An API key identifies a calling application. It does not prove which person is behind it. OWASP says not to use API keys for user authentication and warns that OAuth and API keys are not authentication on their own. Use each for what it is good at.
What each one answers
API key: which client program is calling? It is a shared secret held by an application.
User authentication: which human or account is acting? That needs a login, with passwords, multi-factor checks or similar.
OAuth access token: what has this client been allowed to do, possibly on behalf of a user? It is about delegated authorization.
OWASP's broken authentication entry makes both points: understand how each authentication mechanism works, because OAuth and API keys are not authentication on their own, and do not use API keys for user authentication, reserving them for identifying API clients.
What the REST cheat sheet adds
The OWASP REST cheat sheet says to require API keys on protected endpoints, revoke them when clients violate usage terms, and not rely on them alone for sensitive resources. It also says to centralize authentication in an identity provider that issues access tokens.
Comparison
- Identifies: API key: The calling application; OAuth access token: The client, and often a user and scope
- Lifetime: API key: Often long; OAuth access token: Short, with refresh
- Scope: API key: Frequently all or nothing; OAuth access token: Can be narrowed per grant
- Revocation: API key: Delete or rotate the key; OAuth access token: Expire, revoke or stop refresh
- Good for: API key: Usage tracking, quotas, low risk reads; OAuth access token: Acting for a user, finer permissions
Practical rules
- Use keys to identify and meter clients, not to log people in.
- Use short lived tokens issued by an identity provider for user actions.
- Never rely on a key alone for sensitive data or actions.
- Give each key an owner, a scope and an expiry or rotation date.
- Issue separate keys per client and environment so you can revoke one without breaking others.
- Put keys in headers, not URLs.
What to do when a key leaks
Rotate first, investigate second. Replace the key, check logs for use between leak and rotation, and find how it leaked. See how to rotate leaked API keys and designing a key that can be found when it leaks.
Mixing the two
A common and sound design: the key identifies the integration and sets quotas, while an access token proves the user and sets scope. A request carries both, and the server checks each separately.
Quick check
Is an API key enough for a public read only endpoint?
It can be, for metering and abuse control. The cheat sheet's warning is about sensitive resources.
Does having OAuth mean users are authenticated?
OAuth is an authorization framework. User authentication happens at the identity provider, and the API must still validate the resulting token.
Safeguard's free scan at gold.safeguard.sh/scan and its dependency scanning help you find known issues in your auth libraries, and its policies can enforce rotation checks in pipelines.
Sources
Last reviewed: 19 October 2026.
