ci: deploy a preview of each labelled PR

.github/workflows/preview.yml

@@ -0,0 +1,124 @@
+name: Preview
+
+on:
+  pull_request_target:
+    types: [labeled, synchronize, closed]
+
+permissions:
+  contents: read
+  pull-requests: write
+
+concurrency:
+  group: preview-${{ github.event.pull_request.number }}
+  cancel-in-progress: false
+
+env:
+  WRANGLER: wrangler@4.149.0
+  PR_NUMBER: ${{ github.event.pull_request.number }}
+  CLOUDFLARE_ACCOUNT_ID: ${{ vars.PREVIEW_ACCOUNT_ID }}
+  CLOUDFLARE_API_TOKEN: ${{ secrets.PREVIEW_DEPLOY_TOKEN }}
+
+jobs:
+  require-review:
+    name: Require a new review after each push
+    if: github.event.action == 'synchronize' && contains(github.event.pull_request.labels.*.name, 'preview')
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/github-script@v8
+        with:
+          script: |
+            await github.rest.issues.removeLabel({ ...context.repo, issue_number: context.issue.number, name: 'preview' })
+            await github.rest.issues.createComment({
+              ...context.repo,
+              issue_number: context.issue.number,
+              body: 'New commits were pushed. A maintainer must review them and add the `preview` label again to update the preview.'
+            })
+
+  deploy:
+    name: Deploy preview
+    if: github.event.action == 'labeled' && github.event.label.name == 'preview'
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v6
+        with:
+          ref: ${{ github.event.pull_request.head.sha }}
+          persist-credentials: false
+
+      - uses: actions/setup-node@v6
+        with:
+          node-version: "22"
+
+      - name: Install dependencies
+        run: npm ci --ignore-scripts
+
+      - uses: actions/checkout@v6
+        with:
+          path: base
+          persist-credentials: false
+
+      - name: Write preview config
+        id: config
+        run: |
+          mkdir -p .preview
+          node base/scripts/preview-config.mjs "$PR_NUMBER" "${{ vars.PREVIEW_DOMAIN_SUFFIX }}" "${{ vars.PREVIEW_KV_ID }}" "${{ vars.PREVIEW_BUCKET }}" > .preview/out.json
+          echo "url=$(node -p "require('./.preview/out.json').url")" >> "$GITHUB_OUTPUT"
+
+      - name: Deploy
+        run: |
+          npx --yes "$WRANGLER" deploy -c .preview/wrangler.json
+          openssl rand -hex 32 | npx --yes "$WRANGLER" secret put MCP_COOKIE_ENCRYPTION_KEY -c .preview/wrangler.json
+
+      - name: Check the deployed server
+        env:
+          PREVIEW_URL: ${{ steps.config.outputs.url }}
+        run: |
+          for _ in $(seq 1 18); do
+            status=$(curl -s -o /dev/null -w '%{http_code}' -X POST "$PREVIEW_URL" \
+              -H 'content-type: application/json' -H 'accept: application/json, text/event-stream' \
+              -d '{"jsonrpc":"2.0","id":1,"method":"initialize","params":{"protocolVersion":"2025-06-18","capabilities":{},"clientInfo":{"name":"preview-check","version":"1"}}}' || true)
+            [ "$status" = "401" ] && exit 0
+            sleep 10
+          done
+          echo "Expected 401 from $PREVIEW_URL, got $status"
+          exit 1
+
+      - name: Comment the preview URL
+        uses: actions/github-script@v8
+        env:
+          PREVIEW_URL: ${{ steps.config.outputs.url }}
+          HEAD_SHA: ${{ github.event.pull_request.head.sha }}
+        with:
+          script: |
+            const marker = '<!-- mcp-preview -->'
+            const body = [
+              marker,
+              `Preview of ${process.env.HEAD_SHA.slice(0, 7)}: \`${process.env.PREVIEW_URL}\``,
+              '',
+              'Sign in with a Cloudflare API token:',
+              '```',
+              `codex mcp add cf-pr-${context.issue.number} --url ${process.env.PREVIEW_URL} --bearer-token-env-var CF_PREVIEW_TOKEN`,
+              '```',
+              'The preview is deleted when this PR closes.'
+            ].join('\n')
+            const comments = await github.paginate(github.rest.issues.listComments, {
+              ...context.repo,
+              issue_number: context.issue.number
+            })
+            const existing = comments.find((comment) => comment.body?.startsWith(marker))
+            if (existing) {
+              await github.rest.issues.updateComment({ ...context.repo, comment_id: existing.id, body })
+            } else {
+              await github.rest.issues.createComment({ ...context.repo, issue_number: context.issue.number, body })
+            }
+
+  teardown:
+    name: Delete preview
+    if: github.event.action == 'closed' && contains(github.event.pull_request.labels.*.name, 'preview')
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/setup-node@v6
+        with:
+          node-version: "22"
+
+      - name: Delete the preview Worker
+        run: npx --yes "$WRANGLER" delete --name "cloudflare-api-mcp-pr-$PR_NUMBER" --force

