Integrity Failures in Buffalo with Bearer Tokens

An integrity failure in Buffalo occurs when a Bearer Token is accepted over an unencrypted HTTP endpoint or when the token is not adequately protected against tampering and replay. Buffalo applications that terminate TLS at a load balancer but do not enforce HTTPS-to-the-application layer can expose Bearer Tokens to on-path modification, enabling an attacker to inject or alter the token in transit. This violates the integrity guarantee that a Bearer Token must be transmitted and accepted exactly as issued.

Buffalo typically uses secure cookies for session management, but developers sometimes opt for Bearer Tokens in API-style endpoints (e.g., JSON APIs consumed by mobile clients). When such endpoints skip authenticity verification or rely solely on the presence of a token without validating its scope, binding, or freshness, integrity failures arise. For example, an attacker who can tamper with an unsigned or weakly signed token can escalate privileges by modifying claims, or they can replay a valid token if integrity checks like nonce or timestamp validation are absent.

Another common pattern is accepting Bearer Tokens via query parameters or non-HTTPS headers. Query strings are logged in server access logs and browser history, breaking integrity and confidentiality. Headers like Authorization: Bearer <token> should be the only acceptable carrier, and the application must reject tokens sent via alternate mechanisms. Buffalo applications must also ensure that any middleware or reverse proxy preserves the original Authorization header and does not inadvertently downgrade or replace it with an insecure alternative.

Real-world attack patterns include session fixation via token manipulation and privilege escalation by altering role claims in poorly validated tokens. Even if the token is cryptographically signed, integrity requires that the application validates the signature, checks the audience and issuer, and binds the token to the requesting client context. Without these checks, an attacker can exploit misconfigured CORS or referrer policies to steal or tamper with tokens, leading to unauthorized access that the Buffalo application treats as legitimate.

To detect such issues, middleBrick runs checks aligned with OWASP API Top 10 API5:2023 (Broken Function Level Authorization) and data exposure risks specific to token handling. The scanner tests unauthenticated endpoints that accept Bearer Tokens, verifies transport security, and inspects whether integrity mechanisms like signature validation and replay prevention are enforced. This helps identify configurations where Bearer Tokens are accepted over HTTP, passed in unsafe locations, or accepted without sufficient integrity guarantees.

Remediation focuses on enforcing HTTPS, validating token integrity, and ensuring tokens are handled only through secure headers. Below are concrete code examples for a Buffalo application using Go and the Buffalo framework.

1. Enforce HTTPS and reject HTTP requests with Bearer Tokens

Ensure your Buffalo app redirects HTTP to HTTPS and rejects requests with Bearer Tokens over non-secure channels.

// app/middleware/secure_redirect.go
package middleware

import (
    "github.com/gobuffalo/buffalo"
    "net/http"
)

// ForceHTTPS ensures all requests use HTTPS and rejects insecure token usage.
func ForceHTTPS(next buffalo.Handler) buffalo.Handler {
    return func(c buffalo.Context) error {
        if c.Request().Header.Get("X-Forwarded-Proto") == "http" {
            // Reject requests with Authorization header on HTTP
            if auth := c.Request().Header.Get("Authorization"); auth != "" {
                return c.Render(http.StatusForbidden, r.Text("HTTPS required"))
            }
            // Redirect to HTTPS for non-API clients if appropriate
            return c.Redirect(301, "https://"+c.Request().Host+c.Request().RequestURI)
        }
        return next(c)
    }
}

Add this middleware early in your stack:

// app/app.go
func app() *buffalo.App {
    if app == nil {
        app = buffalo.New(buffalo.Options{
            Env:         ENV,
            SessionStore: &middleware.SessionStore{},
        })
        app.Use(middleware.ForceHTTPS)
        // ... other middleware and routes
    }
    return app
}

2. Validate Bearer Token integrity and binding

Ensure tokens are validated for signature, audience, issuer, and replay resistance. Use a well-audited JWT library and bind tokens to the request context.

