gofiber/fiber · error

fiber: keyauth middleware requires a validator function

Error message

fiber: keyauth middleware requires a validator function

What it means

keyauth.New() panics when called with no Config argument at all. Because Validator is the only required field and cannot have a sensible default, calling New() with zero arguments is treated as a programmer error: the middleware has no way to decide which keys are valid. The same message is reused for the nil-Validator case (error 287) but this specific line fires on len(config) < 1.

Solutions

1. Pass a Config with a Validator: keyauth.New(keyauth.Config{Validator: func(c fiber.Ctx, key string) (bool, error){ ... }}).
2. If you are just scaffolding, comment out the app.Use(keyauth.New()) line until the Validator is ready.
3. Ensure any helper that builds keyauth config always returns a non-nil Validator before the result reaches New().

Example fix

// before
app.Use(keyauth.New())

// after
app.Use(keyauth.New(keyauth.Config{
    Validator: func(_ fiber.Ctx, key string) (bool, error) {
        return key == os.Getenv("API_KEY"), nil
    },
}))

func mustKeyAuth(validator func(fiber.Ctx, string) (bool, error)) fiber.Handler {
    if validator == nil {
        log.Fatal("keyauth requires a validator")
    }
    return keyauth.New(keyauth.Config{Validator: validator})
}

func hasKeyAuthConfig(args ...keyauth.Config) bool { return len(args) > 0 }

When it happens

Trigger: keyauth.New() with no arguments. Also any wrapper that does var cfg keyauth.Config; keyauth.New(cfg) would NOT hit this line (it has len 1) — only a truly empty variadic call does.

Common situations: Adding app.Use(keyauth.New()) as a placeholder during scaffolding and forgetting to come back; refactor that moves Config construction into a function returning zero values; conditional wiring where the config-arg branch is dropped.

Related errors

• fiber: keyauth error_description requires error
• fiber: keyauth error_uri must be absolute
• fiber: keyauth error_uri requires error
• fiber: keyauth insufficient_scope requires scope
• fiber: keyauth scope contains invalid token

AI-assisted analysis of gofiber/fiber@a105acad6c (2026-08-11). Data as JSON: /api/errors/7b7ccc353cce8004. Report an issue: GitHub.

Appendix: source

Thrown at middleware/keyauth/config.go:105

}

// ConfigDefault is the default config
var ConfigDefault = Config{
	SuccessHandler: func(c fiber.Ctx) error {
		return c.Next()
	},
	ErrorHandler: func(c fiber.Ctx, _ error) error {
		return c.Status(fiber.StatusUnauthorized).SendString(ErrMissingOrMalformedAPIKey.Error())
	},
	Realm:     "Restricted",
	Extractor: extractors.FromAuthHeader("Bearer"),
}

// configDefault is a helper function to set default values
func configDefault(config ...Config) Config {
	// Return default config if nothing provided
	if len(config) < 1 {
		panic("fiber: keyauth middleware requires a validator function")
	}
	cfg := config[0]

	// Require a validator function
	if cfg.Validator == nil {
		panic("fiber: keyauth middleware requires a validator function")
	}

	// Set default values
	if cfg.Extractor.Extract == nil {
		cfg.Extractor = ConfigDefault.Extractor
	}
	if cfg.Realm == "" {
		cfg.Realm = ConfigDefault.Realm
	}
	if cfg.SuccessHandler == nil {
		cfg.SuccessHandler = ConfigDefault.SuccessHandler
	}

View on GitHub (pinned to a105acad6c)