RFC 8693 Deep Dive: Token Exchange

Introduction In modern system architectures, particularly in microservices architectures, the following scenarios are incredibly common: Conversion at the API Gateway : You want to exchange a user's access token received from the frontend for a scoped-down token dedicated to each backend microservice. Why exchange it? Because the user's token often has too broad a scope. Following the principle of least privilege, the gateway swaps it for a token containing the "minimum required permissions" and the "appropriate destination (Audience)" before proxying the request to the backend. Service-to-Service Communication : When Service A calls Service B on behalf of a user, it needs to accurately convey "who is calling (Service A)" and "on whose behalf (the User)". Support by Administrators : An administrator needs to temporarily operate the system as a standard user account (Impersonation) to troubleshoot an issue. The traditional OAuth 2.0 (RFC 6749) flows were primarily designed for "a client