API Authentication: API Keys vs JWT vs OAuth 2.0

I once shipped an API without authentication. I thought it was a simple internal tool. Two weeks later, a competitor's bot scraped our database at 3 AM. That mistake cost me $1,200 in AWS bills and an awkward talk with my boss.

Authentication is not fun. But if you get it wrong, it will wake you up at 3 AM with an alert.

Here is how to choose between the three main patterns.

  • API Keys These are long random strings. The client sends them with every request. They are simple and fast.

Use them for: • Public APIs like weather or stock data. • Server to server communication. • Prototyping a new idea. • Internal microservices.

  • JWT (JSON Web Tokens) These are signed tokens. They carry user info and permissions inside the token itself. You do not need a database lookup to validate them.

Use them for: • Microservices where each service validates itself. • Mobile apps and single page applications. • High traffic APIs that need to scale.

Warning: Do not put too much data in a JWT. Keep it small. Only include the user ID and roles.

  • OAuth 2.0 This is a protocol for delegation. It lets a user grant access to their data without sharing a password. Think of "Sign in with Google."

Use it for: • Third party integrations. • Systems where users grant specific permissions to different apps. • Enterprise software.

Avoid it for: • Simple internal APIs. • Small teams that need to ship fast.

Quick Decision Guide:

• Public API: Use API Keys. • Internal Microservices: Use API Keys. • Mobile App Backend: Use JWT. • SaaS with user roles: Use JWT. • Third party access: Use OAuth 2.0.

My rule of thumb:

  1. Start with API Keys for internal services.
  2. Add JWT when you need user authentication.
  3. Use OAuth 2.0 only when a client asks for it or you build a platform.

Do not build a perfect system that never ships. Build a secure system that works.

What auth pattern do you use? Tell me in the comments.

Source: https://dev.to/sirmax/api-authentication-in-2026-api-keys-vs-jwt-vs-oauth-20-when-to-use-what-h7c