API Authentication BasicsAPI Authentication Basics

Introduction

API authentication is how the server knows who is calling. We'll cover the main approaches: API keys, Bearer tokens, and OAuth-style flows, and when to use them. Choosing the right method (API key, Bearer token, or OAuth) depends on who the client is (your app, another service, or an end user) and whether you want to delegate identity to a provider. Below: how to implement and document them securely.

What Is API Authentication Basics

Authentication answers “who is this?” For APIs, the client sends something the server can verify: an API key in a header, a Bearer token (e.g. JWT), or proof from an OAuth flow. The server checks it and then may apply authorization (“is this user allowed to do this?”). Auth is required for protected endpoints; public endpoints may allow anonymous access.

Why It Matters

Without auth, anyone could call your API. With it, you can rate-limit per user, log who did what, and enforce permissions. Choosing the right method (key vs token vs OAuth) depends on who the client is (your app, another service, or an end user) and how much you want to delegate to an identity provider.

How to Calculate It

Real-Life Example

Your mobile app: user logs in; your backend returns a JWT. The app sends it as Authorization: Bearer <jwt> on every request. Your API verifies the JWT and reads user id. For a partner integration, you issue an API key; the partner sends it in a header. You look up the key and map it to a project or account for rate limiting and billing.

Common Mistakes

Sending API keys or tokens in the URL (they get logged). Not using HTTPS so tokens are sent in the clear. Not validating tokens on every request. Storing tokens insecurely on the client. Using the same key for different environments or purposes.

Practical Tips

• Use HTTPS for all authenticated requests.
• Prefer Bearer tokens or standard headers; avoid custom auth in the URL.
• Validate the token (signature, expiry, issuer) on every protected request.
• Issue different keys or tokens per environment and per client when possible.
• Document how to obtain and send credentials in your API docs.

FAQs

Conclusion

API auth identifies the caller via keys, Bearer tokens, or OAuth. Use HTTPS, validate on every request, and store credentials securely. Document the flow for your clients.