API Authentication in 2026: JWT vs OAuth2 vs API Keys (With Python Examples)

Every API you build needs authentication. But which method should you use? I've implemented all three in production systems. Here's when to use each — with working Python code. Quick Decision Tree Is it a public API (no user data)? → API Key Does it need user-specific data? → OAuth2 Is it internal/microservices? → JWT Is it server-to-server? → API Key or JWT 1. API Keys — The Simple Choice Use when: Public APIs, rate limiting, usage tracking. from fastapi import FastAPI , Header , HTTPException import secrets app = FastAPI () # In production: store in database VALID_KEYS = { secrets . token_hex ( 32 ): { ' user ' : ' client_1 ' , ' tier ' : ' free ' }, } @app.get ( ' /api/data ' ) async def get_data ( x_api_key : str = Header (...)): if x_api_key not in VALID_KEYS : raise HTTPException ( 401 , ' Invalid API key ' ) client = VALID_KEYS [ x_api_key ] return { ' data ' : ' here ' , ' client ' : client [ ' user ' ]} Pros: Dead simple. Works everywhere. Easy to rotate. Cons: No user identit