[TECH DEBT] Upgrade password hashing

[humanauction]

Upgrade password hashing from bcrypt to Argon2

Context

Currently using bcrypt for password hashing (Stage 5 authentication implementation).
Argon2 is the modern standard (OWASP-recommended as of 2023) and provides better resistance to GPU/ASIC attacks through memory-hardness.

Motivation

• Argon2 won the Password Hashing Competition (2015)
• More resistant to hardware-accelerated brute-force attacks
• Configurable memory hardness and parallelism
• Industry best practice for new systems

Proposed Changes

• Replace bcrypt library with libargon2 or argon2-cpp
• Update password hashing in NetMonDaemon login endpoint
• Migrate existing bcrypt hashes to Argon2 (or provide migration script)
• Update sample-config.yaml with Argon2 configuration options (memory cost, time cost, parallelism)
• Update documentation and README with new hashing algorithm
• Add unit tests for Argon2 hashing and verification

Priority

Low (future enhancement after Stage 5 completion)

References

• OWASP Password Storage Cheat Sheet
• Argon2 Specification

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labels: 'security, tech-debt'