Token Introspection

The introspection endpoint returns a boolean active claim indicating whether the token is currently valid. Unlike local JWT validation, this queries the authorization server directly, catching revocations, expirations, and policy changes in real-time.

• True: Token is valid, not expired, and not revoked
• False: Token is invalid, expired, revoked, or malformed
• Eliminates the revocation window problem inherent in stateless token validation

Upon successful introspection, the authorization server returns a JSON payload containing the token's metadata claims. This includes scope, client ID, expiration, and custom attributes, allowing the resource server to make fine-grained authorization decisions.

• scope: Space-separated list of granted scopes
• exp: Token expiration timestamp (Unix epoch)
• sub: Subject identifier for the authenticated principal
• client_id: The OAuth 2.0 client that obtained the token
• Custom claims for attribute-based access control (ABAC) policies

Introspection enables Continuous Access Evaluation Protocol (CAEP) patterns by allowing resource servers to validate tokens on every request or at defined intervals. If a user's session is terminated or device posture changes, the introspection response immediately reflects the revocation.

• Supports session-bound tokens that become invalid when the TLS connection drops
• Enables just-in-time authorization by re-evaluating policies at query time
• Critical for AI agent access where long-lived tokens pose exfiltration risks

The introspection endpoint is an OAuth 2.0 protected resource itself. The resource server must authenticate to the authorization server, typically using client credentials or mutual TLS (mTLS) to prevent unauthorized token probing.

• HTTP Basic Auth: Client ID and secret over TLS
• Bearer token: A separate access token with introspection scope
• mTLS: X.509 certificate-based mutual authentication
• Prevents token scanning attacks by unauthorized parties

The introspection endpoint accepts a token_type_hint parameter to optimize lookup. While optional, providing the hint reduces latency by directing the authorization server to the correct token store.

• access_token: OAuth 2.0 access token for API authorization
• refresh_token: Long-lived token used to obtain new access tokens
• id_token: OpenID Connect identity token containing user claims
• If the hint is incorrect, the server must still perform the lookup across all token types

Introspection requests expose sensitive token data in transit. Deployments must enforce TLS 1.3 with strong cipher suites and consider network segmentation to isolate the introspection channel from public-facing infrastructure.

• Use micro-segmentation to restrict introspection traffic to authorized resource servers
• Deploy API gateways to rate-limit introspection calls and prevent abuse
• Implement mutual TLS (mTLS) for bidirectional certificate validation
• Log all introspection requests to immutable audit logs for compliance

The architectural component that intercepts access requests to protected resources and enforces authorization decisions. In an AI data pipeline, the PEP sits in front of the resource server—often an API gateway or reverse proxy—and calls the token introspection endpoint on the Policy Decision Point (PDP). The PEP translates the introspection response's active boolean and scope claims into a binary allow/deny decision, blocking expired or revoked AI agent tokens before any data is served.

A security practice where elevated access privileges are granted dynamically for a limited duration only when needed. Applied to AI retrieval systems, JIT eliminates standing access by requiring an agent to request a scoped, short-lived token immediately before querying a sensitive data store. Token introspection validates that the grant window—often measured in seconds—has not elapsed, minimizing the attack surface for compromised AI service accounts that might otherwise hold long-lived credentials.

A protocol where both client and server authenticate each other using X.509 certificates. In a zero-trust AI access architecture, mTLS ensures that the resource server's token introspection request to the authorization server occurs over a mutually authenticated channel. This prevents man-in-the-middle attacks on the introspection endpoint itself and guarantees that only verified AI services with valid client certificates can establish connections to enterprise data stores in the first place.