KEP-6228: JSON Pointer extraction for Secret and ConfigMap data

[aqeelat]

What type of PR is this?

/kind feature

What this PR does / why we need it:

Adds KEP-6228, proposing RFC 6901 JSON Pointer extraction from Secret/ConfigMap data for both environment variables and projected volume items.

Motivation: Applications frequently need only a small portion of a structured Secret or ConfigMap value. Today they must either receive the entire document (exposing unrelated credentials) or operators must duplicate fields into separate derived Secrets. This KEP enables selecting a JSON subtree directly, closing the least-privilege gap.

Key design decisions:

• Nested jsonPointer: {key, pointer} selector, mutually exclusive with key, so older kubelets see an empty key and fail closed instead of delivering the whole document during version skew.
• RFC 6901 JSON Pointer only (selection-only, not a transform engine). JSONPath/jq/CEL explicitly rejected.
• Number-preserving decode (Decoder.UseNumber), exactly one JSON value (reject trailing data).
• Scalar env var mapping defined: strings decoded, number/bool/null as compact JSON lexical values.
• Feature gate: SecretConfigMapJSONPointer on kube-apiserver + kubelet.

Tracking issue: #6228

Which issue(s) this PR fixes:

Ref #6228

Special notes for your reviewer:

• This is a provisional KEP seeking sig-storage sponsorship.
• One open question remains: non-scalar (object/array) env var targets — reject vs. serialize (see UNRESOLVED block).
• Participating SIGs: sig-node (kubelet env resolution), sig-auth (least-privilege review).

[kubernetes-prow]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: aqeelat
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[linux-foundation-easycla]

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• ✅ login: aqeelat / name: Abdullah Alaqeel (7df5e85)

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