OAuth 2.0 vs API Key — Auth Method Comparison
OAuth 2.0 and API keys are both used to authenticate requests to APIs, but they serve different scenarios. API keys are simple tokens that identify the calling application or user. OAuth 2.0 is a delegation protocol where a user grants a third-party application specific permissions to act on their behalf. The choice depends on whether you need user-level permission delegation or just application-level identification.
Comparison Table
| Aspect | OAuth 2.0 | API Key |
|---|---|---|
| What it authenticates | A user's delegated permissions for a third-party app | A specific client application or service account |
| User involvement | User approves the request and can revoke it | No user interaction required |
| Permission scope | Granular scopes (read:email, write:repos) | Typically all-or-nothing access to an API |
| Expiration | Access tokens expire (minutes to hours); refresh tokens longer | Long-lived or non-expiring by default |
| Revocation | User can revoke per-application at any time | Revocation requires regenerating the key |
| Implementation complexity | Complex; requires authorization server, flows, token exchange | Simple; generate a secret and include it in requests |
| Best for | Third-party integrations requiring user data | Server-to-server, internal APIs, CLIs, automation |
When to Use OAuth 2.0
Use OAuth 2.0 when your API will be accessed by third-party applications on behalf of specific users, and those users need to control what access the application has. OAuth is the right choice for building integrations like "Connect your GitHub account" or "Post to Twitter" — the user authenticates to the provider and grants your app specific permissions, which they can later revoke.
When to Use API Key
Use API keys for server-to-server communication, internal API calls, CLI tools, and scripts where there is no user identity — only application identity. API keys are simpler to implement and understand. For machine-to-machine use cases where OAuth's user delegation complexity adds no value, API keys (potentially combined with short expiry via OAuth's Client Credentials grant) are the pragmatic choice.
Convert Between OAuth 2.0 and API Key
FAQ
- How should I store API keys securely?
- Never commit API keys to source control. Store them in environment variables, a secrets manager (AWS Secrets Manager, HashiCorp Vault), or a .env file excluded from git. Rotate keys periodically and immediately if exposure is suspected. Use scoped keys with minimum required permissions.
- What is OAuth Client Credentials grant?
- Client Credentials is an OAuth 2.0 grant for machine-to-machine authentication with no user involvement. The application authenticates directly with the authorization server using its client ID and secret, receiving an access token. It combines the access control benefits of OAuth (scopes, short-lived tokens) with the simplicity of API keys for service accounts.
- Can I use both OAuth and API keys in the same API?
- Yes and it is common. Many APIs accept OAuth tokens for user-context operations (creating resources as a specific user) and API keys for application-context operations (reading public data, server-to-server calls). GitHub, Stripe, and Slack all support both authentication methods.