OAuth 2.0 token introspection: RFC 7662

Ever had trouble verifying whether an OAuth token presented to your API is still valid?

In OAuth 2.0, tokens are often opaque strings. Random values with no meaningful structure to the resource server. Without a structured token format (like JWT), resource servers and AI agents acting as servers can’t independently validate tokens, leading to potential security risks or constant calls to the authorization server.

RFC 7662 solves this problem by defining a standardized method called token introspection.

What is token introspection, and why use it?

Token introspection allows a protected resource (like your API or an AI agent) to verify the active state and obtain metadata of an OAuth token by querying the authorization server directly. This lets resource servers and AI agents understand if a token is still valid, what scopes it covers, and which user or client it was issued to.

Instead of guessing token validity or assuming indefinite trust, your system can now explicitly confirm a token's status and permissions.

Practical applications of RFC 7662

Token introspection works well in scenarios where resource servers and AI agents require authoritative, real-time verification of tokens. Here are some common real-world use cases:

1. Sensitive data access

APIs or agents dealing with sensitive personal, financial, or healthcare information must ensure tokens are valid at every request.

Example: Medical record APIs or AI-powered assistants verifying tokens for each data access to ensure user consent and token validity.

2. APIs and AI agents with immediate revocation requirements

When immediate revocation of token access is critical, introspection allows servers or agents to enforce revoked tokens instantly.‍

Example: Banking APIs where access must be instantly revoked if a user reports a stolen device.

3. Complex permission management

Systems serving different scopes or fine-grained permissions need real-time scope validation to enforce precise authorization.

Example: A content management API or agent validating tokens before allowing edits, publishes, or deletes.

4. Centralized token management across services and agents

Large-scale applications, microservices, or AI-driven agent architectures benefit from introspection for uniform validation.

Example: An AI agent acting as a resource server validating tokens centrally to maintain consistent, secure authorization.

5. Multi-party integrations for AI agents

AI agents often need to interact with multiple external services on behalf of a user. When receiving tokens from diverse authorization servers, introspection gives the agent a standardized way to validate and understand these tokens without implementing custom logic for each external provider.

Example: An AI sales assistant that coordinates between CRM, calendar apps, and docs.

Why introspection is particularly relevant for AI agents

As more AI agents take on autonomous roles in architectures, they increasingly operate as resource servers, exposing protected APIs or services and receiving OAuth tokens from clients.

• Agents must validate these tokens and understand scopes and permissions before acting.
• When agents can’t access the authorization server’s token store or signing keys (as with opaque tokens), introspection becomes the safest option.
• Agents operating in constrained environments or zero-trust architectures benefit because introspection doesn’t require storing cryptographic keys.

Limitations to keep in mind for AI agents:

• Performance overhead: Each validation requires a network call, which may not suit high-frequency agent operations.
• Authorization server dependency: Agents depend on the authorization server being available.
• Not ideal for agent-to-agent authentication: Most AI agent interactions involve the agent acting as a client rather than a resource server, which makes introspection less relevant in those flows.

The takeaway: introspection is most valuable when your AI agent architecture includes components that need to validate tokens they receive, rather than when agents are primarily making outbound requests.

When not to use introspection

Token introspection may not be ideal if:

• Real-time introspection causes unacceptable latency (e.g., in high-throughput agents).
• Your infrastructure supports structured tokens (like JWT) that can be locally validated.

In these cases, JWT access tokens (RFC 9068) may provide better performance.

Practical example: photo-sharing API

Imagine you’re developing a photo-sharing API (^{https://api.photoshare.com}) used by mobile apps and AI agents to access protected photos. Each app or agent receives an OAuth token after users log in. The resource server must ensure this token is valid before serving sensitive content.

Instead of blindly trusting tokens, your API or AI agent uses token introspection to confirm token validity in real time.

How token introspection works

Step 1: Introspection request

The resource server or agent sends a POST request to the authorization server’s introspection endpoint.

Example request:

Key request parameters:

^token: The OAuth token presented by the client.‍

^{Authentication}: The resource server must authenticate itself (typically with client credentials or a separate access token).

Step 2: Introspection response

The authorization server returns a JSON response indicating whether the token is active, and additional metadata:

What do these fields mean?

• ^active: Indicates token validity (^true or ^false).
• ^client_id: App that requested the token.
• ^username: Resource owner's identifier (human-readable).
• ^scope: Permissions associated with the token.
• ^exp: Expiration timestamp.
• ^iat: Issued-at timestamp.
• ^sub: Subject identifier (typically user ID).
• ^aud: Intended audience (API endpoint).
• ^iss: Authorization server issuing the token.

If the token is inactive (revoked, expired, invalid), the response simply returns:

Inactive token response:

Error handling example

If the resource server's authentication credentials for introspection are invalid or missing, it will get an error response:

Make sure your introspection requests are properly authenticated to avoid such errors.

Security considerations and best practices

Secure introspection endpoint

• Always use HTTPS (TLS) to protect introspection requests and responses.
• Authenticate resource servers strongly (client credentials or dedicated tokens).

Minimize data exposure

• Avoid exposing sensitive data unnecessarily. Return minimal metadata in introspection responses.
• Return ^active:false without detailed errors for inactive or unknown tokens to prevent information leakage.

Caching introspection responses

Cache responses to reduce load and latency but balance carefully:

• Short-lived caching (seconds/minutes) for sensitive APIs.
• No caching if immediate revocation checks are critical.

Avoid token scanning attacks

• Limit introspection endpoint access to trusted resource servers.
• Implement rate-limiting on introspection calls.

Common developer mistakes (and how to avoid them)

Mistake: Not authenticating introspection requests‍

Correct: Always authenticate resource servers:

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Mistake: Overexposing information in responses

Correct: Return minimal details for inactive tokens

Edge cases to consider

• Token revocation can introduce latency. Decide carefully how long your API caches introspection results.
• Be aware that introspection adds overhead: evaluate its impact on high-volume APIs.

Conclusion: empower your APIs and AI agents with RFC 7662

OAuth 2.0 Token Introspection (RFC 7662) provides a standardized, secure, and explicit way to verify OAuth token validity in real time.

For developers building APIs and AI agents, RFC 7662 is a critical tool when your agents:

• Act as resource servers receiving tokens they need to validate.
• Enforce fine-grained scopes and permissions dynamically.
• Operate in environments where storing cryptographic keys isn’t possible.

When your architecture demands real-time, authoritative validation of opaque tokens, especially for AI-driven, multi-party, or agentic systems, RFC 7662 is the right choice.

By adopting RFC 7662, you enable your APIs and agents to make safer authorization decisions, keeping every token check trustworthy and consistent.

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