MCP Gateway: Authority-injection and JWT/session bypass via the unauthenticated router hair-pin "router-key" / "mcp-init-host" path
The MCP router (ext_proc) exposes an initialize-method code path that, when a request carries an mcp-init-host header, bypasses the gateway JWT session validator and rewrites the upstream :authority header to whatever the caller chooses, gated only by a single shared header value (router-key). The shared value is a literal string (secret-api-key) baked into cmd/mcp-broker-router/main.go as a fall-back default, and in controller-managed deployments, a SHA-256 truncation of the MCPGatewayExtension UID — …