diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index bcacce0..49b551a 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -48,6 +48,9 @@ jobs:
       - name: Typecheck governed authority service
         run: ./reference-implementations/trust-authority/node_modules/.bin/tsc -p services/authority/tsconfig.json
 
+      - name: Test governed authority using synthetic loopback HTTP scenarios
+        run: node scripts/check-authority-staging.mjs
+
       - name: Go verifier regression and concurrency tests
         run: |
           go version
diff --git a/scripts/check-authority-staging.mjs b/scripts/check-authority-staging.mjs
new file mode 100644
index 0000000..ce4d1f5
--- /dev/null
+++ b/scripts/check-authority-staging.mjs
@@ -0,0 +1,132 @@
+#!/usr/bin/env node
+// Synthetic local staging harness: no cloud calls, no real GitHub approvals.
+import assert from 'node:assert/strict';
+import crypto from 'node:crypto';
+import {spawn,spawnSync} from 'node:child_process';
+import net from 'node:net';
+import os from 'node:os';
+import fs from 'node:fs';
+import path from 'node:path';
+import {fileURLToPath} from 'node:url';
+
+const root=path.resolve(path.dirname(fileURLToPath(import.meta.url)),'..');
+const tmp=fs.mkdtempSync(path.join(os.tmpdir(),'ttp-cfav-authority-'));
+const token='synthetic-token-'+crypto.randomBytes(32).toString('hex');
+const key='synthetic-hmac-'+crypto.randomBytes(32).toString('hex');
+const now=new Date();
+const verifiedAt=new Date(now.getTime()-15000).toISOString();
+const validUntil=new Date(now.getTime()+1800000).toISOString();
+const expired=new Date(now.getTime()-60000).toISOString();
+const grant=(updates={})=>({
+  subject:'wi://github/actions/runner',repo:'BlockSiFr/ttp-protocol',
+  action:'pull_request.execute',branch:'cfav-synthetic-branch',
+  trustScore:0.95,verifiedAt,expiresAt:validUntil,...updates
+});
+const grants={
+  'grant-valid':grant(),
+  'grant-revoked':grant({revoked:true}),
+  'grant-expired':grant({expiresAt:expired}),
+  'grant-stale':grant({verifiedAt:new Date(now.getTime()-1000000).toISOString()}),
+  'grant-other-tenant':grant({repo:'other/tenant'})
+};
+const config=path.join(root,'services/authority/tsconfig.json');
+const tsc=path.join(root,'reference-implementations/trust-authority/node_modules/.bin/tsc');
+const compiled=path.join(tmp,'compiled');
+const build=spawnSync(tsc,['-p',config,'--noEmit','false','--outDir',compiled],
+  {cwd:root,encoding:'utf8',timeout:120000});
+if(build.status!==0)throw Error('cannot compile authority: '+build.stderr+build.stdout);
+const binary=path.join(compiled,'index.js');
+assert.ok(fs.existsSync(binary),'compiled authority entry missing');
+
+const probe=net.createServer();
+const port=await new Promise((resolve,reject)=>{
+  probe.once('error',reject);
+  probe.listen(0,'127.0.0.1',()=>resolve(probe.address().port));
+});
+await new Promise(resolve=>probe.close(resolve));
+let server;
+try{
+  server=spawn(process.execPath,[binary],{
+    cwd:root,stdio:['ignore','pipe','pipe'],
+    env:{...process.env,PORT:String(port),RUNTIME_AUTH_TOKEN:token,
+      RECEIPT_HMAC_SECRET:key,RUNTIME_AUTH_GRANTS_JSON:JSON.stringify(grants)}
+  });
+  let stderr='';
+  server.stderr.on('data',chunk=>{stderr+=chunk.toString().slice(0,2000)});
+  const url='http://127.0.0.1:'+port;
+  let healthy=false;
+  for(let i=0;i<70;i++){
+    if(server.exitCode!==null)throw Error('authority exited: '+stderr);
+    try {
+      const result=await fetch(url+'/healthz',{signal:AbortSignal.timeout(600)});
+      if(result.status===200){healthy=true;break}
+    }catch{}
+    await new Promise(resolve=>setTimeout(resolve,100));
+  }
+  assert.ok(healthy,'synthetic authority did not listen');
+
+  const base={
+    subject:'wi://github/actions/runner',action:'pull_request.execute',
+    resource:'repo:BlockSiFr/ttp-protocol:pr/100',repo:'BlockSiFr/ttp-protocol',
+    branch:'cfav-synthetic-branch',pathsTouched:['docs/README.md'],
+    commitSha:'a'.repeat(40),invokingActor:'synthetic-contributor',
+    workflowRunId:'111222333',attestationRef:'synthetic-only',
+    authorityGrantRef:'grant-valid',context:{event:'pull_request'}
+  };
+  async function request(body,suppliedToken=token){
+    const r=await fetch(url+'/re/authorize',{
+      method:'POST',
+      headers:{'content-type':'application/json',
+        ...(suppliedToken?{authorization:'Bearer '+suppliedToken}:{})},
