Fix gosec, govet, and errorlint linter errors

Co-authored-by: Junie <junie@jetbrains.com>

internal/auth/auth.go

@@ -36,9 +36,8 @@ type cachedClaims struct {
 type Authenticator struct {
 	client *mcias.Client
 	logger *slog.Logger
-
-	mu    sync.RWMutex
-	cache map[string]*cachedClaims // keyed by SHA-256(token)
+	cache  map[string]*cachedClaims
+	mu     sync.RWMutex
 }
 
 // NewAuthenticator creates a new authenticator with the given MCIAS client.