OAuth 2.0 Client Credentials Flow

A bidirectional authentication protocol where both client and server present X.509 certificates during the TLS handshake. Unlike standard TLS, mTLS cryptographically verifies the client's identity at the transport layer, making it ideal for service mesh architectures where inference APIs must authenticate callers without application-level tokens.

• Eliminates bearer token theft risk by binding identity to a private key
• Commonly deployed with SPIFFE for workload identity in Kubernetes
• Provides defense-in-depth when layered with OAuth 2.0 access tokens

A compact, URL-safe claims format defined by RFC 7519 that encodes a JSON payload with a cryptographic signature. In the Client Credentials Flow, the authorization server issues a JWT as the access token, which the resource server validates locally using the server's public key.

• Stateless validation eliminates token introspection calls on every request
• Claims like sub, iss, exp, and custom scope fields encode authorization context
• Vulnerable to replay attacks unless combined with short expiry windows or DPoP binding

A standard mechanism allowing a resource server to query the authorization server about an access token's current state. Unlike local JWT validation, introspection provides real-time revocation awareness at the cost of added latency per request.

• Returns metadata: active status, scope, client_id, and exp timestamp
• Essential when using opaque tokens that carry no self-contained claims
• Can be cached with short TTLs to balance security and performance in high-throughput inference endpoints

An extension defined in RFC 9449 that cryptographically binds an access token to a specific client instance. The client generates an asymmetric key pair and includes a thumbprint of the public key in a DPoP proof JWT sent alongside each API request.

• Prevents token replay by unauthorized parties who intercept a bearer token
• The resource server verifies the proof's signature and confirms the thumbprint matches the token's binding
• Critical for inference APIs handling sensitive model queries where token exfiltration is a threat vector

An open-source identity framework that assigns cryptographically verifiable identities to every workload in a distributed system. SPIFFE IDs take the form spiffe://trust-domain/path and are embedded in X.509 certificates or JWT tokens.

• Eliminates shared secrets by issuing short-lived, automatically rotated credentials
• Integrates natively with Kubernetes and service meshes like Istio
• Pairs with OAuth 2.0 Client Credentials to provide hardware-attested workload identity before token issuance

A defensive control that restricts the frequency of API calls from a given client identifier. In the Client Credentials Flow, limits are typically enforced per client_id to prevent a compromised service account from exhausting inference resources or executing model extraction attacks.

• Common algorithms: token bucket, sliding window, and leaky bucket
• Should return HTTP 429 with Retry-After headers for graceful backoff
• Combine with anomaly detection to identify query patterns indicative of adversarial probing