Adds opt-in client-credential forwarding for Anthropic passthrough
(single-key/BYOK deployments), plus fixes found in review:
- Startup safeguard now shares one check (server/middleware/auth.rs)
with the live admin PUT /admin/api/config path, closing a bypass
where PROXY_OPEN_RELAY=true alongside 2+ PROXY_API_KEYS entries
slipped past the old startup-only check.
- x-goog-api-key is now recognized as a forwardable credential
(renamed to x-api-key upstream, since Anthropic doesn't understand
that header name), matching validate_auth's precedence.
- Managed (admin-API) backends no longer carry a dead
forward_client_auth field that could never take effect.
- ClientAuthPath forwarding decisions are now double-checked against
live VirtualKeyContext/JwtClaims presence, not just the enum, to
fail closed if the two ever desync.
- Moved from a per-backend BackendConfig field to a global
RuntimeConfig field (like anthropic_thinking_repair), making it
live-toggleable from the admin UI with no restart, and uniform
across every Anthropic-kind backend in a multi-backend deployment.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
whit3rabbit
