P1-mcp-auth: OAuth 2.1/OIDC short-lived scoped tokens for MCP boundary

[omarespejel]

Summary

Harden MCP server authentication with modern token-based identity and scoped authorization.

Problem

HMAC/mTLS replay controls are necessary but not sufficient for multi-tenant/third-party client usage.

Scope

• Add OAuth 2.1/OIDC validation path for MCP entrypoints.
• Enforce short-lived access tokens and audience checks.
• Enforce scope-to-tool mapping (tool:*, read:*, write:*).
• Add token subject binding to request trace IDs and audit logs.
• Keep existing proxy controls (P0-proxy: HMAC + mTLS + nonce replay protection (Redis TTL) #219) as defense-in-depth.

Acceptance Criteria

• Unscoped token cannot invoke privileged tools
• Expired token is rejected deterministically
• Scope checks are visible in structured audit logs
• Docs include deployment profile (issuer/jwks/audience)

Dependencies

• P0-proxy: HMAC + mTLS + nonce replay protection (Redis TTL) #219 proxy auth + replay protections
• P1-observability: correlated audit logs across MCP, signer, and tx execution #224 correlated audit logs
• P2-auth: implement SISNA (Starknet Sign-In With Agent) nonce/verify/receipt package #225 SISNA auth package

[omarespejel]

Launch-profile update (2026-03-05): this issue is deferred from the no-backend/self-custodial launch gate and is now tracked under #325.\n\nStatus: remains open and important for managed-backend mode, but non-blocking for #273.

[omarespejel]

Milestone update (2026-03-06): moved out of Milestone 2 ("Security Proof & Attestation v1") as non-blocking for the no-backend/self-custodial launch profile tracked in #273. This issue remains open and will be tracked as managed-backend-later work.