What's the best authentication strategy for API gateways?

Here's a rundown of authentication strategies for API gateways:

Core approaches

• OAuth 2.0 / OpenID Connect (OIDC) — the standard for most modern API gateways. OAuth 2.0 handles authorization (what a client can access), OIDC layers identity on top (who the user is). This is the default recommendation for anything involving third-party clients, mobile apps, or user-facing APIs.
• JWT (JSON Web Tokens) — commonly used as the token format within OAuth/OIDC flows. The gateway validates the token's signature and claims locally (no round-trip to an auth server needed per request), which keeps latency low. Works well combined with short-lived access tokens + refresh tokens.
• API keys — simplest option, best for server-to-server or partner integrations where you're identifying an application/account rather than an individual user. Not sufficient on its own for anything sensitive — pair with rate limiting, IP allowlisting, or scopes.
• mTLS (mutual TLS) — both client and server present certificates. Common for service-to-service auth inside a mesh, or high-trust B2B integrations, since it authenticates at the transport layer before any request logic runs.
• HMAC request signing — client signs each request with a shared secret; gateway verifies the signature. Used where you need to guarantee the request body hasn't been tampered with in transit (common in webhook and payment APIs).

How to choose

External/public APIs with individual end users → OAuth 2.0 + OIDC, JWT access tokens.

Partner/B2B integrations → API keys or mTLS, often combined with OAuth client-credentials flow.

Internal service-to-service traffic → mTLS via a service mesh, often paired with short-lived JWTs (e.g., SPIFFE/SPIRE-issued identities).

• AI agents / MCP-style consumers — this is a fast-moving 2026 topic: gateways are increasingly issuing scoped, short-lived, agent-specific credentials rather than static API keys, since agents can call many endpoints autonomously and need tighter, auditable scoping.

Implementation best practices

• Authenticate at the gateway, not in each downstream service — centralizes the logic and keeps services focused on business logic. Use short-lived access tokens (minutes to hours) with refresh tokens, rather than long-lived static tokens.

• Scope tokens tightly (least privilege) — a token for reading orders shouldn't also grant write access to billing.

• Validate tokens locally at the gateway when possible (JWT signature verification) rather than calling an auth server synchronously on every request — reduces latency and single points of failure.

• Layer rate limiting and anomaly detection on top of auth — valid credentials being used abnormally (unusual volume, geography, time) is still a signal worth catching. Rotate signing keys and secrets regularly, and support key rotation without downtime (e.g., JWKS endpoints with multiple active keys).

• Log and audit auth failures and token issuance — this is often the first place a breach shows up.

• Bottom line: for most modern API gateway deployments, OAuth 2.0 + OIDC with short-lived JWTs is the baseline recommendation, layered with mTLS for internal service traffic and API keys for simple partner cases.