+      body:JSON.stringify(body)
+    });
+    return {status:r.status,json:await r.json()};
+  }
+  for(const auth of ['','forged-caller']){
+    const r=await request(base,auth);
+    assert.equal(r.status,401,'invalid bearer');
+  }
+  for(const ref of ['absent','grant-revoked','grant-expired','grant-other-tenant']){
+    const r=await request({...base,authorityGrantRef:ref,trustScore:1,freshnessSeconds:0});
+    assert.equal(r.json.decision,'DENY','missing, revoked, expired or mismatched grant');
+  }
+  const stale=await request({...base,authorityGrantRef:'grant-stale',trustScore:1,freshnessSeconds:0});
+  assert.notEqual(stale.json.decision,'PERMIT','stale grant cannot permit');
+  const allowed=await request({...base,trustScore:0,freshnessSeconds:999999});
+  assert.equal(allowed.status,200);
+  assert.equal(allowed.json.decision,'PERMIT','must rely on operator grant');
+  assert.equal(allowed.json.receipt.commitSha,base.commitSha);
+  assert.equal(allowed.json.receipt.pathsTouched[0],base.pathsTouched[0]);
+  assert.equal(allowed.json.receipt.workflowRunId,base.workflowRunId);
+  const {signature,...unsigned}=allowed.json.receipt;
+  const digest='hmac-sha256:'+crypto.createHmac('sha256',key).update(JSON.stringify(unsigned)).digest('hex');
+  assert.equal(signature,digest,'receipt HMAC verified using provisioned fixture key');
+
+  const protectedReq={...base,pathsTouched:['.github/workflows/ci.yml']};
+  const stepup=await request(protectedReq);
+  assert.equal(stepup.json.decision,'STEP_UP');
+  const reauth={...protectedReq,action:'merge request reauthorize',
+    priorReceiptId:stepup.json.receiptId,
+    approval:{environment:'protected-execution',approved:true,approvedBy:'independent-synthetic-reviewer'}};
+  assert.equal((await request({...reauth,priorReceiptId:allowed.json.receiptId})).json.decision,'DENY');
+  assert.equal((await request({...reauth,commitSha:'b'.repeat(40)})).json.decision,'DENY');
+  assert.equal((await request({...reauth,pathsTouched:['.github/workflows/other.yml']})).json.decision,'DENY');
+  assert.equal((await request({...reauth,approval:undefined})).json.decision,'DENY');
+  const approved=await request(reauth);
+  assert.equal(approved.json.decision,'PERMIT','synthetic post-step-up permit');
+  assert.notEqual(approved.json.receiptId,stepup.json.receiptId);
+  assert.equal(approved.json.receipt.priorReceiptId,stepup.json.receiptId);
+  const bad=await fetch(url+'/re/authorize',{
+    method:'POST',headers:{authorization:'Bearer '+token,'content-type':'application/json'},body:'{broken-json'});
+  assert.equal(bad.status,400);
+  console.log('CFAV synthetic authority HTTP PASS: authentication, scoped grants, freshness, bound receipts, STEP_UP, reauthorization and negative controls.');
+  console.log('Not a live GitHub reviewer approval or production deployment.');
+}finally{
+  if(server){
+    server.kill('SIGTERM');
+    await Promise.race([new Promise(resolve=>server.once('exit',resolve)),
+      new Promise(resolve=>setTimeout(resolve,1500))]);
+    if(server.exitCode===null)server.kill('SIGKILL');
+  }
+  fs.rmSync(tmp,{force:true,recursive:true});
+}
diff --git a/services/authority/README.md b/services/authority/README.md
index 3227f4e..627dddd 100644
--- a/services/authority/README.md
+++ b/services/authority/README.md
@@ -9,7 +9,7 @@ Set these values in a trusted server-side secret store, not in the GitHub reposi
 - `RUNTIME_AUTH_TOKEN`: unique bearer credential of at least 32 bytes, shared only with the trusted GitHub workflow; never expose to PR code.
 - `RECEIPT_HMAC_SECRET`: independently provisioned signing key of at least 32 bytes. The former development signing fallback has been removed.
 - `RUNTIME_AUTH_GRANTS_JSON`: operator-provisioned mapping from opaque grant IDs to `{subject, repo, action, branch?, expiresAt, trustScore, verifiedAt, revoked?}`. Grant state must be obtained from independently authenticated issuer/operator evidence, not request text. `verifiedAt` must be fresh within 900 seconds.
-- `PORT`: trusted listener port (default `8080`). Terminate TLS and authenticate workload identity with an approved fronting gateway.
+- `PORT`: trusted listener port (default `8080`). The service listens only on `127.0.0.1`, not on a public interface. Terminate TLS and authenticate workload identity with an approved same-host fronting gateway.
 