// app/middleware/bearer_auth.go
package middleware

import (
    "context"
    "net/http"

    "github.com/gobuffalo/buffalo"
    "github.com/golang-jwt/jwt/v5"
)

func BearerAuth(next buffalo.Handler) buffalo.Handler {
    return func(c buffalo.Context) error {
        auth := c.Request().Header.Get("Authorization")
        if auth == "" {
            return c.Render(http.StatusUnauthorized, r.Text("missing authorization header"))
        }
        const prefix = "Bearer "
        if len(auth) < len(prefix) || auth[:len(prefix)] != prefix {
            return c.Render(http.StatusUnauthorized, r.Text("invalid authorization header format"))
        }
        tokenString := auth[len(prefix):]

        token, err := jwt.Parse(tokenString, func(token *jwt.Token) (interface{}, error) {
            // TODO: use a proper key retrieval method, e.g., JWK set
            return []byte("your-256-bit-secret"), nil
        })
        if err != nil || !token.Valid {
            return c.Render(http.StatusUnauthorized, r.Text("invalid token"))
        }

        // Validate claims: audience, issuer, exp, nbf, and custom integrity claims
        if claims, ok := token.Claims.(jwt.MapClaims); ok {
            if aud, ok := claims["aud"].(string); !ok || aud != "your-api-audience" {
                return c.Render(http.StatusForbidden, r.Text("invalid audience"))
            }
            if iss, ok := claims["iss"].(string); !ok || iss != "https://auth.example.com" {
                return c.Render(http.StatusForbidden, r.Text("invalid issuer"))
            }
            // Optional: bind token to session or client context to prevent replay
            c.Set("token_claims", claims)
        }

        return next(c)
    }
}

Apply this middleware to routes that require Bearer Token integrity:

// app/controllers/api_controller.go
func (v APIController) SecureAction(c buffalo.Context) error {
    // token claims are available via c.Get("token_claims")
    return c.Render(200, r.JSON(map[string]string{"status": "secure"}))
}

3. Avoid unsafe transport of Bearer Tokens

Never accept Bearer Tokens in query parameters or fragments. Ensure logs do not capture tokens, and enforce strict header-only usage.

// app/middleware/no_query_token.go
package middleware

import (
    "net/http"

    "github.com/gobuffalo/buffalo"
)

func RejectTokenInQuery(next buffalo.Handler) buffalo.Handler {
    return func(c buffalo.Context) error {
        if c.Request().URL.Query().Get("access_token") != "" {
            return c.Render(http.StatusBadRequest, r.Text("tokens must not be in query parameters"))
        }
        // Also check fragment for client-side safety
        if c.Request().URL.Fragment != "" && containsTokenLike(c.Request().URL.Fragment) {
            return c.Render(http.StatusBadRequest, r.Text("tokens must not be in fragment"))
        }
        return next(c)
    }
}

func containsTokenLike(s string) bool {
    // naive check; adjust to your token format
    return len(s) > 10
}

Register this middleware before routing to ensure unsafe tokens are rejected early.

4. Use secure cookies for session-bound Bearer patterns if applicable

If you issue short-lived Bearer Tokens via authenticated sessions, store them in secure, HttpOnly cookies rather than exposing them to JavaScript or logs.

// app/middleware/session_token.go
package middleware

import (
    "net/http"

    "github.com/gobuffalo/buffalo"
    "github.com/gobuffalo/buffalo/sessions"
)

func SessionToken(next buffalo.Handler) buffalo.Handler {
    return func(c buffalo.Context) error {
        session, _ := c.Session()
        if token, ok := session.Get("bearer_token").(string); ok && token != "" {
            c.Response().Header().Set("Authorization", "Bearer "+token)
        }
        return next(c)
    }
}

// When setting the session token after login:
session := sessions.NewSession()
session.Add(&sessions.Session{Key: "bearer_token", Value: "short-lived-token", Options: &sessions.Options{
    Secure:   true,
    HttpOnly: true,
    SameSite: http.SameSiteStrictMode,
}})
c.Session().Add(session)

These patterns help maintain token integrity by ensuring transport security, strict validation, and safe handling practices within Buffalo applications.