Broken Authentication in Fiber with Jwt Tokens

Broken Authentication in the Fiber web framework when using JWT tokens typically occurs due to insecure token handling, missing validation, or improper middleware configuration. Because Fiber is a fast, extensible Go framework, developers often integrate JWT-based authentication via middleware or custom handlers. If these integrations are implemented without strict validation, the application can be vulnerable to authentication bypass, token tampering, or insecure token storage.

For example, if a route is protected only by checking for the presence of a token rather than validating its signature, issuer, or expiration, an attacker can supply any string as a token and gain unauthorized access. This maps to the broader BOLA/IDOR and Authentication checks performed by middleBrick, where unauthenticated attack surfaces are tested to identify weak access controls. A common real-world pattern involves using the jwt-go library with an algorithm set to none during development or misconfigured to accept unsigned tokens in production.

Another vulnerability scenario involves not validating the aud (audience) or iss (issuer) claims, allowing a token issued for one service to be accepted by another. If the application does not enforce HTTPS, tokens can be intercepted via man-in-the-middle attacks. middleBrick’s authentication and encryption checks help detect such misconfigurations by analyzing the unauthenticated endpoint surface and inspecting OpenAPI specs for security-related metadata like securitySchemes and transport guarantees.

Additionally, storing JWTs in local storage or insecure cookies without the HttpOnly and Secure flags can lead to cross-site scripting (XSS) based token theft. When combined with weak input validation, this enables attackers to inject malicious scripts that steal session tokens. The LLM/AI Security checks in middleBrick specifically look for endpoints lacking proper authentication schemes or exposing tokens in logs or error messages, which could lead to system prompt leakage or unauthorized access in AI-integrated services.

Using middleBrick’s CLI tool, you can scan a Fiber API endpoint with JWT authentication to uncover these issues: middlebrick scan https://api.example.com. The tool reports whether authentication checks are correctly enforced and whether tokens are transmitted securely, aligning with findings from the Authentication and Encryption categories.

To remediate Broken Authentication when using JWT tokens in Fiber, enforce strict token validation, use secure transport, and apply least-privilege access controls. Below are concrete, working code examples that demonstrate secure JWT handling in a Fiber application.

First, always validate the token signature and claims. Use a well-maintained library such as golang-jwt/jwt/v5 and avoid algorithms like SigningMethodNone. The example below shows how to parse and validate a JWT before allowing access to a protected route:

package main

import (
	"github.com/gofiber/fiber/v2"
	"github.com/gofiber/fiber/v2/middleware/jwt"
	"github.com/golang-jwt/jwt/v5"
)

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

	config := jwt.Config{
		SigningKey:   jwt.SigningKey{Key: []byte("your-256-bit-secret")},
		ContextKey:   "user",
		SigningMethod: "HS256",
		Validator: func(token *jwt.Token) (interface{}, error) {
			if _, ok := token.Method.(*jwt.SigningMethodHMAC); !ok {
				return nil, fiber.ErrUnauthorized
			}
			return []byte("your-256-bit-secret"), nil
		},
	}

	app.Get("/protected", config.Handler(), func(c *fiber.Ctx) error {
		user := c.Locals("user").(*jwt.Token)
		claims := user.Claims.(jwt.MapClaims)
		return c.JSON(fiber.Map{
			"message": "access granted",
			"user_id": claims["user_id"],
		})
	})

	app.Listen(":3000")
}

Second, ensure tokens are transmitted only over HTTPS and that cookies include Secure and HttpOnly flags if stored client-side. When issuing tokens, set short expiration times and use refresh tokens stored securely server-side. The following snippet shows how to set a secure cookie with a JWT:

app.Get("/login", func(c *fiber.Ctx) error {
	token := jwt.New(jwt.SigningMethodHS256)
	token.Claims = jwt.MapClaims{
		"user_id": 123,
		"exp":     time.Now().Add(time.Hour * 72).Unix(),
	}
	tokenString, _ := token.SignedString([]byte("your-256-bit-secret"))

	c.Cookie(&fiber.Cookie{
		Name:     "access_token",
		Value:    tokenString,
		Expires:  time.Now().Add(time.Hour * 72),
		HTTPOnly: true,
		Secure:   true,
		SameSite: fiber.CookieSameSiteStrictMode,
	})
	return c.SendStatus(fiber.StatusOK)
})

Finally, integrate middleBrick’s GitHub Action to enforce security gates in CI/CD: add the action to your workflow and set a threshold so that any PR with a risk score above your defined level fails the build. This ensures that misconfigurations in JWT handling are caught before deployment. For ongoing protection, use the Pro plan’s continuous monitoring to detect changes in authentication behavior across deployed versions of your Fiber API.