Token Exchange at the Gateway

OAuth 2.0 Token Exchange, as defined by RFC 8693, provides a method for services to establish trust by allowing a client to exchange an existing security token for a new one tailored for specific scopes or identity relationships, without re-authenticating. This process is ideally managed at the API gateway, which serves as a centralized point for enforcing security policies and managing token exchanges across services. The API gateway's role in handling token exchanges helps maintain least privilege access, simplify identity complexity for backend services, and ensure privacy by stripping unnecessary claims before forwarding tokens. Kong's implementation, integrated within its OpenID Connect plugin as of version 3.14, performs a series of validation checks to ensure secure token exchanges, addressing new attack surfaces by defining strict trust models. This approach enhances security by treating the API gateway as a security control plane, allowing for consistent, scoped, and trusted tokens regardless of the original authentication method.