✨ feat(auth): JWT TTL hot-reload + fix hardcoded 24h bug (ADR-0023 Phase 2)

Two changes in one diff because they share the same surface (JWTConfig
plumbing):

1. **Bug fix** : pkg/server/server.go was hardcoding ExpirationTime to
   24h, ignoring the auth.jwt.ttl config value entirely (default 1h).
   Production has been signing tokens with 24h TTL regardless of config
   since the config field was added.

2. **Hot-reload (ADR-0023 Phase 2)** : extends JWTConfig with a GetTTL
   func() time.Duration callback. effectiveTTL() prefers GetTTL when
   set, falls back to ExpirationTime otherwise (test-friendly). server.go
   wires GetTTL = cfg.GetJWTTTL — a method value that captures the
   *Config, so when WatchAndApply re-unmarshals, the next token
   generation reads the new TTL automatically. Tokens already issued
   keep their original expiry.

WatchAndApply now also logs the new jwt_ttl on every reload event.

Tests:
- New TestWatchAndApply_JWTTTL in pkg/config/config_hot_reload_test.go
  rewrites the config file and asserts the in-memory ttl flips within
  2s. Polling (no fixed sleep), race-clean.
- Existing pkg/user tests (including JWT manager + cleanup loop) all
  pass with -race.
- Full BDD suite (auth/config/greet/health/info/jwt) green.

ADR-0023 status: Phase 1+2 Implemented. Phase 3 (telemetry sampler)
and Phase 4 (api.v2_enabled — needs router refactor) remain Proposed.

adr/0023-config-hot-reloading.md

@@ -1,6 +1,6 @@
 # Config Hot Reloading Strategy
 
-**Status:** Phase 1 Implemented (2026-05-05 — `logging.level` hot-reloadable via `Config.WatchAndApply` in `pkg/config/config.go`, wired in `pkg/server/server.go Run`. Remaining fields — `api.v2_enabled`, telemetry sampler, `auth.jwt.ttl` — Proposed for follow-up phases following the same pattern.)
+**Status:** Phase 1+2 Implemented (2026-05-05 — `logging.level` and `auth.jwt.ttl` hot-reloadable via `Config.WatchAndApply` in `pkg/config/config.go`, wired in `pkg/server/server.go Run`. Phase 2 also fixed a pre-existing bug where the hardcoded 24h TTL ignored `auth.jwt.ttl` from config entirely. Remaining fields — `api.v2_enabled`, telemetry sampler — Proposed for follow-up phases.)
 **Authors:** Gabriel Radureau, AI Agent
 **Date:** 2026-04-05
 **Last Updated:** 2026-05-05

pkg/config/config.go

@@ -609,11 +609,15 @@ func (c *Config) setupLogOutput() {
 // WatchAndApply starts watching the config file for changes and applies the
 // hot-reloadable subset on every change (ADR-0023 selective hot-reload).
 //
-// Phase 1 (this PR) reloads:
-//   - logging.level — re-applies via SetupLogging on every change.
+// Phases shipped:
+//   - Phase 1: logging.level — re-applied via SetupLogging on every change.
+//   - Phase 2: auth.jwt.ttl — picked up automatically because the userService
+//     reads it via JWTConfig.GetTTL (a method value capturing this *Config).
+//     The reloaded TTL is used on the NEXT token generation; tokens issued
+//     before the change keep their original expiry.
 //
-// The other fields listed in ADR-0023 (api.v2_enabled, telemetry sampler,
-// auth.jwt.ttl) remain restart-only until their handlers land in a follow-up.
+// The other fields listed in ADR-0023 (api.v2_enabled, telemetry sampler)
+// remain restart-only until their handlers land in subsequent phases.
 //
 // Stops when ctx is cancelled. Safe to call once at server startup.
 // If the config file is absent (ConfigFileNotFoundError at load time), this
@@ -641,7 +645,10 @@ func (c *Config) WatchAndApply(ctx context.Context) {
 		// Apply hot-reloadable fields. Order matters: logging first so the
 		// rest of the reload is logged at the right level.
 		c.SetupLogging()
-		log.Info().Str("logging_level", c.GetLogLevel()).Msg("Hot-reload applied (logging.level)")
+		log.Info().
+			Str("logging_level", c.GetLogLevel()).
+			Dur("jwt_ttl", c.GetJWTTTL()).
+			Msg("Hot-reload applied (logging.level + auth.jwt.ttl)")
 	})
 	c.viper.WatchConfig()
 

