Solving Invalid CSRF TOKEN Error in Node.js with Multer

Learn how to resolve the `invalid CSRF token` issue in your Node.js application using Multer for file uploads. This guide provides a step-by-step solution with code examples. --- This video is based on the question https://stackoverflow.com/q/67072706/ asked by the user 'Hussain Shaikh' ( https://stackoverflow.com/u/5234084/ ) and on the answer https://stackoverflow.com/a/67073345/ provided by the user 'O. Jones' ( https://stackoverflow.com/u/205608/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions. Visit these links for original content and any more details, such as alternate solutions, latest updates/developments on topic, comments, revision history etc. For example, the original title of the Question was: Invalid CSRF TOKEN Node js multer Also, Content (except music) licensed under CC BY-SA https://meta.stackexchange.com/help/licensing The original Question post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/by-sa/4.0/ ) license, and the original Answer post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/by-sa/4.0/ ) license. If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com. --- Understanding the Invalid CSRF TOKEN Error in Node.js with Multer When developing web applications, ensuring the security of your forms and file uploads is paramount. One common issue developers face is the Invalid CSRF TOKEN error. This error typically arises when making asynchronous requests to your server, and it signifies that the server has rejected the incoming request due to a mismatch in authorization tokens. In this guide, we’ll explore why this happens in a Node.js environment with Multer and how to effectively resolve it. The Problem In your scenario, you are using fetch() to asynchronously upload files via an HTML form. While the form can successfully submit data using a normal POST request, it failed during the asynchronous attempt. The server responded with an error message indicating the invalid CSRF token. Let's break this down: CSRF Tokens: Cross-Site Request Forgery (CSRF) tokens are security credentials that help prevent unauthorized commands. Your server expects a valid token for any POST requests, especially for actions like file uploads. Form Configuration: You have set up a form with CSRF protection, but the fetch() request to your server didn’t include the necessary CSRF token, causing the server to reject the request. The Solution To successfully carry out an asynchronous file upload while adhering to CSRF protections, follow these outlined steps: Step 1: Modify the HTML Form Make sure your HTML form properly includes the CSRF token. Every input in your form that needs to be submitted should have a name attribute. This allows the server to recognize them when they are sent via the request. Here’s how your modified form should look: [[See Video to Reveal this Text or Code Snippet]] Step 2: Update the JavaScript Fetch Request Next, retrieve the CSRF token from your form and append it to the FormData object before sending the request. Here’s an updated version of your JavaScript code: [[See Video to Reveal this Text or Code Snippet]] Step 3: Server-Side Configuration Ensure that your server is set up to validate CSRF tokens properly. Here’s an overview of the critical sections: CSRF Middleware Setup: Make sure you have the csurf middleware in use. Session Management: CSRF tokens depend on session management, which should be properly configured in your Node.js setup. Token Retrieval: Use res.locals.csrfToken to generate a unique token for each session and form render. [[See Video to Reveal this Text or Code Snippet]] Step 4: Continuous Token Validation When you submit the form, the server checks if the _csrf token sent with the request matches the one stored in the user’s session. If they match, the action can proceed; if not, the server will reject the request, thus preventing potential CSRF attacks. Conclusion Incorporating CSRF tokens in your file upload process is crucial for securing your web applications. By following the steps outlined above, you can effectively resolve the Invalid CSRF TOKEN error while ensuring that your data remains safe and secure. Always remember to maintain proper session management and verify tokens on both the client and server sides. Happy coding!