Broken Authentication in Fiber (Go)

Broken Authentication in a Fiber service written in Go commonly arises from insecure session handling, weak token implementations, or missing validation checks that are easy to overlook when using convenience features of the framework. Fiber is a fast, expressive web framework for Go, and while it does not enforce a specific authentication mechanism, developers must make deliberate choices to avoid introducing vulnerabilities.

One typical scenario involves session cookies without the HttpOnly, Secure, and SameSite flags set, which can expose session identifiers to theft via cross-site scripting (XSS) or insecure transmission. For example, a cookie set without Secure on non-HTTPS endpoints can be intercepted in transit. Another common issue is storing sensitive data, such as user roles or identifiers, in the client-side cookie without integrity protection, enabling tampering attacks that lead to privilege escalation.

JWT-based authentication is also popular in Go Fiber projects. Broken Authentication can occur when tokens are issued with weak signing algorithms (e.g., using none or HS256 with a shared secret exposed in client code), have long expiration times without refresh token rotation, or do not validate claims such as iss, aud, and exp. If middleware does not properly verify the token signature and required claims, an attacker can forge tokens and impersonate users.

Additionally, missing or misconfigured rate limiting on authentication endpoints can enable credential stuffing or brute-force attacks. Since Fiber allows developers to add middleware flexibly, omitting global or route-specific rate limits on login and password-reset endpoints increases the risk of automated abuse. The combination of a high-performance framework like Fiber and the Go ecosystem can inadvertently encourage shortcuts in security practices, such as skipping secure cookie attributes or skipping validation steps, which lead to exploitable authentication flaws.

To remediate Broken Authentication in Fiber with Go, apply secure defaults and validate all authentication inputs and outputs. Below are concrete code examples demonstrating secure session cookies and JWT validation middleware.

Securing Session Cookies

Ensure cookies include HttpOnly, Secure, and SameSite attributes. This reduces the risk of token theft via XSS and ensures cookies are only sent over HTTPS.

// Secure cookie setup in Fiber
app.Get("/login", func(c *fiber.Ctx) error {
    // After successful authentication
    cookie := &fiber.Cookie{
        Name:     "session_id",
        Value:    generateSessionToken(),
        Expires:  time.Now().Add(24 * time.Hour),
        HTTPOnly: true,
        Secure:   true,       // Only over HTTPS
        SameSite: fiber.CookieSameSiteLaxMode,
        Path:     "/",
    }
    c.Cookie(cookie)
    return c.SendString("Logged in")
})

JWT Validation Middleware

Use a well-maintained JWT library such as `golang-jwt/jwt` and enforce algorithm validation and claim checks. Avoid accepting tokens signed with the none algorithm.

import (
    "github.com/golang-jwt/jwt/v5"
    "github.com/gvalle/jwt-go/fiber"
)

func JWTMiddleware() fiber.Handler {
    return func(c *fiber.Ctx) error {
        auth := c.Get("Authorization")
        if auth == "" {
            return c.SendStatus(fiber.StatusUnauthorized)
        }

        tokenString := auth[len("Bearer "):]
        token, err := jwt.Parse(tokenString, func(token *jwt.Token) (interface{}, error) {
            // Ensure the signing method is as expected
            if _, ok := token.Method.(*jwt.SigningMethodHMAC); !ok {
                return nil, fmt.Errorf("unexpected signing method: %v", token.Header["alg"])
            }
            return []byte("your-256-bit-secret"), nil
        })

        if err != nil || !token.Valid {
            return c.SendStatus(fiber.StatusUnauthorized)
        }

        // Validate standard claims
        if claims, ok := token.Claims.(jwt.MapClaims); ok {
            if !claims.VerifyIssuer("my-service", true) {
                return c.SendStatus(fiber.StatusUnauthorized)
            }
            if !claims.VerifyAudience("https://api.example.com", true) {
                return c.SendStatus(fiber.StatusUnauthorized)
            }
            if claims.VerifyExpiresAt(time.Now().Unix(), true) != nil {
                return c.SendStatus(fiber.StatusUnauthorized)
            }
        }

        c.Locals("user", token)
        return c.Next()
    }
}

Rate Limiting on Authentication Endpoints

Apply rate limiting to login and password-reset routes to mitigate brute-force and credential stuffing attacks.

import (
    "github.com/gofiber/contrib/ratelimit"
    "time"
)

// Apply rate limiting to the login route
app.Post("/login", ratelimit.New(ratelimit.Config{
    Max:           5,               // 5 requests
    Expiration:    1 * time.Minute, // per minute
    Message:       "Too many attempts",
}), func(c *fiber.Ctx) error {
    // Handle login logic
    return c.SendString("attempt logged")
})

These Go-specific practices align with the checks in middleBrick’s Authentication, BOLA/IDOR, and Rate Limiting assessments, helping you detect and address misconfigurations before they are flagged as high-risk findings.