ClientInfo contract: portable client IP and TLS metadata #475

Summary

ClientInfo contract: portable client IP and TLS metadata with explicit absence, the contract part of #89.

Behavior

One accessor returns the trusted client IP, and one the JA4 fingerprint where a trusted provider supplies it (#283), on every adapter, Fastly and Axum first. JA4 is an EdgeZero abstraction, ctx.ja4(), that each adapter fills from its own source: Fastly from runtime TLS, Cloudflare from Bot Management, Axum from a trusted proxy header such as CloudFront's CloudFront-Viewer-JA4-Fingerprint set by a hop EdgeZero's checked ingress trusts, and Spin never (NotExposed). Trusted Server reads JA4 only through it.

Acceptance criteria

• The same accessors work on each adapter as its part lands, and a JA4 header from an untrusted peer reads as absent

Dependencies

Blocked by:

• PR feat: implement portable outbound HTTP and request lifecycle contracts #275 feat: implement portable outbound HTTP and request lifecycle contracts

Blocks:

• Fastly ClientInfo #90 Fastly ClientInfo
• Cloudflare ClientInfo #91 Cloudflare ClientInfo
• Axum ClientInfo #92 Axum ClientInfo
• Expose JA4 through a standard request interface #283 Expose JA4 through a standard request interface
• EZI-3s Spin ClientInfo, the Spin part of EZI-3 (new in this plan)
• As a developer I want to access client metadata in handlers #89 As a developer I want to access client metadata in handlers
• R2b Integration-branch tag with ClientInfo, JA4 and Axum geo binding (new in this plan)

Related

• Needed by Server-side identity on every adapter trusted-server#1558, server-side identity on every adapter. Planned in wave 2 (MVP: Fastly and Axum); priority P1, size M.
• Requirement EZI-3 in the design.