HTTP Compliance Authorization Protocol (HCAP)

This document specifies the HTTP Compliance Authorization Protocol (HCAP), an extension to the HTTP authentication framework that allows resource providers to require demonstrable evidence of caller compliance with declared policies before granting access to protected resources. Callers obtain signed compliance credentials from a compliance registry by presenting evidence of their controls. Credentials are conveyed at the HTTP layer and verified offline by the provider. HCAP operates alongside existing authentication schemes (OAuth 2.0, mTLS) and does not replace identity authentication. It addresses the distinct question of "does the caller meet declared policy requirements" rather than "who is the caller".