API Security Checklist

Authenticate and authorise

Two distinct questions sit at the front of any secure integration. Authentication establishes who is making a request; authorisation decides what that identity is permitted to do. Get them in the right order: verify identity first, then check permission for the specific action, and never assume a valid identity may do everything.

Use the API's intended mechanism rather than improvising. Where the platform offers a standards-based flow such as OpenID Connect, prefer it over hand-rolled schemes. Our developer documentation describes the supported authentication and the scopes that govern what each credential may access.

Guard your secrets

Credentials — API keys, client secrets, tokens — are the keys to your access, and most breaches involve a leaked one. Never commit them to source control, embed them in client-side code, or paste them into logs. Keep them in a secret manager or environment configuration, separate from the code that uses them.

# secrets come from the environment, never the repo
api_key = env('MERION_API_KEY')
# never: api_key = 'live_8f3a...'   # leaked forever

Rotate secrets periodically and immediately on any suspected exposure, and scope each credential to the least it needs so a leak is contained.

Validate, encrypt, least-privilege

Three habits cover much of the rest. Validate every input at the boundary so malformed or hostile data is rejected before it spreads. Encrypt data in transit with current TLS and sensitive data at rest. Apply least privilege everywhere — each credential, service, and person gets only the access it genuinely requires, no more.

These reinforce one another. Validation limits what an attacker can inject, encryption limits what they can read if they get in, and least privilege limits what any single compromised component can reach. Treating the three as a single layered defence — rather than picking one and hoping it suffices — is what makes an integration genuinely hard to compromise, since an attacker now has to defeat all three rather than any one.

Handle errors without leaking

Error handling is a quiet security boundary. Detailed errors — stack traces, internal identifiers, database messages — help attackers map your system, so return generic messages to clients while logging the detail privately for yourself. The caller learns enough to act; the attacker learns nothing useful about your internals.

Take the same care with what your responses and logs reveal: leaking a token, a personal detail, or an internal path through an error message undoes other controls. A reference identifier in the response, with the full detail kept in your own logs, gives you debuggability without disclosure.

Make it a habit

Security is not a box ticked once at launch. Dependencies gain vulnerabilities, scopes drift wider than intended, and secrets quietly age past their rotation date. Treat this checklist as a recurring review — revisit it on a schedule and whenever your integration changes materially — so controls that were sound at launch stay sound over time.

Keep it proportionate and practical: a short, regular pass over authentication, secrets, validation, transport, least privilege, and error handling catches most drift cheaply. Pair it with dependency management so your supply chain is part of the same routine rather than an afterthought.