MCP Server Auth: The API Is the Real Boundary

A single shared API key is fine right up until a second person uses it. intent-brain — the system, repo qmd-team-intent-kb , renamed to the intent-brain plugin v0.4.0 this day — is a team knowledge base. A Fastify HTTP API sits over a governed memory corpus. In front of that API is an MCP server named teamkb , so a teammate doesn't open a dashboard or learn an endpoint. They ask in Claude Code and get a cited answer back with qmd:// citations. That's the whole pitch: institutional memory you query in the same place you write code. Up to this day it authenticated with one shared TEAMKB_API_KEY . The shared key has two failures that only show up once the tool has more than one user. First, every request looks identical, so the audit log can't say who asked. Second, revoking one person means rotating the key for everyone — there's no per-person handle to drop. Both are structural, not bugs you patch. You fix them by giving each person their own credential. The work closed that gap with three things, in this order: per-user tokens (identity), a server-side write gate (authorization), and a per-read access log (audit). The through-line: the API is the real boundary. The MCP client-side tool gate is UX, not security. And the per-read access log stays separate from the governance audit trail — separate log, not no log. Identity: per-user tokens replace the shared key apps/api/src/auth/token-registry.ts . Each token resolves to a record: { actor, role } , where role is 'admin' | 'member' . The shared key's two failures both dissolve here — every request now carries an actor , and revoking one person is dropping one record, not a team-wide rotation. Tokens come from layered sources, in precedence order: explicit records → a TEAMKB_TOKENS JSON env → a TEAMKB_TOKENS_FILE (default ~/.teamkb/tokens.json ) → the legacy single TEAMKB_API_KEY , which becomes one admin token with actor "shared" for back-compat. Each entry is a bearer token resolved to an identity at request time. Ma