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harden: add CSRF protection in server.js... #4413

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harden: add CSRF protection in server.js... #4413

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7ea55f4
fix: javascript.express.security.audit.express-check-csurf-middleware…
anupamme Aug 20, 2026
16ffe80
Address review feedback (2 comments)
anupamme Aug 21, 2026
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2 changes: 2 additions & 0 deletions appengine/building-an-app/update/package.json
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Original file line number Diff line number Diff line change
Expand Up @@ -19,6 +19,8 @@
"author": "Google Inc.",
"license": "Apache-2.0",
"dependencies": {
"cookie-parser": "^1.4.6",
"csurf": "^1.11.0",
"express": "^4.18.2"
},
"devDependencies": {
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19 changes: 17 additions & 2 deletions appengine/building-an-app/update/server.js
100755 → 100644
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Expand Up @@ -16,22 +16,37 @@

// [START gae_update_web_server_app]
const express = require('express');
const cookieParser = require('cookie-parser');
const csrf = require('csurf');
Comment on lines +19 to +20

@gemini-code-assist gemini-code-assist Bot Aug 20, 2026

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medium

To avoid hardcoding the HTML form in server.js and keep using the existing views/form.html template, we need to import the fs and path modules. This allows us to read the HTML file asynchronously and inject the CSRF token dynamically.

Suggested change
const cookieParser = require('cookie-parser');
const csrf = require('csurf');
const cookieParser = require('cookie-parser');
const csrf = require('csurf');
const fs = require('fs').promises;
const path = require('path');
References
  1. For asynchronous file system operations in Node.js, use the promise-based fs.promises API when working with async/await.

const fs = require('fs').promises;
const path = require('path');

const app = express();

// [START gae_enable_parser]
// This middleware is available in Express v4.16.0 onwards
app.use(cookieParser());
app.use(express.urlencoded({extended: true}));
app.use(csrf({cookie: true}));
// [END gae_enable_parser]

app.get('/', (req, res) => {
res.send('Hello from App Engine!');
});

// [START gae_add_display_form]
app.get('/submit', (req, res) => {
res.sendFile(path.join(__dirname, '/views/form.html'));
app.get('/submit', async (req, res, next) => {
try {
const token = req.csrfToken();
const template = await fs.readFile(path.join(__dirname, '/views/form.html'), 'utf-8');
const html = template.replace(
'<form method="POST" action="/submit">',
`<form method="POST" action="/submit"><input type="hidden" name="_csrf" value="${token}">`
);
res.send(html);
} catch (err) {
next(err);
}
});
// [END gae_add_display_form]

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