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API Authentication Methods Compared

API keys, bearer tokens, JWTs and OAuth — what each is for, their trade-offs, and how to choose.

ConvertAtlas 8 min read Updated May 2026
User App Provider access token

Every API that exposes anything valuable needs to know who is calling. There are several established ways to authenticate API requests, each with different trade-offs in security, complexity and use case. Choosing the right one matters, and mixing them up leads to weak or over-engineered designs. This guide compares the main approaches.

User App Provider access token
Different authentication methods trade off simplicity against flexibility and security.

API keys

An API key is a long secret string the client sends with each request. It is simple to issue and use, which is why it is common for server-to-server integrations and identifying an application. Its weakness is that a key is a long-lived bearer secret — anyone who obtains it has full access until it is revoked — so keys must be kept out of client-side code and rotated when leaked.

Bearer tokens and JWTs

A bearer token is a credential that grants access simply by being presented. JWTs are a popular self-contained form: the token itself carries signed claims about the user, so the server can verify it without a database lookup. This makes JWTs efficient and stateless, but it also means they are hard to revoke before they expire, so they are kept short-lived and paired with refresh tokens.

Try it: JWT DecoderDecode and inspect the header and payload of any JWT.

OAuth 2.0

OAuth is not a single credential but a framework for delegated access — letting a user grant an app limited access to their data on another service without sharing a password. It is the right choice when third parties act on behalf of users, as with "Sign in with" buttons, but it is overkill for a simple internal API where a key would do.

Basic auth

HTTP Basic authentication sends a username and password, Base64-encoded, with each request. Because Base64 is not encryption, it is only safe over HTTPS, and sending credentials on every request is best avoided for anything beyond simple internal tools or quick prototypes.

How to choose

  • Server-to-server or app identity → API key, kept secret and rotated.
  • User sessions in your own app → short-lived JWT or token with refresh.
  • Third-party access on a user’s behalf → OAuth 2.0.
  • Always over HTTPS, always with least-privilege scopes.

The takeaway

There is no single best method — only the right fit for the situation. Match the mechanism to who is calling and what they need, keep secrets short-lived and scoped, and never send credentials over anything but HTTPS.