResponse
+	if err := json.Unmarshal(rr.Body.Bytes(), &created); err != nil {
+		t.Fatalf("unmarshal created rule: %v", err)
+	}
+
+	// 5. The same system account can now list accounts.
+	rr = doRequest(t, handler, "GET", "/v1/accounts", nil, svcToken)
+	if rr.Code != http.StatusOK {
+		t.Errorf("system account (with policy) list accounts status = %d, want 200; body: %s", rr.Code, rr.Body.String())
+	}
+
+	// 6. The system account is still denied other actions (accounts:read).
+	rr = doRequest(t, handler, "POST", "/v1/accounts", map[string]string{
+		"username": "newuser", "password": "newpassword123", "account_type": "human",
+	}, svcToken)
+	if rr.Code != http.StatusForbidden {
+		t.Errorf("system account (list-only policy) create account status = %d, want 403", rr.Code)
+	}
+
+	// 7. Delete the rule and verify the account is denied again.
+	rr = doRequest(t, handler, "DELETE", fmt.Sprintf("/v1/policy/rules/%d", created.ID), nil, adminToken)
+	if rr.Code != http.StatusNoContent {
+		t.Fatalf("delete policy rule status = %d, want 204; body: %s", rr.Code, rr.Body.String())
+	}
+	rr = doRequest(t, handler, "GET", "/v1/accounts", nil, svcToken)
+	if rr.Code != http.StatusForbidden {
+		t.Errorf("system account (rule deleted) list accounts status = %d, want 403", rr.Code)
+	}
+}
+
+// TestPolicyDenyRule verifies that an explicit Deny rule blocks access even
+// when an Allow rule would otherwise permit it.
+func TestPolicyDenyRule(t *testing.T) {
+	srv, _, priv, _ := newTestServer(t)
+	handler := srv.Handler()
+
+	adminToken, _ := issueAdminToken(t, srv, priv, "admin-deny")
+
+	// Create an Allow rule for the system account.
+	svcToken, svcAcct := issueSystemToken(t, srv, priv, "svc-deny", []string{"user"})
+	allow := createPolicyRuleRequest{
+		Description: "allow svc-deny to list accounts",
+		Priority:    50,
+		Rule: policy.RuleBody{
+			SubjectUUID: svcAcct.UUID,
+			Actions:     []policy.Action{policy.ActionListAccounts},
+			Effect:      policy.Allow,
+		},
+	}
+	rr := doRequest(t, handler, "POST", "/v1/policy/rules", allow, adminToken)
+	if rr.Code != http.StatusCreated {
+		t.Fatalf("create allow rule status = %d; body: %s", rr.Code, rr.Body.String())
+	}
+
+	// Verify access is granted.
+	rr = doRequest(t, handler, "GET", "/v1/accounts", nil, svcToken)
+	if rr.Code != http.StatusOK {
+		t.Fatalf("with allow rule, list accounts status = %d, want 200", rr.Code)
+	}
+
+	// Add a higher-priority Deny rule for the same account.
+	deny := createPolicyRuleRequest{
+		Description: "deny svc-deny accounts:list",
+		Priority:    10, // lower number = higher precedence
+		Rule: policy.RuleBody{
+			SubjectUUID: svcAcct.UUID,
+			Actions:     []policy.Action{policy.ActionListAccounts},
+			Effect:      policy.Deny,
+		},
+	}
+	rr = doRequest(t, handler, "POST", "/v1/policy/rules", deny, adminToken)
+	if rr.Code != http.StatusCreated {
+		t.Fatalf("create deny rule status = %d; body: %s", rr.Code, rr.Body.String())
+	}
+
+	// Deny-wins: access must now be blocked despite the Allow rule.
+	rr = doRequest(t, handler, "GET", "/v1/accounts", nil, svcToken)
+	if rr.Code != http.StatusForbidden {
+		t.Errorf("deny-wins: list accounts status = %d, want 403", rr.Code)
+	}
+}