.gitignore

@@ -4,3 +4,4 @@ node_modules/
 dist/
 *.log
 .worktrees/
+.preview/

scripts/preview-config.mjs

@@ -0,0 +1,37 @@
+import { writeFileSync } from 'node:fs'
+
+const [prNumber, domainSuffix, kvId, bucketName] = process.argv.slice(2)
+if (!/^\d+$/.test(prNumber ?? '') || !domainSuffix || !kvId || !bucketName) {
+  throw new Error(
+    'Usage: node scripts/preview-config.mjs <pr-number> <domain-suffix> <kv-id> <bucket-name>'
+  )
+}
+
+const name = `cloudflare-api-mcp-pr-${prNumber}`
+const hostname = `pr-${prNumber}.${domainSuffix}`
+
+const config = {
+  name,
+  main: '../src/index.ts',
+  compatibility_date: '2026-06-17',
+  compatibility_flags: ['nodejs_compat', 'global_fetch_strictly_public'],
+  workers_dev: false,
+  preview_urls: false,
+  observability: { logs: { enabled: true } },
+  routes: [{ pattern: hostname, custom_domain: true }],
+  ai: { binding: 'AI' },
+  worker_loaders: [{ binding: 'LOADER' }],
+  services: [{ binding: 'GLOBAL_OUTBOUND', service: name, entrypoint: 'GlobalOutbound' }],
+  kv_namespaces: [{ binding: 'OAUTH_KV', id: kvId }],
+  r2_buckets: [{ binding: 'SPEC_BUCKET', bucket_name: bucketName }],
+  analytics_engine_datasets: [{ binding: 'MCP_METRICS', dataset: 'mcp-metrics-preview' }],
+  vars: {
+    CLOUDFLARE_API_BASE: 'https://api.cloudflare.com/client/v4',
+    CLOUDFLARE_OAUTH_DOMAIN: 'https://dash.cloudflare.com',
+    MCP_RESOURCE: `https://${hostname}/mcp`,
+    OPENAPI_SPEC_URL: 'https://raw.githubusercontent.com/cloudflare/api-schemas/main/openapi.json'
+  }
+}
+
+writeFileSync('.preview/wrangler.json', JSON.stringify(config, null, 2))
+console.log(JSON.stringify({ name, url: config.vars.MCP_RESOURCE }))

src/index.ts

@@ -76,7 +76,7 @@ export default {
     if (isMcpRoute) {
       // Validate Host and browser Origin before authentication so an invalid
       // request cannot spend a bearer token on Cloudflare API identity probes.
-      const rejected = rejectInvalidMcpRequest(request)
+      const rejected = rejectInvalidMcpRequest(request, env.MCP_RESOURCE)
       if (rejected) return rejected
       if (request.method === 'OPTIONS') return handleMcpPreflight(request)
     }

src/mcp-handler.ts

@@ -53,13 +53,23 @@ function createAuthenticatedHandler(props: AuthProps, env?: Env, bearer = '') {
 // - automatic JSON/SSE response shaping (ordinary requests here remain JSON)
 
 /** Validate the deployment boundary before authentication or MCP dispatch. */
-export function rejectInvalidMcpRequest(request: Request): Response | undefined {
+export function rejectInvalidMcpRequest(
+  request: Request,
+  mcpResource?: string
+): Response | undefined {
+  const deployedHostname = deployedHostnameOf(mcpResource)
   return (
-    hostHeaderValidationResponse(request, ALLOWED_MCP_HOSTNAMES) ??
-    originValidationResponse(request, ALLOWED_MCP_ORIGIN_HOSTNAMES)
+    hostHeaderValidationResponse(request, [...ALLOWED_MCP_HOSTNAMES, ...deployedHostname]) ??
+    originValidationResponse(request, [...ALLOWED_MCP_ORIGIN_HOSTNAMES, ...deployedHostname])
   )
 }
 
+function deployedHostnameOf(mcpResource: string | undefined): string[] {
+  if (!mcpResource || !URL.canParse(mcpResource)) return []
+  const url = new URL(mcpResource)
+  return url.protocol === 'https:' ? [url.hostname] : []
+}
+
 function corsHeaders(request: Request): Headers | undefined {
   const origin = request.headers.get('Origin')
   if (!origin) return undefined
@@ -105,7 +115,7 @@ export async function handleAuthenticatedMcpRequest(
     return new Response('Not Found', { status: 404 })
   }
 
-  const rejected = rejectInvalidMcpRequest(request)
+  const rejected = rejectInvalidMcpRequest(request, env?.MCP_RESOURCE)
   if (rejected) return rejected
 
   const props = AuthPropsSchema.parse(rawProps)

tests/mcp-deployed-host.test.ts

@@ -0,0 +1,37 @@
+import { describe, expect, it } from 'vitest'
+import { rejectInvalidMcpRequest } from '../src/mcp-handler'
+
+function requestFor(host: string, origin?: string): Request {
+  return new Request(`https://${host}/mcp`, {
+    method: 'POST',
+    headers: { Host: host, ...(origin ? { Origin: origin } : {}) }
+  })
+}
+
+describe('deployed MCP hostname', () => {
+  it('accepts the hostname of the deployment MCP_RESOURCE names', () => {
+    const host = 'pr-42.mcp-preview.example.dev'
+    expect(
+      rejectInvalidMcpRequest(requestFor(host, `https://${host}`), `https://${host}/mcp`)
+    ).toBeUndefined()
+  })
+
+  it('rejects that hostname when MCP_RESOURCE names a different deployment', () => {
+    const response = rejectInvalidMcpRequest(
+      requestFor('pr-42.mcp-preview.example.dev'),
+      'https://mcp.cloudflare.com/mcp'
+    )
+    expect(response?.status).toBe(403)
+  })
+
+  it('does not trust a plain-HTTP or malformed MCP_RESOURCE', () => {
+    expect(
+      rejectInvalidMcpRequest(requestFor('evil.example'), 'http://evil.example/mcp')?.status
+    ).toBe(403)
+    expect(rejectInvalidMcpRequest(requestFor('evil.example'), 'not a url')?.status).toBe(403)
+  })
+
+  it('keeps accepting the production hostname without MCP_RESOURCE', () => {
+    expect(rejectInvalidMcpRequest(requestFor('mcp.cloudflare.com'))).toBeUndefined()
+  })
+})