Every API you call needs to know who is calling before it answers, and every API you build needs a way to reject callers it does not know. The wrong choice either leaks access or buries your users in setup friction. Here are the five API authentication methods you will actually meet, what each is good for, and how to choose.
What are the main API authentication methods?
The five methods in common use are API keys, OAuth 2.0 access tokens, JWT bearer tokens, HTTP Basic authentication, and session cookies. API keys identify an application, OAuth delegates a user's permission to an application, JWTs carry signed identity claims, Basic sends credentials directly, and sessions track a logged-in browser.
API keys
An API key is a long random string issued once and sent with every request, either as a query parameter or a header. It answers "which account is calling" and nothing more. Keys are the standard for server-to-server data APIs because setup is one copy-paste.
Abstract's APIs work this way: you pass ?api_key=YOUR_KEY with each request, and the key ties usage to your account and plan. The trade-off with any key: it does not expire on its own, so treat it like a password. Keep it server-side, out of client code and out of version control, and rotate it if it leaks.
OAuth 2.0
OAuth 2.0 answers a different question: "may this app act on this user's behalf?" The user approves once, your app receives a short-lived access token plus a refresh token, and the API accepts the access token until it expires. This is the method behind "Sign in with Google" and every integration that touches someone else's account data.
Choose OAuth when your product needs to read or write data a user owns on another platform. The cost is real: redirect flows, token storage, refresh logic, and scope management. For a data lookup API with no user-owned resources, OAuth adds friction without adding safety.
JWT bearer tokens
A JSON Web Token is a signed package of claims (user ID, role, expiry) that the server can verify without a database lookup. The client sends it as Authorization: Bearer <token> on each request. JWTs shine in microservice architectures and first-party mobile or single-page apps, because any service holding the public key can verify the caller locally.
Two rules keep JWTs safe: keep lifetimes short, since a stolen token works until it expires, and never put secrets in the payload, because anyone holding the token can decode it. Signing proves integrity, not confidentiality.
Basic authentication and sessions
HTTP Basic sends a username and password with every request, base64-encoded but not encrypted. Over HTTPS it is acceptable for internal tools and quick prototypes; for anything public it puts long-lived credentials on the wire constantly, so most APIs have moved past it.
Session cookies belong to browsers: the user logs in, the server stores a session and sets a cookie, and the browser replays it automatically. Sessions are right for your own web app's frontend talking to its backend, and wrong for third-party or server-to-server APIs, where there is no browser to manage cookies and CSRF protection.
How to choose
- Server-to-server data lookups (validation, enrichment, geolocation): API keys. One credential, no expiry dance.
- Acting on a user's data at another service: OAuth 2.0. Nothing else grants delegated, revocable, scoped access.
- Your own distributed services or SPA/mobile backend: JWT bearer tokens with short lifetimes.
- Browser frontend of your own web app: session cookies.
- Internal prototype behind a VPN: Basic auth is fine until it ships.
Whichever method you pick, enforce HTTPS everywhere, apply rate limits per credential, and log authentication failures; the broader checklist lives in API security.
Frequently Asked Questions
What is the most common API authentication method?
API keys, by a wide margin, for machine-to-machine APIs. They are simple to issue, simple to send, and tie every request to an account for quota and billing. OAuth 2.0 dominates wherever apps act on a user's behalf.
Is an API key the same as a password?
Functionally yes: anyone holding the key can spend your quota. The difference is scope; a key unlocks one API surface rather than a whole account, and you can usually rotate it without changing your login.
When should I use OAuth instead of an API key?
Use OAuth when the data belongs to your end user on another platform and they must consent. Use an API key when your server calls a data service on its own behalf, with no third-party user in the loop.
Are JWTs more secure than API keys?
They solve different problems. JWTs expire quickly and carry claims, which limits damage from theft; API keys are long-lived but easier to manage. A leaked key with no expiry is riskier than a leaked 15-minute JWT.
Can I combine authentication methods?
Yes, and most real systems do: OAuth or sessions authenticate users at the edge, while services exchange JWTs internally and call external data APIs with keys. Each hop uses the method that fits it.
Where should I store API keys?
In environment variables or a secrets manager on the server, never in frontend code, mobile binaries, or a repository. If a key must reach a browser, proxy the request through your backend instead.
