What is a bearer token?

A bearer token is a short-lived credential sent in the Authorization: Bearer {token} header. It grants access to a protected resource without requiring the client to prove who they are beyond possessing the token. Bearer tokens are defined in RFC 6750 and are issued by OAuth 2.0 authorization servers after the user grants consent.

An API key is a long-lived static string used to identify and authenticate a client making API requests. It is sent in a header (Authorization: Bearer, X-API-Key, or a custom header) or as a query parameter. API keys are not standardized: each provider defines their format and transmission method.

Which is more secure: bearer token or API key?

Bearer tokens are more secure in practice: they are short-lived (reducing exposure if leaked), scope-limited (limiting blast radius), and user-revocable. API keys are long-lived - a leaked API key grants full access until manually revoked. Both must be kept secret and sent over HTTPS only.

How do I send a bearer token in a request?

Add the Authorization header: Authorization: Bearer YOUR_TOKEN_HERE. In curl: curl -H "Authorization: Bearer YOUR_TOKEN" https://api.example.com/resource. In JavaScript fetch: fetch(url, { headers: { Authorization: "Bearer " + token } }). The "Bearer " prefix (with a space) is required by RFC 6750.

Can API keys replace OAuth for user auth?

No. API keys identify an application or account, not an individual user session. OAuth 2.0 bearer tokens are tied to a specific user who granted consent, carry scopes, and support revocation. If your API needs to act on behalf of a user, you need OAuth. API keys are for machine-to-machine access where there is no user involved.

Last updated: April 14, 2026

Bearer Token vs API Key: Which Should You Use?

Quick Answer

API keys are long-lived static tokens ideal for server-to-server calls and simple integrations. Bearer tokens (OAuth 2.0) are short-lived, scoped, and user-delegated - better for user-facing APIs and third-party integrations. Use API keys for machine-to-machine auth; use bearer tokens for user auth.

Bearer Token vs API Key — Side by Side

Feature	Bearer Token	API Key
Format	JWT or opaque token, sent in Authorization: Bearer header	Opaque string, sent in header or query param
Lifespan	Short-lived (minutes to hours) + refresh tokens	Long-lived (months to permanent)
Scope control	Yes: scopes limit what the token can do	No: API key has full account access
User delegation	Yes: user grants permission to an app	No: tied to the account, not a user session
Revocation	Access token expires; refresh token revocable	Revocable, but long lifespan increases risk window
Best for	User-facing OAuth flows, third-party integrations	Server-to-server, internal services, simple integrations
Standards	OAuth 2.0 (RFC 6749), Bearer Token (RFC 6750)	No formal standard

Verdict

For user-delegated access and third-party integrations, use OAuth 2.0 bearer tokens - they expire automatically, carry scopes, and can be revoked via refresh token. For server-to-server and simple integrations, API keys are easier to implement. Never use API keys for user-facing OAuth flows.

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