Add MCP-Guard — security proxy daemon for MCP servers

[jmolz]

MCP-Guard

Security proxy daemon for MCP servers — adds OAuth 2.1 authentication, PII detection, rate limiting, permission scoping, and audit logging without modifying upstream servers.

Key features:

• Terminate/inspect/re-originate architecture — nothing passes through uninspected
• Fail-closed interceptor pipeline (Auth → Rate Limit → Permissions → Sampling Guard → PII Detect)
• Bidirectional PII scanning with Luhn validation
• Floor-based config merge — personal configs can restrict but never relax base policies

Benchmarks (self-generated, fully reproducible):

• 97% detection across 4,500+ attack scenarios in 10 categories (range: 92.4%–100% per category)
• 0 false positives observed in 10,168 legitimate requests (<0.03% at 95% CI, Rule of Three)
• Tested against own scenario generators, not an independent corpus — methodology doc explains mitigations and known limitations
• Regex-based PII detection — does not catch semantic encoding or cross-field splitting

Links:

• Repository: https://github.com/jmolz/mcp-guard
• npm: @jacobmolz/mcpguard
• License: MIT