Broken Access Control in Buffalo with Api Keys

Broken Access Control occurs when authorization checks are missing, incomplete, or bypassed, allowing a user to access or modify resources they should not. In the Buffalo framework, this risk is amplified when API keys are used for authentication but authorization is not enforced on every sensitive endpoint. API keys are typically bearer tokens: if they are accepted without verifying scope, role, or tenant boundaries, an authenticated client can perform actions or view data belonging to other clients.

Consider a Buffalo application that protects routes with an API key middleware but then relies on the controller to decide what a user can see. If a handler does not validate that the resource’s owner matches the key’s associated identity (or tenant), an attacker who knows or guesses another resource ID can exploit Insecure Direct Object References (IDOR) or BOLA (Broken Level of Authorization). For example, an API key issued to customer A might still reach customer B’s records because the handler trusted the key alone and skipped ownership checks. This becomes a BFLA (Broken Function Level Authorization) pattern when administrative endpoints do not verify a key is scoped to admin privileges, allowing privilege escalation across roles.

Buffalo’s convention-based routing and parameter parsing can unintentionally expose these gaps. When developers use params.All() or bind parameters directly to models without confirming the requester’s right to that specific identifier, they risk leaking or mutating data across authorization boundaries. Real-world attack patterns such as IDOR in /api/v1/users/:id or BOLA in /api/v1/organizations/:org_id/billing are common when authorization is treated as an afterthought. The impact can include viewing sensitive data, modifying other users’ records, or invoking admin functions by simply changing an ID in the URL.

OpenAPI/Swagger analysis helps highlight these issues by cross-referencing spec definitions with runtime findings. If paths that should be restricted do not explicitly document required scopes or roles, and the runtime tests do not validate authorization for different keys, the API’s unauthenticated attack surface reveals missing authorization checks. This is distinct from authentication: the key may be valid, but the authorization logic is insufficient. Tools like middleBrick can detect these patterns by running checks such as BOLA/IDOR and Property Authorization against your Buffalo endpoints, mapping findings to OWASP API Top 10 controls and helping you understand where access control rules must be enforced.

To fix Broken Access Control with API keys in Buffalo, enforce authorization on every handler, validate resource ownership, and scope keys to the correct permissions. Below are concrete code examples that demonstrate a secure approach.

1. Middleware that loads and validates the API key, attaching tenant or scope information to the context for downstream use.

// app/middleware/api_key_auth.go
package middleware

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

// APIKeyAuth ensures a valid API key is present and enforces scope checks.
func APIKeyAuth(next buffalo.Handler) buffalo.Handler {
    return func(c buffalo.Context) error {
        key := c.Request().Header.Get("Authorization")
        if key == "" {
            return c.Render(401, r.JSON(map[string]string{"error": "authorization header required"}))
        }
        // Validate key format and lookup; in production, use a secure store.
        if !isValidKey(key) {
            return c.Render(403, r.JSON(map[string]string{"error": "invalid api key"}))
        }
        // Attach metadata to context for authorization decisions later.
        c.Set("api_key_scopes", getScopesForKey(key))
        c.Set("api_key_tenant", getTenantForKey(key))
        return next(c)
    }
}

func isValidKey(key string) bool {
    // Replace with secure lookup (e.g., database, vault).
    validKeys := map[string]bool{
        "ak_live_abc123": true,
        "ak_test_xyz789": true,
    }
    return validKeys[key]
}

func getScopesForKey(key string) []string {
    scopes := map[string][]string{
        "ak_live_abc123": {"admin", "billing"},
        "ak_test_xyz789": {"read"},
    }
    return scopes[key]
}

func getTenantForKey(key string) string {
    tenants := map[string]string{
        "ak_live_abc123": "tenant_alpha",
        "ak_test_xyz789": "tenant_beta",
    }
    return tenants[key]
}

2. A handler that checks ownership and scope before acting on a resource, preventing IDOR and BOLA.

// app/handlers/users.go
package handlers

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

func ShowUser(c buffalo.Context) error {
    requestedID, err := strconv.Atoi(c.Param("user_id"))
    if err != nil {
        return c.Render(400, r.JSON(map[string]string{"error": "invalid user id"}))
    }
    currentTenant := c.Get("api_key_tenant").(string)
    // Enforce tenant-based scoping: ensure the requested user belongs to the same tenant.
    user, err := UserByTenantAndID(currentTenant, requestedID)
    if err != nil {
        return c.Render(404, r.JSON(map[string]string{"error": "user not found"}))
    }
    // Optionally enforce scope checks for sensitive actions.
    if !hasScope(c, "admin") && user.ID != currentUserIDFromContext(c) {
        return c.Render(403, r.JSON(map[string]string{"error": "access denied"}))
    }
    return c.Render(200, r.JSON(user))
}

func hasScope(c buffalo.Context, scope string) bool {
    scopes, ok := c.Get("api_key_scopes").([]string)
    if !ok {
        return false
    }
    for _, s := range scopes {
        if s == scope {
            return true
        }
    }
    return false
}

3. Apply the middleware globally or to specific routes in your Buffalo application.

// app/app.go
func app() *buffalo.App {
    if app == nil {
        app = buffalo.New(buffalo.Options{
            Env:         ENV,
            SessionStore: &sessions.NullStore{},
        })
        app.Use(APIKeyAuth) // secure all routes by default
        app.GET("/users/:user_id", ShowUser)
        app.GET("/admin/dashboard", AdminDashboard)
    }
    return app
}

These examples ensure that API keys are validated, tenant and scope metadata are used for authorization decisions, and resource ownership is verified on every request. This combination directly addresses Broken Access Control by making authorization checks mandatory and explicit, reducing the risk of IDOR, BOLA, and privilege escalation via insecure API key usage.