Fixing the CSRF Token Missing Error in Flask with Vue.js

Learn how to properly fetch and set the CSRF token in your Vue.js application using Flask to avoid the `CSRF Token Missing` error during POST requests.
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This video is based on the question https://stackoverflow.com/q/67417495/ asked by the user 'ajrlewis' ( https://stackoverflow.com/u/5058116/ ) and on the answer https://stackoverflow.com/a/67477360/ provided by the user 'Vigen' ( https://stackoverflow.com/u/3649767/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Solving the CSRF Token Missing Error in Your Flask and Vue.js Application

Creating applications that involve both Flask as a backend and Vue.js as a frontend can be tricky when it comes to handling Cross-Site Request Forgery (CSRF) tokens. A common problem you might encounter is the error that states "The CSRF token is missing" when you attempt to send a POST request. In this post, we'll break down how you can properly fetch and set the CSRF token to avoid this issue.

Understanding the Problem

CSRF tokens are crucial for securing your application against unauthorized requests. Without them, any attempt to make a POST request can lead to a security vulnerability. However, integrating CSRF protection into your application can sometimes lead to errors, particularly if the token isn't being fetched or set correctly. The error message you're receiving indicates that the CSRF token is not present in your request headers when making a POST request.

Your Application Structure

Your backend is built using Flask and includes the flask_wtf package for CSRF protection. The basic structure of your application includes two files: __init__.py and sanity_bp.py where you’ve set up your routes and CSRF token generation. Here's a brief breakdown of how it's currently configured:

Backend Setup (__init__.py and sanity_bp.py)

CORS and CSRF Initialization: You are properly initializing both CORS and CSRF in your Flask app.

CSRF Token Generation: The get_csrf() method generates and returns a CSRF token when you hit the /get/csrf endpoint.

POST Request Handling: The /post route is designed to handle POST requests but requires the CSRF token.

Frontend Setup

On the Vue.js side, you are using Axios to make API requests to your Flask server. The following points summarize your setup:

Fetching CSRF Token: You defined a csrf() method that fetches the token and assigns it to a header for subsequent POST requests.

Data Submission: The sanity() method sends a POST request that is supposed to include the CSRF token.

The Solution

Your bug arises from the fact that the csrf() function is asynchronous. This means that when you call the sanity() function in your created() lifecycle hook, the CSRF token may not have been fetched and set as the request header in time.

How to Fix It

To ensure that the CSRF token is fetched and set before trying to send any POST requests, you should utilize the async/await syntax. Here’s how you can modify your code:

[[See Video to Reveal this Text or Code Snippet]]

Key Changes Made

Used async/await: This allows your created() function to wait for the CSRF token to be fetched before making the POST request.

Updated sanity() Method: Changed to an async function to handle the asynchronous POST request properly.

Conclusion

By implementing these changes, you can ensure that your Vue.js frontend correctly fetches and sets the CSRF token before making any POST requests to your Flask backend. This should eliminate the "CSRF token is missing" error, allowing your application to function securely and seamlessly.

Now, you can continue building your application with the confidence that your CSRF protection is implemented correctly. Happy coding!

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