fix(private-server): accept the deployment Host on the MCP endpoint#273
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rmcp's Streamable HTTP DNS-rebinding guard defaults allowed_hosts to loopback only, so the production tailnet host got 'Forbidden: Host header is not allowed' (which clients surface as 'needs authentication'). The endpoint is already gated by the Tailscale ingress, the tagged-device guard, and the tailnet-user check, and serves no CORS headers, so the browser-oriented host check is redundant here. Disable it by default; an operator can still pin hosts via CANOPY_MCP_ALLOWED_HOSTS. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
This was referenced Jun 25, 2026
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🤖 The MCP endpoint (
/api/mcp) returnsForbidden: Host header is not allowedfor any non-loopback host, so connecting from the production tailnet URL fails — clients (Claude Code) surface this as "needs authentication".Cause
rmcp's Streamable HTTP transport ships a DNS-rebinding guard whose
allowed_hostsdefaults to loopback only (localhost,127.0.0.1,::1). That defense is aimed at browser-facing localhost MCP servers; it doesn't fit this deployment, where the endpoint is reachable only through the Tailscale ingress (which injects the caller's identity), behind the tagged-device guard and the tailnet-user gate, and serves no CORS headers (so a browser can't make a cross-origin POST to it).Fix
Disable the Host allowlist by default. An operator who still wants to pin it can set
CANOPY_MCP_ALLOWED_HOSTSto a comma-separated list (e.g.canopy.example.ts.net); loopback stays allowed for local dev.Adds a regression test asserting a non-loopback
Hostis accepted.