Namespace Nexus\Mcp\Server\Transport\Http\Middleware

Makes the MCP endpoint an OAuth 2.1 resource server: it requires a bearer token, binds that token's audience to this server, and enforces the scopes the endpoint calls for. A request presenting no bearer credential is answered 401 with a WWW-Authenticate challenge naming the Protected Resource Metadata document, one presenting a bearer credential that cannot be read is answered 400 invalid_request, and a token that is valid but too narrow is answered 403 insufficient_scope. The validated token reaches request handlers on ServerContext::$receiveContext->authInfo.

Grants browser clients cross-origin access to the MCP endpoint. The middleware is additive. An allowed Origin is reflected into Access-Control-Allow-Origin, a preflight OPTIONS is answered with 204 plus the negotiated Access-Control-* headers, and every other request is forwarded and its response decorated. A disallowed or absent Origin receives no grant, so rejection stays with the DNS-rebinding gate. Every response carries the Vary keys it turns on, grant or not, so a shared cache cannot serve one origin's answer to another.

Guards the MCP endpoint against DNS rebinding by rejecting requests from an unrecognised Origin or Host. A present-but-unlisted Origin is answered with an id-less JSON-RPC error on HTTP 403. A request without an Origin header (non-browser clients) passes through, since only browsers send it. Host validation is a beyond-spec, opt-in dimension: an empty allow-list disables it, otherwise the Host header must be present and listed. Matching is case-insensitive, since RFC 9110 makes the scheme and host of a URI so.

Rejects a tools/call whose Mcp-Param-{Name} headers disagree with the arguments in its body. The spec requires any server that processes the body to validate the mirrored headers against it, so an intermediary routing on a header value cannot disagree with what the server executes. Bindings are read from the tool inputSchema declarations once and cached, and the cache is dropped whenever a ListChangeSourceInterface store reports that its listing changed.

Rejects a request whose body exceeds a configured byte cap before it reaches the transport. An oversized body is answered with an id-less JSON-RPC error on HTTP 413, sparing the transport the cost of stringifying and parsing it. The cap is measured against the buffered body size. A body whose size cannot be determined passes through, leaving a streaming cap to the HTTP server.