pkg/config/config_hot_reload_test.go

@@ -21,6 +21,7 @@ func loadFromFile(t *testing.T, path string) *Config {
 	v.SetConfigFile(path)
 	v.SetConfigType("yaml")
 	v.SetDefault("logging.level", "info")
+	v.SetDefault("auth.jwt.ttl", time.Hour)
 	require.NoError(t, v.ReadInConfig())
 
 	c := &Config{viper: v}
@@ -81,3 +82,35 @@ func TestWatchAndApply_NilViperNoOp(t *testing.T) {
 	defer cancel()
 	c.WatchAndApply(ctx)
 }
+
+// TestWatchAndApply_JWTTTL proves Phase 2 of ADR-0023: the JWT TTL is
+// re-read on every token generation via the GetJWTTTL method value, so
+// after a config-file change the new TTL takes effect without restart.
+func TestWatchAndApply_JWTTTL(t *testing.T) {
+	dir := t.TempDir()
+	path := filepath.Join(dir, "config.yaml")
+	require.NoError(t, os.WriteFile(path, []byte("auth:\n  jwt:\n    ttl: 1h\n"), 0644))
+
+	c := loadFromFile(t, path)
+	assert.Equal(t, time.Hour, c.GetJWTTTL())
+
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+	c.WatchAndApply(ctx)
+
+	require.NoError(t, os.WriteFile(path, []byte("auth:\n  jwt:\n    ttl: 30m\n"), 0644))
+
+	deadline := time.Now().Add(2 * time.Second)
+	for time.Now().Before(deadline) {
+		c.reloadMu.RLock()
+		ttl := c.GetJWTTTL()
+		c.reloadMu.RUnlock()
+		if ttl == 30*time.Minute {
+			return
+		}
+		time.Sleep(20 * time.Millisecond)
+	}
+	c.reloadMu.RLock()
+	defer c.reloadMu.RUnlock()
+	t.Fatalf("auth.jwt.ttl did not hot-reload to 30m: still %s", c.GetJWTTTL())
+}

pkg/server/server.go

@@ -139,10 +139,16 @@ func initializeUserServices(cfg *config.Config) (user.UserRepository, user.UserS
 		return nil, nil, fmt.Errorf("failed to create PostgreSQL user repository: %w", err)
 	}
 
-	// Create JWT config
+	// Create JWT config.
+	// GetTTL is a method value — it captures cfg, so when WatchAndApply
+	// re-unmarshals into the same Config struct on file changes, every
+	// subsequent token generation reads the new TTL (ADR-0023 Phase 2).
+	// ExpirationTime is kept as a static fallback for tests that build
+	// JWTConfig manually without a Config.
 	jwtConfig := user.JWTConfig{
 		Secret:         cfg.GetJWTSecret(),
-		ExpirationTime: time.Hour * 24, // 24 hours
+		ExpirationTime: 24 * time.Hour,
+		GetTTL:         cfg.GetJWTTTL,
 		Issuer:         "dance-lessons-coach",
 	}
 

pkg/user/auth_service.go

@@ -11,13 +11,30 @@ import (
 	"golang.org/x/crypto/bcrypt"
 )
 
-// JWTConfig holds JWT configuration
+// JWTConfig holds JWT configuration.
+//
+// GetTTL, when non-nil, is called on every token generation to read the
+// current TTL — this enables ADR-0023 Phase 2 hot-reload of `auth.jwt.ttl`.
+// If nil, ExpirationTime is used as a static fallback.
 type JWTConfig struct {
 	Secret         string
 	ExpirationTime time.Duration
+	GetTTL         func() time.Duration
 	Issuer         string
 }
 
+// effectiveTTL returns the live TTL: GetTTL() when wired, else
+// ExpirationTime as a static fallback (used by tests that don't go
+// through the server-level wiring).
+func (c JWTConfig) effectiveTTL() time.Duration {
+	if c.GetTTL != nil {
+		if ttl := c.GetTTL(); ttl > 0 {
+			return ttl
+		}
+	}
+	return c.ExpirationTime
+}
+
 // userServiceImpl implements the unified UserService interface
 type userServiceImpl struct {
 	repo           UserRepository
@@ -69,7 +86,7 @@ func (s *userServiceImpl) GenerateJWT(ctx context.Context, user *User) (string,
 		"sub":   user.ID,
 		"name":  user.Username,
 		"admin": user.IsAdmin,
-		"exp":   time.Now().Add(s.jwtConfig.ExpirationTime).Unix(),
+		"exp":   time.Now().Add(s.jwtConfig.effectiveTTL()).Unix(),
 		"iat":   time.Now().Unix(),
 		"iss":   s.jwtConfig.Issuer,
 	}