DPoP Adoption & Identity Security Architecture

Demonstrating Proof-of-Possession (DPoP, RFC 9449) secures OAuth 2.0 refresh tokens against interception and replay attacks by cryptographically binding them to a private key held exclusively by the client. In Google's OAuth 2.0 platform, DPoP binds the refresh token at the token endpoint, while access tokens issued for Google APIs are standard Bearer tokens (token_type: "Bearer").

1. Core Cryptographic & Architectural Invariants

When implementing DPoP helpers or upgrading HTTP clients, you MUST adhere to the following strict security invariants:

A. Universal WebCrypto & Runtime Compatibility