Implement Secure PII Vault Persistence for Token Mappings

[007-SARANG]

I am Sarang, a GSoC contributor interested in improving secure data handling in this project.

Currently, PII tokenization exists, but the method responsible for persisting token-to-original mappings (PIIVault.save_mapping) is not implemented. Without secure persistence, tokenization cannot support reliable retrieval or controlled re-identification workflows.

Proposed Improvement:

• Implement secure storage for token-to-original mappings
• Ensure encryption-at-rest for sensitive data
• Introduce basic schema separation for isolation
• Restrict access to authorized internal workflows only

Acceptance Criteria:

• Implement save_mapping with secure storage (e.g., encrypted database or secure backend)
• Ensure sensitive values are encrypted before persistence
• Provide controlled retrieval mechanism for authorized use cases
• Maintain compatibility with existing tokenization flow
• Add tests to verify storage, retrieval, and access control

Note:
This can be further extended into a larger effort around secure PII vault design and lifecycle management.