Api Key Exposure in Fiber with Basic Auth

Using HTTP Basic Authentication in a Fiber-based API can inadvertently expose API keys when credentials are handled or logged insecurely. Basic Auth encodes a username:password pair in Base64 and transmits it in the Authorization header. If the server uses this mechanism to carry an API key—such as treating the password as the key—no transport-layer protection (TLS) will hide the encoded value from anyone who can intercept or inspect traffic. Even with TLS, improper practices can leak the key in application logs, error messages, or via server misconfigurations.

In a black-box scan, middleBrick tests unauthenticated endpoints and checks whether credentials are transmitted in ways that can be captured or reused. When Basic Auth is used to convey an API key, the scanner observes the Authorization header in requests and responses, and can detect whether the key is embedded in a way that violates the principle of least privilege or separation of concerns. For example, sending an API key as the password means the key traverses every request in the clear (Base64-encoded), and any middleware, logging library, or debugging tool that captures headers may inadvertently store or expose it. This becomes especially risky if logs are centralized or if error pages reflect headers in debug output, which can happen in development or misconfigured production environments.

Additionally, if the Fiber application reuses the same credentials across services or fails to rotate keys, the exposure window expands. MiddleBrick’s checks for Data Exposure and Authentication evaluate whether credentials appear in responses, logs, or error payloads, and whether transport protections are consistent. A common insecure pattern is to set the password in the Basic Auth header directly from an environment variable without validation, then echo request details for debugging. Even if TLS is enforced, logging the Authorization header or including it in crash reports can expose the key to unauthorized parties.

Another vector involves SSRF and improper request handling. If user-supplied input is used to construct URLs for outbound HTTP requests and Basic Auth credentials are attached automatically, an attacker can force the server to make authenticated requests to internal services, potentially exfiltrating the key through SSRF-induced interactions. middleBrick tests for SSRF and checks whether authentication mechanisms are applied inconsistently across endpoints, which can lead to privilege escalation or unintended access.

Proper design avoids embedding secrets in Basic Auth passwords. Instead, use opaque tokens in headers, and if Basic Auth is required for compatibility, ensure the password is a long, random value rotated frequently, never a reusable API key. middleBrick’s Inventory Management and Data Exposure checks help identify whether credentials appear in responses or logs, and its Encryption checks verify TLS is enforced across all routes.

To remediate API key exposure when using Basic Auth in Fiber, refactor authentication so secrets are not embedded in credentials used for identification. Use opaque tokens passed in a dedicated header (e.g., X-API-Key) and validate them securely without logging or echoing them. If Basic Auth must be retained for compatibility, ensure the password is not a reusable key and enforce strict transport and logging controls.

Insecure pattern to avoid

// Insecure: using Basic Auth password as API key
package main

import (
	"fmt"
	"log"
	"net/http"

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

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

	// Middleware that extracts API key from Basic Auth password
	app.Use(func(c *fiber.Ctx) error {
		hdr := c.Get("Authorization")
		if len(hdr) == 0 {
			return c.Status(fiber.StatusUnauthorized).SendString("Authorization header required")
		}
		// Expecting "Basic base64(username:password)" where password is the API key
		// This exposes the key in logs and requests
		log.Printf("Received auth header: %s", hdr)
		// Further validation omitted for brevity
		return c.Next()
	})

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

	log.Fatal(app.Listen(":3000"))
}

Secure remediation with token-based validation

// Secure: use a dedicated header and avoid logging secrets
package main

import (
	"crypto/subtle")
	"fmt"
	"net/http"

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

const validAPIKey = "s3cr3t_k3y_xyz789" // In practice, load from secure vault/env

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

	// Secure middleware: validate X-API-Key without logging the key
	app.Use(func(c *fiber.Ctx) error {
		provided := c.Get("X-API-Key")
		if provided == "" {
			return c.Status(fiber.StatusUnauthorized).SendString("X-API-Key header required")
		}
		// Constant-time comparison to avoid timing attacks
		if subtle.ConstantTimeCompare([]byte(provided), []byte(validAPIKey)) != 1 {
			return c.Status(fiber.StatusForbidden).SendString("Invalid API key")
		}
		// Do not log the key; log only metadata
		// log.Printf("Authorized request from %s", c.IP())
		return c.Next()
	})

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

	// Enforce TLS in production (not shown here)
	log.Fatal(app.Listen(":3000"))
}

If Basic Auth must be used, enforce TLS and avoid key reuse

// Minimal secure Basic Auth usage: treat credentials as opaque, never as API keys
package main

import (
	"net/http"

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

func basicAuthMiddleware(expectedUser, expectedPass string) fiber.Handler {
	return func(c *fiber.Ctx) error {
		hdr := c.Get("Authorization")
		if len(hdr) == 0 {
			return c.Status(fiber.StatusUnauthorized).SendString("Authorization header required")
		}
		const prefix = "Basic "
		if len(hdr) < len(prefix) || hdr[:len(prefix)] != prefix {
			return c.Status(fiber.StatusBadRequest).SendString("Invalid authorization header format")
		}
		// Decode and split; in production use a constant-time compare for credentials
		// This example is illustrative; prefer token-based auth for API keys
		creds, err := base64.StdEncoding.DecodeString(hdr[len(prefix):])
		if err != nil {
			return c.Status(fiber.StatusBadRequest).SendString("Invalid base64")
		}
		pair := string(creds)
		// Expecting "user:pass" where pass is a rotating secret, not an API key
		// Do not log pair
		// Validate with constant-time comparison where possible
		if !validateBasicCreds(pair, expectedUser, expectedPass) {
			return c.Status(fiber.StatusForbidden).SendString("Invalid credentials")
		}
		return c.Next()
	}
}

func validateBasicCreds(pair, user, pass string) bool {
	// In real use, use constant-time comparison and avoid string split in timing-sensitive contexts
	// This is simplified for illustration
	expected := user + ":" + pass
	return subtle.ConstantTimeCompare([]byte(pair), []byte(expected)) == 1
}

func main() {
	app := fiber.New()
	app.Use(basicAuthMiddleware("apiuser", "rotating_secret_2025"))
	app.Get("/secure", func(c *fiber.Ctx) error {
		return c.SendString("OK")
	})
	// Enforce TLS in production
	log.Fatal(app.Listen(":3000"))
}

Key takeaways: avoid using API keys as Basic Auth passwords, prefer dedicated headers with opaque tokens, enforce TLS, and prevent logging or echoing secrets. middleBrick’s Authentication and Data Exposure checks can surface risky patterns by analyzing requests and responses for credential leakage.