Conditional Access for HTTP

This document introduces conditional access to resources based on pricing constraints signaled via request and response headers. An origin states the conditions for serving a resource, and a client states the constraints under which it will accept it. This specification applies this conditional access approach using standard HTTP request and response semantics while staying interoperable with intermediaries. It introduces a Pricing response header field that communicates current pricing terms and an If-Price- LTE request header field that allows a client to declare a maximum acceptable price. When a request is served under such conditions, the response includes a Response-Id header identifying the served response context. This identifier can be used for reconciliation, auditing, and downstream usage reporting. This specification defines access condition signaling only. Accounting and usage reporting may be implemented using a companion protocol such as usage-log.