What is the critical distinction between Impersonation and Delegation in RFC 8693 Token Exchange?

In RFC 8693 (OAuth 2.0 Token Exchange), impersonation and delegation solve fundamentally different authorization problems across microservice boundaries. In Impersonation, a client or actor acts directly AS the subject, completely assuming the identity and privileges of the subject. The resulting downstream security token contains ONLY the subject identity (sub) with no cryptographically verifiable record that an intermediary performed the action on their behalf. This creates serious non-repudiation and audit compliance risks. In contrast, Delegation explicitly preserves the multi-hop chain of custody: the subject delegates authority to an actor (e.g. Frontend Gateway or Support Admin) to act on their behalf. The exchanged token encapsulates both identities by including an "act" (actor) claim in the JWT. If multiple intermediaries are involved in the call chain (e.g. Gateway -> Order Service -> Billing Engine), the "act" claim is nested recursively (act: { sub: "order-service", act: { sub: "gateway" } }), giving downstream resource servers cryptographic proof of every proxy in the call graph.

How does RFC 8693 prevent cross-service privilege escalation when exchanging subject tokens?

A common vulnerability in distributed microservices is "token replaying" where a downstream service takes a user access token and maliciously reuses it against another internal system. RFC 8693 mitigates this through strict Audience Restriction (aud) and Scope Downscoping during the token exchange flow. When Service A exchanges a subject token at the Authorization Server, it specifies the exact requested audience (resource=https://billing.internal and audience=billing-service) and narrower scopes (scope=read:invoices). The STS (Security Token Service) verifies that Service A is authorized to request delegation for that subject, signs a new JWT with aud restricted solely to the billing service, and strips unused privileges. Even if Service B intercepts this token, it cannot replay it against customer databases or identity services.

How does SCIM v2 (System for Cross-domain Identity Management, RFC 7643/7644) automate identity lifecycles?

SCIM v2 defines a standardized REST and JSON schema for managing user identities, groups, and enterprise extensions across heterogeneous cloud providers (e.g. Okta, Azure AD / Microsoft Entra ID, Google Workspace, AWS IAM Identity Center). Instead of brittle proprietary APIs, identity providers act as SCIM Clients and cloud applications act as SCIM Service Providers. Key operations include: POST /Users (just-in-time provisioning with schema validation), GET /Users?filter=userName eq "alice" and emails[type eq "work"].value pr (standardized filtering), and PATCH /Users/{id} (atomic attribute updates like updating active: false to instantly revoke all enterprise SaaS sessions during employee offboarding without deleting historical records).

What is the structure of SCIM PATCH operations for group memberships and attribute mutation?

RFC 7644 §3.5.2 mandates that SCIM PATCH requests contain an "Operations" array with "op" ("add", "remove", or "replace"), optional "path", and "value". For example, to deactivate a user and change their department simultaneously in a single atomic HTTP request, the client sends: { schemas: ["urn:ietf:params:scim:api:messages:2.0:PatchOp"], Operations: [{ op: "replace", path: "active", value: false }, { op: "replace", path: "urn:ietf:params:scim:schemas:extension:enterprise:2.0:User:department", value: "Former Employees" }] }. For group memberships, adding members without rewriting the entire group uses: { op: "add", path: "members", value: [{ value: "user-id-uuid", display: "Alice Smith" }] }.

OAuth 2.0 Token Exchange (RFC 8693) & Cross-Domain Identity Federation (SCIM v2) Studio

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OAuth 2.0 Token Exchange & SCIM v2 Federation Studio

Simulate RFC 8693 token exchange delegation chains with nested act claims, enforce audience downscoping, and test RFC 7644 SCIM automated user lifecycle provisioning.

Multi-Hop Delegation & Impersonation Simulator

End User / Subject

sub: "alice@corp.com"

➔

Frontend Gateway

actor: "gateway-proxy"

➔

Backend Microservice

actor: "billing-service"

➔

Target Resource

aud: "ledger-db"

Semantics Type

Delegation Depth

Audience Downscoping

RFC 8693 Token Exchange POST Request: grant_type: token-exchange

Exchanged JWT Security Token Payload: act claim nested

OAuth 2.0 Token Exchange & SCIM v2 Federation Studio

Multi-Hop Delegation & Impersonation Simulator

SCIM v2 (RFC 7644) Lifecycle Management & PATCH Engine

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