Bola Idor in Chi with Api Keys

Broken Object Level Authorization (BOLA) in Chi when API keys are used centers on insufficient ownership checks between the key holder and the requested resource. In this scenario, an attacker who obtains or guesses a valid API key can manipulate object identifiers to access data that belongs to other users or organizations. Because the key is treated as the sole authorization factor, the application fails to ensure that the resource being accessed is tied to the key’s associated scope or tenant.

Chi is a lightweight HTTP router for Go that encourages explicit route definitions and parameter extraction. When developers wire API keys into Chi middleware, they often extract the key from headers and use it to fetch tenant or user context. If the subsequent data access does not enforce a relationship between the key’s identity and the object identifier in the route (for example, a user ID or record ID), BOLA emerges. An attacker can change numeric or UUID path parameters to reference other records and the API will return data because the key is accepted as valid.

Consider a Chi route that retrieves a user profile by ID while authenticating via an API key header. The handler resolves the key to a user ID, but then queries the database using the user-supplied ID without confirming it matches the key’s user. This mismatch allows horizontal privilege escalation across accounts sharing the same authentication scheme. In multi-tenant setups where keys are issued per organization, poor scoping can enable vertical escalation if the key has broader permissions than intended, exposing administrative endpoints or sensitive configuration objects.

Real-world attack patterns mirror common OWASP API Top 10 items such as Broken Object Level Authorization. For example, an attacker systematically iterates over identifiers like invoice IDs or document references, observing differences in response status or data content. Without server-side ownership validation, each successful read or update represents a data exposure incident. The presence of API keys does not mitigate this; it simply provides the initial access vector that the BOLA flaw abuses.

Additional risk occurs when keys are embedded in logs, client-side code, or shared environments. If key rotation or scope definition is weak, the attack surface expands. Developers must treat API keys as credentials and enforce strict binding between the key’s metadata and every resource access, ensuring that Chi routes validate tenant or ownership context before returning any data.

Remediation requires tying API key validation to the authorization context of each request, ensuring that object-level IDs are scoped to the key’s owner. In Chi, this is achieved by enriching the request context with tenant or user claims during authentication and then enforcing those claims in handlers and data access layers.

Example of secure middleware that extracts an API key, validates it, and attaches a user ID to the Chi context:

// keyauth.go
package main

import (
	"context"
	"net/http"

	"github.com/go-chi/chi/v5"
	"github.com/go-chi/chi/v5/middleware"
)

type contextKey string

const userIDKey contextKey = "userID"

func apiKeyMiddleware(validKeys map[string]string) func(http.Handler) http.Handler {
	return func(next http.Handler) http.Handler {
		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
			key := r.Header.Get("X-API-Key")
			userID, ok := validKeys[key]
			if !ok {
				http.Error(w, `{"error":"invalid_api_key"}`, http.StatusUnauthorized)
				return
			}
			ctx := context.WithValue(r.Context(), userIDKey, userID)
			next.ServeHTTP(w, r.WithContext(ctx))
		})
	}
}

func profileHandler(db *sql.DB) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		userID := r.Context().Value(userIDKey).(string)
		// Enforce ownership: only fetch records where user_id matches the key’s user
		var name string
		err := db.QueryRow("SELECT name FROM profiles WHERE user_id = $1", userID).Scan(&name)
		if err != nil {
			http.Error(w, `{"error":"not_found"}`, http.StatusNotFound)
			return
		}
		w.Header().Set("Content-Type", "application/json")
		w.Write([]byte(`{"name":"` + name + `"}`))
	}
}

func main() {
	r := chi.NewRouter()
	r.Use(middleware.RequestID)
	r.Use(middleware.Logger)

	validKeys := map[string]string{
		"ak_live_abc123": "user-123",
		"ak_test_xyz789": "user-444",
	}

	r.Use(apiKeyMiddleware(validKeys))
	r.Get("/profile", profileHandler(db))

	http.ListenAndServe(":8080", r)
}

In this pattern, the middleware validates the key and binds it to a user ID stored in context. The handler then uses the user ID from context rather than trusting a route parameter. This prevents BOLA because even if an attacker changes the ID in the URL, the database query will filter by the authenticated user, returning no data or a 404.

For endpoints that reference related resources, such as an invoice ID, always join through the authenticated user or tenant identifier:

// invoice handler with ownership check
func invoiceHandler(db *sql.DB) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		userID := r.Context().Value(userIDKey).(string)
		invoiceID := chi.URLParam(r, "invoiceID")
		var amount int
		err := db.QueryRow(`
			SELECT amount FROM invoices
			WHERE user_id = $1 AND id = $2
		`, userID, invoiceID).Scan(&amount)
		if err != nil {
			http.Error(w, `{"error":"not_allowed"}`, http.StatusForbidden)
			return
		}
		w.Header().Set("Content-Type", "application/json")
		w.Write([]byte(`{"amount":` + strconv.Itoa(amount) + `}`))
	}
}

By embedding the key-derived user ID in every query, you enforce tenant isolation and neutralize BOLA. Rotate keys regularly, limit their scope to least privilege, and avoid exposing keys in URLs or logs. These steps align API key usage with robust object-level authorization in Chi-based services.