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Enable validating admission webhook for MCPServer #290

Description

@matzew

Summary

All webhook infrastructure in config/default/kustomization.yaml is commented out. While CEL rules on the CRD handle most validation, the NSA MCP Security Design Considerations (May 2026) recommend defense-in-depth for parameter validation and choosing supported MCP projects.

Proposal

Enable the existing webhook scaffolding and add runtime policy enforcement:

  • Cross-resource validation (e.g., reject images from untrusted registries)
  • Runtime policy enforcement that can be updated without CRD version changes
  • Optional image registry allowlist for spec.source.containerImage.ref

Notes

Full image signature verification (cosign/sigstore) is typically a platform-level concern (e.g., OpenShift image signature verification, policy-controller). A lightweight registry allowlist in the webhook provides defense-in-depth without duplicating platform responsibilities.

Reference: NSA CSI MCP Security Design Considerations - "Validate parameters", "Choose supported MCP projects"
https://www.nsa.gov/Portals/75/documents/Cybersecurity/CSI_MCP_SECURITY.pdf

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