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Stephan Renatus
13e9488921
Wrapping projects can now attach custom metadata to Data API requests
and have evaluation produce response metadata.
Introduce two distinct metadata paths:
- Request (incoming) metadata: parsed from extra top-level keys in the request
body, made available to builtins via `BuiltinContext.RequestMetadata`.
Logged in the decision log under `Custom["request_metadata"]`.
- Response (outgoing) metadata: a separate map (`BuiltinContext.ResponseMetadata`)
that builtins can populate during evaluation. Only included in the
API response and decision log (`Custom["response_metadata"]`)
if non-empty.
In vanilla OPA, no builtins write response metadata, so responses are
unchanged. The request metadata map is only allocated when the request
carries extra fields; the outgoing map is one empty map per request.
To avoid conflicts with future OPA top-level keys, callers should use a
namespaced key: `{"input": {...}, "com.example.opa/md": {...}}`.
```mermaid
flowchart LR
req["POST /v1/data\n{input, com.example.opa/md}"]
parse["readInputPostV1"]
eval["topdown eval"]
resp["API response"]
dl["decision log"]
req --> parse
parse -- "reqMetadata" --> eval
parse -- "reqMetadata" --> dl
eval -- "respMetadata\n(if non-empty)" --> resp
eval -- "respMetadata\n(if non-empty)" --> dl
eval -. "BuiltinContext\n.RequestMetadata\n.ResponseMetadata" .-> eval
```
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Signed-off-by: Stephan Renatus <stephan.renatus@gmail.com>