Broken Authentication in Fiber with Api Keys

Broken Authentication in the Fiber Go framework often occurs when API keys are handled inconsistently across middleware and route handlers. In a typical pattern, a developer configures custom middleware that reads an Authorization: ApiKey <key> header, validates the key against a store (for example a map or database), and then calls next() only if the key is recognized. If the middleware fails to enforce authentication on sensitive routes—such as administrative endpoints, user profile updates, or token rotation endpoints—an attacker can perform unauthenticated access or escalate privileges.

A second common vulnerability is key leakage through logs, error messages, or HTTP referrers. For instance, logging the full request context including the header can expose API keys in plaintext if centralized logging or error reporting is not controlled. Additionally, if keys are transmitted over non-TLS channels or stored in insecure configuration files, interception or accidental disclosure becomes more likely. These practices violate secure authentication design because the integrity and confidentiality of the key are not guaranteed.

Insecure storage and weak generation of API keys exacerbate the issue. Short, predictable keys or keys derived from user information are easier to guess or brute-force. When combined with missing rate limiting, this enables automated enumeration attacks. Even if middleware exists, without proper rate limiting and monitoring, attackers can probe for valid keys at scale.

When scanning an unauthenticated attack surface with middleBrick, findings related to Broken Authentication in this context often highlight missing authentication on critical routes, improper key validation logic, or exposure of keys in logs and error responses. These checks complement the broader authentication and authorization assessments across the 12 security checks, including BOLA/IDOR and Privilege Escalation, by focusing on how API keys are integrated into the Fiber request lifecycle.

Using the OpenAPI/Swagger spec analysis, middleBrick cross-references declared security schemes with runtime behavior. If a spec defines an apiKey security scheme but certain paths lack the corresponding security requirement, the scanner flags this as a misconfiguration. This is especially important for specs using $ref and complex components, where missing or incomplete references can inadvertently leave endpoints unprotected.

To remediate Broken Authentication when using API keys in Fiber, ensure that authentication is enforced consistently and keys are handled securely throughout the application.

1. Enforce authentication on all sensitive routes

Define a reusable middleware that validates the API key and attach it to protected routes. Avoid relying on manual checks in each handler.

package main

import (
	"fmt"
	"strings"

	"github.com/gofiber/fiber/v2"
)

// apiKeyMiddleware validates the presence and correctness of an API key.
func apiKeyMiddleware(validKeys map[string]bool) func(*fiber.Ctx) error {
	return func(c *fiber.Ctx) error {
		auth := c.Get("Authorization")
		if auth == "" {
			return c.Status(fiber.StatusUnauthorized).JSON(fiber.Map{"error": "authorization header required"})
		}
		const prefix = "ApiKey "
		if !strings.HasPrefix(auth, prefix) {
			return c.Status(fiber.StatusUnauthorized).JSON(fiber.Map{"error": "invalid authorization format, expected ApiKey <key>"})
		}
		key := strings.TrimPrefix(auth, prefix)
		if !validKeys[key] {
			return c.Status(fiber.StatusForbidden).JSON(fiber.Map{"error": "invalid api key"})
		}
		return c.Next()
	}
}

func main() {
	validKeys := map[string]bool{
		"s3cr3tk3y123": true,
		"adminkey456":  true,
	}

	app := fiber.New()

	// Public route: no authentication required
	app.Get("/public", func(c *fiber.Ctx) error {
		return c.JSON(fiber.Map{"message": "public endpoint"})
	})

	// Protected routes: require valid API key
	protected := app.Group("/api")
	protected.Use(apiKeyMiddleware(validKeys))
	{
		protected.Get("/users", func(c *fiber.Ctx) error {
			return c.JSON(fiber.Map{"users": []string{"alice", "bob"}})
		})
		protected.Post("/admin/reset", func(c *fiber.Ctx) error {
			return c.JSON(fiber.Map{"status": "reset initiated"})
		})
	}

	// Start server
	if err := app.Listen(":3000"); err != nil {
		panic(err)
	}
}

2. Avoid key leakage and improve storage

Do not log the full Authorization header. If you must log requests, redact sensitive headers.

package main

import (
	"log"

	"github.com/gofiber/fiber/v2"
)

// safeLoggingMiddleware redacts sensitive headers before logging.
func safeLoggingMiddleware() func(*fiber.Ctx) error {
	return func(c *fiber.Ctx) error {
		// Log method and path, but redact Authorization
		log.Printf("req method=%s path=%s", c.Method(), c.Path())
		return c.Next()
	}
}

func main() {
	app := fiber.New()
	app.Use(safeLoggingMiddleware())

	app.Get("/health", func(c *fiber.Ctx) error {
		return c.SendString("ok")
	})

	app.Listen(":3000")
}

Prefer environment variables or secure configuration stores for valid keys rather than hardcoding them. Rotate keys periodically and invalidate compromised keys immediately.

3. Combine with rate limiting and monitoring

Add rate limiting to mitigate brute-force enumeration of API keys. This complements authentication by reducing the attack window for guessing valid keys.

package main

import (
	"github.com/gofiber/fiber/v2"
	"github.com/gofiber/fiber/v2/middleware/limiter"
	"golang.org/x/time/rate"
)

func main() {
	app := fiber.New()

	// Allow 10 requests per second per IP as a baseline.
	app.Use(limiter.New(limiter.Config{
		Rate:         rate.Limit(10),
		BucketSize:   10,
		KeyGenerator: func(c *fiber.Ctx) (string, error) {
			return c.IP(), nil
		},
	}))

	app.Get("/api/data", func(c *fiber.Ctx) error {
		return c.JSON(fiber.Map{"data": "value"})
	})

	app.Listen(":3000")
}

These steps ensure that API keys are required where appropriate, transmitted and stored safely, and that brute-force attacks are mitigated, reducing the risk of Broken Authentication in a Fiber API using API keys.