Implement Phase 3 of Custom DNS Provider Plugin Support with comprehensive
security controls for external plugin loading.
Add CHARON_PLUGIN_SIGNATURES env var for SHA-256 signature allowlisting
Support permissive (unset), strict ({}), and allowlist modes
Add directory permission verification (reject world-writable)
Configure container with non-root user and read-only plugin mount option
Add 22+ security tests for permissions, signatures, and allowlist logic
Create plugin-security.md operator documentation
Security controls:
Signature verification with sha256: prefix requirement
World-writable directory rejection
Non-root container execution (charon user UID 1000)
Read-only mount support for production deployments
Documented TOCTOU mitigation with atomic deployment workflow
Phase 1 of Custom DNS Provider Plugin Support: the /api/v1/dns-providers/types
endpoint now returns types dynamically from the dnsprovider.Global() registry
instead of a hardcoded list.
Backend handler queries registry for all provider types, metadata, and fields
Response includes is_built_in flag to distinguish plugins from built-ins
Frontend types updated with DNSProviderField interface and new response shape
Fixed flaky WAF exclusion test (isolated file-based SQLite DB)
Updated operator docs for registry-driven discovery and plugin installation
Refs: #461
