Hellō This document defines the AAuth authorization protocol for agent-to- resource authorization and identity claim retrieval. The protocol supports four resource access modes — identity-based, resource- managed (two-party), PS-asserted (three-party), and federated (four- party) — with agent governance as an orthogonal layer. It builds on the HTTP Signature Keys specification ([I-D.hardt-httpbis-signature-key]) for HTTP Message Signatures and key discovery.