API Authentication

Overview

Understand the idea

API authentication confirms who or what is calling an application programming interface. Common mechanisms include API keys, signed requests, OAuth access tokens, mutual TLS certificates, session credentials, and workload identities issued to services.

A strong design validates credentials on every protected request, checks issuer and audience, limits token lifetime, prevents replay, and uses secure transport. Authentication can still fail through leaked keys, weak signature verification, insecure token storage, or unsafe recovery and issuance.

Teams should select mechanisms appropriate to the client type, rotate secrets, separate environments, and log authentication outcomes without recording sensitive credentials. Authentication proves an asserted identity but must be followed by authorization to decide which actions that identity may perform.

What actually happens

API authentication verifies which application, service or user is making a protected request. Crypto-payment integrations often rely on merchant API keys or signed requests so an attacker cannot create invoices or initiate payouts merely by knowing an endpoint URL. The authentication method proves possession of some credential; it does not automatically establish permission to perform every possible action.

The server receives credentials through a specified header or cryptographic signature, validates them over a secure TLS connection and associates the request with a merchant identity. It then performs separate authorization checks for allowed operations, assets, withdrawal destinations and environment. Signatures may incorporate method, path, timestamp, request body and nonce to reduce tampering and replay; exact construction is provider-specific. High-value payout operations should use restrictive key scopes, IP or other network controls where appropriate, short-lived credentials where supported and robust logging that never records raw secrets.

Decisions and failure cases

HTTP 401 and 403 generally signal different kinds of authentication/authorization failures, but provider-specific codes must be read from actual API documentation. Never assume that hiding a key in obfuscated JavaScript makes it secret. Rotating keys and revoking a leaked credential should not require changing unrelated merchant data.

Related concepts

Authentication, Application Programming Interface (API), API Key.

Further reading

Stripe developer documentation: idempotent requests.