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To let an agent act for a user safely, keep the user as the token’s subject, identify the agent as its actor, grant only the necessary resource and operations, and have the resource server check each request against that grant. OAuth token introspection can reveal a token’s current status and authorization context; it does not, by itself, authorize a requested operation.
How can an agent act on a user’s behalf?
Model three things separately: the user the action is on behalf of, the agent making the request, and the resource and operation the request targets. This makes it possible to apply policy to the user’s rights and the agent’s delegated authority without losing track of who actually acted.
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OAuth token exchange provides a standard framework for requesting a token based on an existing token. In a delegation scenario, the subject_token represents the party on whose behalf a token is requested, while the actor_token represents the party receiving delegated rights. The authorization server decides, according to its policy and configuration, whether to issue a token that represents both identities and what rights it contains. See RFC 8693, OAuth 2.0 Token Exchange.
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Keep delegation distinct from impersonation
With delegation, the agent remains identifiable as the actor and has delegated rights. With impersonation, the policy treats the actor as indistinguishable from the represented user within the relevant rights context. These are different identity semantics, not interchangeable labels. Choose delegation when audit and policy decisions need to distinguish the user from the agent; use impersonation only when the system intentionally treats the actor as the user.
#1 Best Overall
How do you limit an agent to specific actions?
Define authorization in terms of both the intended resource and the permitted operation. A broad grant such as a general read scope may be insufficient when an API needs to distinguish which record, account, or transaction an agent may access, or which action it may perform there.
OAuth scopes can express broad permissions. OAuth Rich Authorization Requests (RAR) add a way for clients to express fine-grained authorization requirements in JSON using authorization_details. The field meanings and schema are specific to the API; RFC 9396 does not define one universal set of detail fields for all services. See RFC 9396, OAuth 2.0 Rich Authorization Requests.
| Authorization approach | Useful when | Important boundary |
|---|---|---|
| OAuth scope | The API can express the needed permissions as broader categories of access. | The scope vocabulary and its relationship to resources or actions must be understood by the client, authorization server, and resource server. |
authorization_details |
The API needs to express requirements more specifically, such as a particular resource or an operation with transaction details. | The API defines the meaning of its fields; the format does not create universal semantics or enforce the grant on its own. |
RFC 9700, the OAuth 2.0 Security Best Current Practice published in January 2025, recommends associating access tokens with relevant resources and actions. The resource server should check on every request that the token is intended for the target resource and covers the requested action. Clients and authorization servers may use scopes and authorization_details to determine resources or actions. See RFC 9700.
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Define resource identifiers and allowed operation names so each participating component can interpret them consistently. The resource server must enforce the granted details for the actual request; it should not infer permission merely because a client originally asked for that detail.
How can a resource server check what an access token allows?
Token introspection lets a protected resource query the authorization server about a token’s current state and metadata. Under RFC 7662, an introspection response can indicate whether the token is active, describe its access rights, and provide context such as who authorized it and which client received it. What counts as “active” is authorization-server dependent; the RFC’s common definition includes a token that was issued by that server, has not expired or been revoked, and is valid for the resource making the query. See RFC 7662, OAuth 2.0 Token Introspection.
An active response is not proof that the token permits every operation. The resource server still has to compare the token’s relevant authorization context with the resource and action in the incoming request. Introspection supplies information for that decision; it does not replace the decision.
Introspection or locally verifiable token content?
Introspection gives the resource server an authorization-server query path for token status and metadata, regardless of whether metadata is also carried in the token. Locally verifiable token content is another possible way for a deployment to make token information available. The cited standards do not establish a universal choice, performance figures, or a required caching strategy; those are deployment decisions.
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| Consideration | Introspection query | Locally verifiable token content |
|---|---|---|
| How the resource server gets context | Queries the authorization server’s introspection endpoint. | Uses token content it can verify locally. |
| What the cited guidance establishes | RFC 7662 defines the query and response approach for token status and metadata. | The source set does not specify a token format or prescribe this approach. |
| What remains deployment-specific | Any caching behavior and how introspection results fit the service’s decision process. | Token format, validation details, and how current authorization state is represented. |
Protect the introspection endpoint: RFC 7662 requires authorization to access it and specifies TLS 1.2 support and certificate checking when TLS is used. Introspection receives tokens and returns information that can influence authorization decisions, so exposure of the endpoint or its responses matters.
Best Value
How should a delegated authorization flow work?
- Identify the user and agent. Establish which user is represented and which agent is acting. Preserve both identities when the policy calls for delegation.
- Define the requested grant. Specify the resource and operations the agent needs. Use scopes where broad categories are adequate; use API-defined
authorization_detailswhen finer distinctions are required. - Request delegated credentials. If using token exchange, identify the subject and actor using the applicable token-exchange parameters. The authorization server’s policy determines whether it issues a token and what authorization context it carries.
- Protect authorization details in transit. Details that pass through a user agent can be modified or swapped. RFC 9396 says clients must protect them against tampering and swapping when integrity matters; signed request objects or a request URI that references a request object are possible mechanisms.
- Check every resource request. The resource server verifies that the token is intended for that resource and that its granted context covers the requested operation. If it uses introspection, the response informs this check but does not substitute for it.
- Enforce the grant that was issued. Resource servers should act on the granted authorization details, not on a client’s original request alone. The authorization server should make the granted details clear.
What these OAuth standards do—and do not—decide
RFC 7662 (October 2015) defines token introspection; RFC 8693 (January 2020) defines token exchange; RFC 9396 (May 2023) defines Rich Authorization Requests; and RFC 9700 (January 2025) provides OAuth 2.0 security best-current-practice guidance. These IETF documents provide protocol mechanisms and security guidance, not a turnkey policy for authorizing every kind of agent.
- Your authorization server’s issuance policy determines whether token exchange results in a delegated token and what it represents.
- Your API defines the meaning of its
authorization_detailsfields and the precision of its resource and operation identifiers. - Your resource server must enforce the granted context for each requested resource and action.
The cited specifications are international protocol documents; they do not establish jurisdiction-specific legal requirements.
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