 An example **synthetic** grant structure, without credentials:
 
@@ -38,3 +38,7 @@ The workflow additionally requires GitHub Actions secrets `RUNTIME_AUTH_URL`, `R
 Caller-supplied `trustScore`, `freshnessSeconds` or claimed grant IDs never establish trust by themselves. Unknown or stale grants deny or escalate; they do not permit. Step-up reauthorization requires prior receipt continuity, freshness and independently authenticated GitHub approval evidence.
 
 **Remaining P0 integration:** independently verified GitHub/OIDC workload identity, live negative/positive HTTPS tests, durable signed receipt storage, production-grade issuer and revocation registry, KMS/HSM key custody, tenant separation and target-side completion verification. HMAC receipts are not publicly verifiable Ed25519 receipts. Keep this service inaccessible from untrusted networks until those gates are met.
+
+## Local synthetic HTTP acceptance evidence
+
+`node scripts/check-authority-staging.mjs` compiles and starts this service locally with **throwaway, synthetic credentials and grants** and executes a full positive/negative HTTP matrix. GitHub CI runs this by default. This tests service behavior but does **not** authenticate the GitHub Approvals API, validate actual OIDC identity or satisfy any production deployment requirement.
diff --git a/services/authority/index.ts b/services/authority/index.ts
index b1bdf33..25acb62 100644
--- a/services/authority/index.ts
+++ b/services/authority/index.ts
@@ -268,7 +268,11 @@ const server = http.createServer(async (req, res) => {
 })
 
 const port = Number(process.env.PORT ?? "8080")
-server.listen(port, () => {
-  // eslint-disable-next-line no-console
-  console.log(`[authority] listening on :${port}`)
+if (!Number.isInteger(port) || port < 1 || port > 65535) {
+  throw new Error("PORT must be an integer in the range 1 to 65535")
+}
+// Safe default: bearer credentials must not traverse an exposed plaintext HTTP
+// socket. Terminate TLS at an approved local fronting proxy/sidecar.
+server.listen(port, "127.0.0.1", () => {
+  console.log(`[authority] local listener on 127.0.0.1:${port}; use approved TLS fronting gateway`)
 })
diff --git a/tests/governed-workflow-security.test.mjs b/tests/governed-workflow-security.test.mjs
index c3a4f26..ed38f98 100644
--- a/tests/governed-workflow-security.test.mjs
+++ b/tests/governed-workflow-security.test.mjs
@@ -63,3 +63,9 @@ test('CFAV: authority starter cannot accept unauthenticated users or default sig
   assert.doesNotMatch(signer,/dev-only-secret/);
   assert.match(signer,/RECEIPT_HMAC_SECRET/);
 });
+
+test('CFAV: starter authority never exposes bearer authentication on an unrestricted HTTP listener',()=>{
+  const authority=fs.readFileSync('services/authority/index.ts','utf8');
+  assert.match(authority,/server\.listen\(port, "127\.0\.0\.1"/);
+  assert.match(authority,/PORT must be an integer/);
+});