feat(mcp): mcpAuth middleware — agent bearer + space scope + rate limit

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

lib/api/middleware/mcp_auth.js

@@ -0,0 +1,44 @@
+// Auth gate for /mcp. External agents must present a Void agent bearer token
+// bound to a Space (scopes.space_id). Owner / CF-Access identities are NOT
+// accepted here — external agents never inherit owner powers. CF Access service
+// tokens are enforced at the edge (Cloudflare policy on mcp.void.hynesy.com).
+import * as agents from '../../db/repos/agents.js';
+
+// Minimal fixed-window in-memory rate limit per token (defense-in-depth; the
+// real gate is CF Access + bearer). Window is 60s.
+const WINDOW_MS = 60_000;
+const hits = new Map(); // token -> { count, resetAt }
+export function _resetMcpRate() { hits.clear(); }
+function rateLimited(token) {
+  const limit = Number(process.env.MCP_RATE_LIMIT || 120);
+  const now = Date.now();
+  let h = hits.get(token);
+  if (!h || now > h.resetAt) { h = { count: 0, resetAt: now + WINDOW_MS }; hits.set(token, h); }
+  h.count += 1;
+  return h.count > limit;
+}
+
+export async function mcpAuth(req, res, next) {
+  const auth = req.headers.authorization || '';
+  const [scheme, token] = auth.split(' ');
+  if (scheme !== 'Bearer' || !token) {
+    return res.status(401).json({ error: { code: 'unauthorized', message: 'missing bearer token' } });
+  }
+  if (process.env.OWNER_TOKEN && token === process.env.OWNER_TOKEN) {
+    return res.status(401).json({ error: { code: 'agent_required', message: 'owner token not valid for MCP' } });
+  }
+  if (rateLimited(token)) {
+    return res.status(429).json({ error: { code: 'rate_limited', message: 'too many requests' } });
+  }
+  let agent;
+  try { agent = await agents.verifyToken(token); }
+  catch (e) { return next(e); }
+  if (!agent) {
+    return res.status(401).json({ error: { code: 'unauthorized', message: 'invalid token' } });
+  }
+  if (!(agent.scopes && agent.scopes.space_id)) {
+    return res.status(403).json({ error: { code: 'no_space_scope', message: 'agent has no space scope' } });
+  }
+  req.mcpAgent = agent;
+  next();
+}