How to Secure a REST API: A Practical Checklist
An API is often the most exposed part of a modern application — it's designed to accept requests from the outside world by definition, which means it's also the most direct path an attacker has to your data and your business logic. Securing one properly isn't a single feature; it's a checklist of separate concerns, each one worth going through deliberately.
Authentication: proving who's making the request
Every request to a protected endpoint needs a reliable way to identify who's making it. Common, solid approaches include API keys for service-to-service communication and token-based authentication (like OAuth 2.0 or JWTs) for user-facing applications. The specific mechanism matters less than getting the basics right: tokens should expire, they should be transmitted only over encrypted connections, and they should never appear in a URL, where they're far more likely to end up logged somewhere insecure.
Authorization: checking what they're allowed to do
Authentication answers "who are you." Authorization answers "what are you allowed to do," and it's a separate check that has to happen on every single request — not just once at login. A very common, damaging mistake: an API correctly checks that a request has a valid token, but never verifies that the specific resource being requested actually belongs to that user. This is how one user ends up able to view or edit another user's data just by changing an ID in the request — a version of broken access control, one of the most common findings in real-world security reviews.
Rate limiting: protecting against abuse and overload
Without rate limiting, a single client — malicious or just badly configured — can hammer your API with requests, either to brute-force something like a login endpoint or simply to overload your infrastructure. Practical rate limiting means setting sensible request limits per user or per API key, returning a clear response when a client hits the limit, and applying stricter limits to sensitive endpoints like login and password reset than to routine read requests.
Input validation: never trust what arrives
Every field in every request should be validated against what's actually expected — type, length, format, allowed range — before it's used anywhere in your application logic. This is the same principle that prevents SQL injection, but it applies far more broadly: malformed or unexpected input is behind a large share of real application vulnerabilities, well beyond database queries specifically.
Transport security: encrypt everything, no exceptions
Every request and response should travel over HTTPS, with no unencrypted fallback available at all, even for endpoints that feel low-risk. Modern tooling (like Let's Encrypt) makes this close to free to set up properly, so there's rarely a good excuse for skipping it anywhere in your API surface.
Sensible error messages
Detailed error messages are genuinely helpful during development and genuinely dangerous in production. An error that reveals internal file paths, a database version, or a full stack trace hands an attacker a head start on finding a real weakness. Production error responses should be informative enough to be usable, and nothing more.
Logging and monitoring
You need a real record of who accessed what, and when — not to slow anything down, but so that if something does go wrong, there's an actual trail to investigate rather than a shrug. Watching for unusual patterns, like one account suddenly making an unusually high volume of requests, can catch an active attack early, before it turns into a real incident.
A checklist worth running against your own API
- Does every endpoint require authentication, except the ones deliberately meant to be public?
- Does every request check that the user is authorized for that specific resource, not just logged in generally?
- Is rate limiting in place, especially on login, password reset, and other sensitive endpoints?
- Is every input validated before use, not just the ones that seemed obviously risky?
- Is HTTPS enforced everywhere, with no exceptions?
- Do production error responses avoid leaking internal implementation details?
- Is there enough logging to actually investigate an incident after the fact?
Working through this list carefully — endpoint by endpoint, not just in the abstract — is exactly the kind of hands-on application security review Burncode runs for clients, alongside infrastructure hardening and getting ready for a real compliance audit.