API Key vs OAuth 2.0 Access Token

What is the difference between an API Key and an OAuth 2.0 Access Token? When would you choose one over the other in a secure system?

The API Key

An API Key is a simple string of characters (like a password) that identifies who is calling the system.

How it works You give the key to a developer. Every time their application talks to your server, it sends that key. Analogy It's like a gym membership card. It tells the gym who you are, and as long as the card is valid, you can walk in. Security Level Low to Medium. If someone steals your card, they can pretend to be you until you cancel it.

OAuth 2.0 Token

An OAuth 2.0 Access Token is much more sophisticated. It doesn't just say who you are; it says exactly what you are allowed to do and for how long.

How it works Instead of one permanent key, the user goes through a "login" process. The system then issues a temporary token that might expire in an hour.

Analogy It's like a hotel key card. It only opens your room (not the whole hotel), and it stops working automatically the moment you check out.

Security Level High. Even if someone steals it, the token is only useful for a short time and for very specific tasks.

Choose an API Key when...

• You are building a simple service (like a weather app) where you just need to track how many people are using your data.
• The data isn't "private" to a specific user (public maps, currency exchange rates).
• You are doing Server-to-Server communication where you trust both sides completely.

Choose OAuth 2.0 when...

• User Privacy is involved: If an app needs to access a user's private Google Photos or Spotify playlists, you must use OAuth.
• Security is a priority: You want the ability to kick a specific user out without changing the keys for everyone else.
• Third-party apps: You want to let another app use your data without giving that app your actual password.