API Authentication Demystified: API Keys vs Bearer Tokens vs OAuth 2.0
Learn how to secure web APIs using API keys, JWT bearer tokens, and OAuth 2.0 PKCE workflows with complete authentication header examples.
Securing an http api is paramount. Without robust authentication, endpoints can be abused, databases compromised, and server bills inflated. There are three industry-standard authentication patterns for modern web APIs.
1. API Keys (Machine-to-Machine)
The simplest scheme: a unique secret string passed in a request header or query parameter.
GET /api/v1/analytics HTTP/1.1 X-API-Key: cf_live_8923b49f98a7201c
2. JWT Bearer Tokens (Stateless Sessions)
JSON Web Tokens encode user claims, expiration time, and cryptographic signatures in a compact base64 format.
GET /api/v1/user/settings HTTP/1.1 Authorization: Bearer eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJzdWIiOiIxMjM0NTY3ODkwIiwibmFtZSI6IkpvaG4gRG9lIn0...
3. OAuth 2.0 & OpenID Connect (Delegated Authorization)
Used when third-party applications need limited access to user data (like signing in with Google or GitHub) without ever seeing the user's password.